How does evolutionary theory explain the consistent 10% of left-handed individuals in the population. What factors contribute to the prevalence of left-handedness. How do competition and cooperation influence handedness distribution in human societies.

The Prevalence of Left-Handedness: A 10% Constant

Left-handedness has long been a subject of fascination and curiosity. Despite the challenges faced by left-handed individuals in a predominantly right-handed world, the percentage of lefties has remained remarkably stable throughout human history. Approximately 10% of the global population is left-handed, a figure that has persisted for an estimated 500,000 years.

This consistent prevalence raises intriguing questions about the factors that influence handedness and why left-handedness has neither increased nor decreased significantly over time. To understand this phenomenon, we must delve into the realms of evolutionary theory, genetics, and social dynamics.

The Evolutionary Perspective: Competition vs. Cooperation

Evolutionary theory offers a compelling explanation for the persistence of left-handedness in human populations. The key lies in the delicate balance between two fundamental forces: competition and cooperation.

The Competitive Edge of Left-Handedness

In competitive scenarios, particularly in hand-to-hand combat or sports, left-handedness can provide a distinct advantage. This is due to the element of surprise and the fact that most individuals are accustomed to facing right-handed opponents. This phenomenon is known as negative frequency-dependent selection, where a trait becomes more advantageous as it becomes rarer in a population.

How does this competitive advantage manifest in real-world scenarios? In combat sports such as boxing or fencing, left-handed fighters often have an initial upper hand as their opponents must adjust their strategies and techniques. Similarly, in team sports like baseball or cricket, left-handed batters or pitchers can create unexpected challenges for their adversaries.

The Cooperative Constraints on Left-Handedness

While competition might favor an increase in left-handedness, cooperation acts as a counterbalance. In cooperative settings, which are crucial for societal development and progress, left-handed individuals often face disadvantages. This is primarily because most tools, machinery, and social customs are designed with the right-handed majority in mind.

Consider the challenges left-handed people encounter in everyday life: using scissors, writing in notebooks with spiral bindings, or operating various tools and equipment. These difficulties arise from the fact that our cooperative society has largely been built around right-handed norms.

The Genetic Puzzle of Handedness

While the evolutionary perspective offers insights into the maintenance of left-handedness in populations, the underlying genetic factors remain somewhat elusive. Researchers have long sought to uncover the genetic basis of handedness, but the picture is far from complete.

Is Left-Handedness Inherited?

There is evidence to suggest that handedness has a genetic component, but it’s not a simple case of inheritance. Left-handed parents are more likely to have left-handed children, but the relationship is not straightforward. Even in pairs of identical twins, who share the same genetic makeup, it’s possible for one twin to be left-handed and the other right-handed.

What genetic factors might influence handedness? While no single “left-handed gene” has been identified, researchers have found several genes that may play a role in determining handedness. These genes are often involved in brain development and asymmetry, suggesting that handedness is linked to broader patterns of brain organization.

Biological and Environmental Influences on Handedness

Beyond genetics, various biological and environmental factors have been proposed to influence handedness. These theories attempt to explain not only why some individuals are left-handed but also why the proportion of left-handers remains relatively constant.

The Role of Sex Hormones

One intriguing hypothesis suggests that prenatal exposure to sex hormones, particularly testosterone, may influence handedness. This theory is supported by the observation that slightly more males than females are left-handed. How might testosterone affect handedness? It’s thought that higher levels of testosterone in the womb may influence brain development, potentially increasing the likelihood of left-handedness.

Fetal Positioning and Handedness

Another theory proposes that the position of the fetus in the womb during late pregnancy might influence handedness. According to this idea, fetuses that favor a rightward position are more likely to develop left-handedness. While this hypothesis is intriguing, more research is needed to establish a clear link between fetal positioning and eventual handedness.

The Cultural and Historical Context of Left-Handedness

Throughout history, left-handedness has been viewed differently across cultures. In many societies, it has been associated with negative connotations, leading to attempts to “correct” left-handedness in children. This cultural bias may have influenced the expression of handedness and contributed to maintaining the proportion of left-handers at around 10%.

Historical Stigma and Its Effects

How has the historical stigma against left-handedness affected its prevalence? In many Western cultures, left-handed children were often forced to use their right hands for writing and other tasks. This practice, known as “switching,” may have artificially suppressed the number of left-handed individuals in previous generations. As societal attitudes have become more accepting, some researchers have observed a slight increase in reported left-handedness, although the overall proportion remains close to 10%.

The Neurological Basis of Handedness

Understanding the neurological underpinnings of handedness provides further insights into its origins and persistence in human populations. While early theories suggested a simple relationship between brain lateralization and handedness, the reality is more complex.

Brain Asymmetry and Handedness

How does brain organization relate to handedness? Contrary to popular belief, handedness is not simply determined by which hemisphere of the brain is dominant. Both left- and right-handed individuals show similar patterns of brain lateralization for functions such as language. However, there are subtle differences in brain organization between left- and right-handers, particularly in motor areas.

Recent neuroimaging studies have revealed that left-handed individuals often show more symmetrical brain organization compared to right-handers. This increased symmetry may contribute to some of the cognitive and creative advantages sometimes associated with left-handedness.

The Advantages and Challenges of Left-Handedness

While left-handedness can present challenges in a right-hand dominant world, it also comes with potential advantages. Understanding these can help explain why left-handedness persists in the population despite certain disadvantages.

Cognitive and Creative Benefits

Are left-handed individuals more creative or intellectually gifted? While popular culture often associates left-handedness with increased creativity and intelligence, the scientific evidence is mixed. Some studies have found a higher proportion of left-handers in creative professions and among high achievers in certain fields. However, these findings are not consistent across all studies, and the relationship between handedness and cognitive abilities remains a topic of ongoing research.

Adapting to a Right-Handed World

How do left-handed individuals navigate a world designed for right-handers? From scissors to can openers, many everyday tools pose challenges for lefties. This constant need to adapt may foster increased problem-solving skills and cognitive flexibility. Some researchers suggest that these adaptive strategies could contribute to the cognitive advantages sometimes observed in left-handed individuals.

Future Perspectives on Handedness Research

As our understanding of genetics, neuroscience, and human evolution continues to advance, new insights into the origins and implications of handedness are likely to emerge. Future research may shed light on the complex interplay between genetic, environmental, and cultural factors that influence handedness.

Emerging Technologies and Handedness Research

How might new technologies contribute to our understanding of handedness? Advanced neuroimaging techniques, combined with large-scale genetic studies, may reveal more about the biological basis of handedness. Additionally, research into epigenetics – the study of how environmental factors can influence gene expression – may provide new perspectives on how handedness develops and is maintained in populations.

As we continue to explore the fascinating world of handedness, it’s clear that the persistence of left-handedness at around 10% of the population is the result of a complex interplay of evolutionary, genetic, and cultural factors. This delicate balance between competition and cooperation, combined with the unique challenges and potential advantages of being left-handed, ensures that lefties will likely remain a significant minority in human populations for generations to come.

Understanding the factors that contribute to handedness not only satisfies our curiosity about human diversity but also has practical implications. From designing more inclusive tools and environments to potentially unlocking new insights into brain organization and cognitive development, the study of handedness continues to offer valuable contributions to our understanding of human biology and behavior.

Why is left-handedness rare? It comes down to these 2 words

I’m left-handed, which means I’ve spent my entire life fumbling with scissors, wiping ink smudges from my pinky finger, and thumbing through magazines backwards. I’ve always accepted that being left-handed comes with certain challenges, but one thing about the condition has long perplexed me: Why are we lefties so damn rare?

It turns out, a plausible answer may be found in evolutionary theory. After googling a number of left-handed factoids in anticipation of International Left-Handers Day, which is today, I stumbled across a fascinating TED-Ed lesson from Daniel M. Abrams, which adeptly breaks down a mathematical explanation for why the rate of left-handed people has remained steady—about 10% of the population—for the last 500,000 years.

The reason boils down to two words, “competition” and “cooperation,” and how the balance between those forces plays out in human societies.

Let’s start with competition. It’s easy to see how being left-handed could give you a competitive edge in a society where fighting hand-to-hand was the only option for survival. Since most people were used to fighting right-handed opponents, lefties, despite being a minority, came to a fight with an element of surprise. As Abrams puts it, “This fighting hypothesis, where an imbalance in the population results in an advantage for left-handed fighters and athletes, is an example of negative frequency-dependent selection.”

But if it’s such an advantage, then why did lefties not increase their numbers? Why did we never break 10%? According to Abrams, evolution dictates that groups with that aforementioned negative advantage, like left-handedness, tend to grow within a population until that advantage disappears. If humans did nothing but fight each other throughout our history, lefties might have blossomed to become at least half of the population.

Which would be great! Just imagine how easy it would be to find a left-handed can opener.

But that’s not what happened. Instead, we have to take into account the second part of our equation: cooperation, aka the need to work together for the betterment of society. Cooperation requires humans to put aside their fighting impulses and do things like build tools, invent social customs, make musical instruments, and develop complex machinery. All these things put left-handed people at a disadvantage, simply by virtue of the fact that most tools are made with the right-handed majority in mind.

That’s not great for left-handed populations: As Abrams explains, “cooperative pressure pushes handed distribution in the opposite direction,” basically keeping the leftie population stable. We were 10% in the caveman days, and we’re still 10% now—and that distribution comes from competitive-cooperative effects playing out simultaneously over time.

All of which is a long-winded way of saying you should check out the video here or via the embed below. And be nice to your left-handed friends today. We only get one day a year.

Why Is It So Rare To Be Left-Handed?

If you’re left-handed, you might feel at times that the world isn’t designed with you in mind – and there’s a reason for that. Apparently only 10 per cent of the population is left-handed, which leads us to questioning why?

Most people will have what’s called a dominant hand. It’s the hand you can write with and tend to prefer to use when completing day-to-day tasks, due to it being stronger and having more dexterity (fine motor skills and coordination of the small muscles). Your dominant hand is usually determined at around 18 months old.

For 90 per cent of the population, that’s their right hand, while less than 10 per cent of people are left-handed. Even fewer are what’s called ‘ambidextrous’, meaning both their hands are equally as strong and flexible.

What causes a person to be left-handed?

It’s a bit of a mystery which scientists have a few theories about. It was once believed that handedness was linked to which hemisphere in the brain was dominant. But that one was soon dismissed because if you had a dominant side of the brain, other things that side of the brain is responsible for would also be affected.

Handedness is determined by the age of 18 months. (Credit: Unsplash/Jelleke Vanooteghem)

While a straightforward genetic link hasn’t been found, the following theories have been reported over the years as to why some people turn out to be left-handed:

• Genes – it could simply be a case of inheriting left-handed genetics from your parents. Of course, it’s also down to environmental factors and reinforcement.
• Sex – a slightly higher amount of males than females are left-handed, therefore scientists believe that testosterone could have an influence on left-handedness.
• Foetal development – Some scientists believe that handedness actually develops in the womb and that the environmental factors such as hormones during pregnancy could have a role to play.
• Modelling – no, we’re not talking about strutting your stuff down the catwalk. It’s believed that children copy things from their parents, including which hand they use. But this doesn’t explain why right-handed parents have a left-handed child.
• Brain damage – a small percentage of scientists believe in a controversial theory that all humans are meant to be right-handed, but some type of brain damage early in life causes left-handedness. If you’re left-handed and reading this, don’t be alarmed. There is no hard evidence for this theory.
• Adjustment – In some cases, people who have sustained an injury might have started out right-handed, but due to the need to adjust to an injury, they may start to use their left hand as their dominant hand.

Scientists once believed that a right-handed person had dominance on the entire right side of their body: their right eye, ear and foot – and vice versa for left-handed people.

But over the years, we’ve discovered that handedness isn’t as cut-and-dry as that. For instance, some people might be right-handed but have a dominant left foot. Others might write with their right hand, but eat in a left-handed way.

So unfortunately, there isn’t one solid explanation for why some people are left-handed. Everybody is unique, which is why it’s so difficult for scientists to pin down one theory.

What’s more, left-handedness might be a struggle at times, but there are also some advantages that come with being such a unique human being. For example, it’s been suggested that sports people who are left-handed tend to have an advantage over their right-handed opponents.

The mystery of why left-handers are so much rarer

But, Bishop says, left-handedness may be symptomatic, rather than causal.

“It’s not the left-handedness itself that’s creating problems,” she explains, “it’s more that it can be a symptom of some underlying condition. But in most people it doesn’t have any significance at all for intellectual cognitive development. ”

The debate rages on, and there is still so much we need to discover about the left-handed brain. Part of the problem is that when neuroscientists look at various aspects of behaviour, MRI studies are only done on right-handed people, in order to try and minimise the variation between different participants. Only specific studies on left-handedness will invite lefties to take part.

Since I’m currently seven months pregnant, it’s fascinating to think that my baby has already determined whether she is right- or left-handed. We know this because Peter Hepper, from Queen’s University in Belfast, has done some wonderful ultrasound studies looking at babies’ movements inside the womb.

He found that nine out of 10 foetuses preferred sucking their right thumb, mirroring the familiar pattern we see in the general population. And when he followed those children up many years later, the babies who were sucking their right thumb in the womb became right-handed, and the ones who preferred their left, stuck with that.

So, even though my baby is already favouring one hand over the other, I won’t be in on the secret until she decides to pick up those chunky crayons and start scribbling.

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What Makes Left-handed People Unique?

But while we now know that lefties are normal folks, history wasn’t always so kind to our left-handed friends. In the Middle Ages, being a leftie was enough to get you accused of being a witch, and in the 18^th and 19^th centuries, left-handed children were forced to use their right hands in schools, (which was dreadful – have you ever tried switching hands to write? It’s not easy). Those biases persisted well into the 20^th century: In the 1970s, the Soviet bloc even had official policies against lefties.

Related: 7 Surprising Ways To Become a More Creative Person

In tribute to our dear lefties and to make up for accusing them of witchcraft, here are some of their most endearing character traits.

1. They’re highly adaptable – Nearly all instruments and machines have been built by and for right-handed people. That means left-handers have had to adapt to less-than-ideal circumstances throughout their whole lives. Hats off to your flexibility, intrepid lefties!
2. They remember events better than facts – This may have to do with the way lefties use their brains, but it definitely makes their memory special.
3. Being left-handed is more common in twins – One study found that 21 percent of twins are left-handed.
4. They’re better at sports and fighting – Lefties can swing mean left hooks and can adapt quickly to unexpected situations in sports.
5. They’re not necessarily right-brained – It’s a common myth that lefties are right-brained and more creative and artistic than righties. Most right-handed and left-handed people use the left hemisphere of the brain to process language and information.

Related: 12 Things People with Glasses Can Relate To

Lefties generally lead more stressful lives because they’re existing in a world meant for right-handed people, so one way to be a better friend is to be extra accommodating. If you’re a leftie, remember that the internet has tons of stores specializing in left-handed goods. And if anyone tries to make you write with your right hand, you can just remind them about your mean left hook.

Why Are Only 10% of People Left-Handed? Here’s What Scientists Know So Far

Are you a rightie or a leftie? No, we’re not talking politics here, we’re talking handedness. And unless you happen to have an abundance of left-handed friends, you might have noticed how rare they are. So why are just 1 in 10 of us left-handed?

While no one’s been able to definitively explain this, there are plenty of hypotheses that have been building for more than a century, and the evidence points to some kind of genetic influence. Why? Because the percentage of lefties is roughly the same, anywhere you look on the globe.

For those of you who kick a ball on a regular basis, you’ll be aware that there are natural asymmetries all over the body – you’ll likely opt for one foot over the other when you go to kick.

These asymmetries can be found in everything from our feet to our ears, our eyes, and the layout of our brain, Hannah Fry explains over at BBC Future.

If you hold your thumb at arm’s length, then look at it using one eye and then the other, the eye that appears to show the thumb closest to you is your strongest. Similarly, you probably tend to answer the phone or listen behind closed doors with one ear rather than the other – that’s your strongest ear.

But why aren’t left-handed and right-handed people born to a roughly 50:50 ratio? 

Some experts suggest that social cooperation, played out over thousands of years, has given righties dominant. In other words, when communities act together – in terms of sharing tools and living spaces – using the same hand as everyone else is beneficial.

Others suggest that it’s to do with the way the brain is arranged in two hemispheres, with the left half controlling the right side of the body, and the right half controlling the left side of the body.

If most people’s brains use the left hemisphere to control intensive language and fine motor skills, the thinking goes, that bias results in the right hand being more dominant too.

In fact, one of the more unusual hypotheses to explain the rarity of left-handedness is that a genetic mutation in our distant past caused the language centres of the human brain to shift to the left hemisphere, effectively causing right-handedness to dominate, Alasdair Wilkins explains for io9 back in 2011.

And while genetics likely play a large role in determining handedness, it’s probably not the whole answer. Left-handed parents are more likely to have left-handed children than right-handed parents – a preference that can even be seen in the womb – but they still tend to have more right-handed children overall. 

Researchers have struggled to identify exactly which genes are responsible for increasing the chances of being a leftie.

In 2019, an analysis of 400,000 individual records revealed the first genetic regions associated with handedness – four of them, to be exact. But other research suggests that there are probably dozens of genes that play a role in determining whether we end up writing with our left hand or our right.

On top of that, other studies have linked factors such as oestrogen levels and birth position to varying levels of left- and right-handedness.

In short, there seem to be a lot of considerations at play, and researchers are having a hard time tying them all together. That means we can’t yet tell you exactly why you were born left or right-handed, but scientists clearly are working hard at finding an answer.

And when they do, they’ll have to explain why some of us appear to be ambidextrous, too.

A version of this article was first published in October 2016.

Are You Left-Handed? Science Still Yearns to Know Why | Office for Science and Society

Being left-handed can be devilishly hard. In 1937, an educational psychologist whose work was later discredited wrote of many left-handers that “they squint, they stammer, they shuffle and shamble, they flounder like seals out of water.” Beyond accusations of being gauche, left-handers have also had to deal with more sinister imputations. In fact, the Latin for “left” is sinister, and the left hand has historically been associated with witchcraft and devil worship. While the charges of being clumsy can often be attributed to left-handers having to put up with tools designed for right-handers, the connection to demonic powers is simply supernatural nonsense, though it is easy to imagine why left-handers—a small minority that gained invisibility as the world became more industrialized—were demonized for being different.

Once we put aside the bigotry, we are left with interesting questions. Why is it that a small subset of the population prefers to use their left hand for manual tasks, and why do we even show a preference in the first place? The body of research on these questions is a microcosm of the many challenges of doing scientific research and communicating it to the public. It’s a story of false leads, enduring myths, and hypotheses that become more and more complex as our understanding of genetics deepens.

Handing out imperfect surveys

What percentage of the population is left-handed? Sounds simple enough, but the devil is in the details. When researchers start to think about the question long enough, they realize it’s problematic. Questionnaires, like the Edinburgh Handedness Inventory, exist, sure, but some of their questions can rapidly become outdated. Ask a Millennial which hand they typically use to strike a match and you might be met with a confused face. Also, just because you write with your left hand does not mean you throw a ball with the same hand. This also brings up the issue of preference versus skill. You may prefer engaging in a manual task with your left hand, but in a test you may be revealed to be more skilled with your right hand. In fact, nearly a third of left-handed writers throw more accurately with their right hand (and a tiny percentage of right-handed writers throw best with their left).

Another kink to the story: when you ask Baby Boomers which hand they use to write, you might get deceptive numbers if your interest is in the underlying biology of handedness. That’s because for a good chunk of the twentieth century (and still in some cultures), it was common for schools to force the sinistral students to switch to the “correct” hand. Thus people born as left-handers were culturally forced to become right-handers. All of these problems have made it challenging to evaluate how common left-handedness is worldwide, with early estimates ranging from 1% to nearly 30%, but in 1994 the largest survey ever conducted and done in 32 countries provided the most reliable answer to date: 9. 5%. Nearly 1 in 10 people worldwide reported using their left hand to write, with some variation from country to country. This was somewhat confirmed by an analysis of nearly 2.4 million individuals published last year which reported a range of 9.3% to 18.1% depending on how handedness had been measured.

Left-handed humans are thus in the minority, but it didn’t have to be this way. Marsupials who hop around on their hind legs, like the prototypical kangaroo, are actually more likely to prefer their left forelimb or arm. Other animals seem to show a preference for one wing or paw over the other, but this choice is inconsistent across or within species. In having a consistent preference for the right hand, humans are quite unique in the animal kingdom to the best of our knowledge.

Sinistral preference is shrouded in its own growing mythology. Studies published over the years have seemingly shown that more left-handed people than expected are diagnosed with a large number of diseases, from autoimmune conditions to psychiatric disorders. This led scientists to wonder if common biological pathways were involved. However, as a review paper by Brandler and Paracchini pointed out in 2014, these associations are much murkier than we’d like. Often they can be traced back to an unfortunate bit of publication bias. Whether or not someone is left-handed is a quick bonus question a researcher can throw into a survey. It doesn’t cost anything. If an association is found, it gets published because it’s novel. If none appears, it’s never mentioned. This is an example of bad science and not the only one as far as handedness is concerned.

You may have heard that, on average, left-handed people die seven years younger than right-handed people. This is not true. It comes from a poorly analyzed dataset derived from a baseball encyclopedia and published in the journal Nature in 1988. An equally flawed assessment published a few years later claimed the gap was nine years. According to Professor Chris McManus’ 2019 review on the myths surrounding left-handedness, a much bigger study done using the UK Biobank in more recent years showed no difference in mortality. Yet the myth persists, in part because of its wide coverage in the media, its shock value, and its memorability.

And it’s not the only myth about handedness that refuses to die. As researchers tried to get a handle on what causes our handedness, debunked theories went on to survive like sinister zombies.

Never simple, always complex

Scientists speculated on a number of causes for left-handedness: birth complications, the use of ultrasound scanning during pregnancy, even high levels of testosterone in the fetus, which were hypothesized to disrupt normal development of the nervous system. When fetal testosterone levels could finally be measured, no association was found with handedness. A 2015 Cochrane review found no significant link between the use of ultrasound and non-right-handedness, although some argue there could be an association in male babies. As for birth complications and other claims that left-handedness is only decided at or following birth, a series of papers (summarized here) have shown that most second- and third-trimester fetuses actually suck their right thumb, and that their thumb-sucking preference, left or right, predicts whether they will become left- or right-handed. It seems that left-handedness is usually set in stone before birth. Could the brain be responsible?

When Pierre Paul Broca began to pin down where language was being processed in the brain, he found an area, now named after him, in the left side or hemisphere of the brain. So the simplistic idea was that language was processed in the left half of the brain and it would make sense, for the purpose of efficiency, for writing skills to tap into this same half of the brain. Because muscle control is contralateral, meaning that control of your right hand is actually done by the left part of the brain, it was thought that this bit of brain wiring explained why most people were right-handed. Therefore, some sort of injury must cause a minority of people to shift their language processing skills to the right half of their brain, thus making them left-handed. However, we learned through a 1999 study that things were a bit more complicated than that. Using functional magnetic resonance imaging, a team of scientists found that when right-handers were asked to silently generate words, 4% of them showed activation of both halves of their brain. Meanwhile, when studying left-handers, only 10% of them showed right hemisphere activity for this task. The vast majority of them was processing language in the left half of the brain, like most right-handed individuals. Simplistic explanations have not survived scientific scrutiny, and genetics is no exception.

As the mysteries of the DNA double helix were unspooled over the course of decades, handedness researchers wondered if this new knowledge, ever more convoluted, might explain hand preference in humans. Handedness clearly had a genetic component: it could be at least partially inherited from our parents, and so-called identical twins (who are more or less genetically identical) were more likely to share hand preference than fraternal twins (who are essentially ordinary siblings born at the same time). So the easiest bet is that there is one gene that codes for hand preference. In its wild-type form, it would make us right-handed, but mutated it would turn handedness into a coin flip. This is a version of the simplest form of heritability, the “one gene, one disease” framework, exemplified by cystic fibrosis: there is one gene, CFTR, and when both copies are mutated, you get cystic fibrosis. (As it turns out, even this model is overly simplistic, as there might be other genetic factors that modify this risk.) Researchers investigated the X chromosome, where sex-specific traits are encoded, because left-handedness skews male: for every four women who are left-handed, we find five left-handed men. It’s not a vast difference, but it was different enough that scientists wondered if X marked the spot. No dice. The mystery of why more men than women are left-handed remains unsolved.

It turns out there is no single gene that codes for handedness. In the early 2000s, genome-wide association studies—which scan the entire genome of people with and without a particular trait to see if one group has changes in their DNA that the other group doesn’t and which might potentially be causing this trait—came back negative. There was no single, one-letter change in the DNA that could reliably be tied to left-handedness. Eventually, using massive data sets issued from the UK Biobank, the International Handedness Consortium, and the direct-to-consumer service 23andMe, a team performed the largest DNA analysis for left-handedness. They found not one, not two, but 41 spots in the DNA that were associated with the trait. Handedness, like asthma and height, turns out to be a polygenic trait: many genes are involved and each makes a tiny contribution.

However, this is not the end of the story. It turns out that it’s not just the DNA that matters, but also what’s sitting on top of it. Epigenetic marks can temporarily silence bits of DNA and are generally involved in regulating when DNA is active, and these marks may have an influence on handedness as well.

Scientists have only just begun to understand the complex underlying biology of this very basic trait, and shedding light on left-handedness can hopefully blow away the superstitious and damaging myths that have long tainted people’s perceptions of a trait that can actually be advantageous. If I’m a left-handed boxer (commonly known as a southpaw), I have the element of surprise on my side. While I’m used to fighting right-handed boxers because of how common they are, they are not used to fighting me. This surprise advantage has indeed been reported in many interactive sports, like fencing, tennis, baseball and martial arts, but not in non-interactive sports, like gymnastics and swimming.

The twist is that, if left-handedness were to become more common, its advantage in a match would diminish because right-handed athletes would encounter southpaws more frequently. This is known as a frequency-selection mechanism: in this case, left-handed people gain an advantage because of how rare they are. Indeed, as we move from amateur sports to the professional leagues, we see an excess of left-handers, where the advantage that helped carry them up to the top level may start to dry up.

We have come a long way from the days when the left hand was seen as the Devil’s hand and was tied to all manner of undesirable traits. The candle of science has helped to cast these beliefs back to the shadows, although we will need much more illumination before we can fully understand the intricate ways in which handedness emerges from human biology.

Take-home message:
-Counting how many people are left-handed is more difficult than it looks, because of variations in preference and skill from task to task and because of left-handers having been forced to write with their right hand, but the best estimate we have is that roughly 10% of the world population is left-handed.
-The claim that left-handed people die younger than their right-handed counterparts is not true and comes from flawed and highly publicized studies in the 1980s and 1990s.
-There is no one gene that determines if we are left- or right-handed; rather, dozens of bits of DNA seem to make small contributions to our handedness, and epigenetic marks, which regulate the expression of our DNA, may also play a role.

@CrackedScience

Is handedness determined by genetics?: MedlinePlus Genetics

Like most aspects of human behavior, handedness is a complex trait that appears to be influenced by multiple factors, including genetics, environment, and chance.

Handedness, or hand preference, is the tendency to be more skilled and comfortable using one hand instead of the other for tasks such as writing and throwing a ball. Although the percentage varies by culture, in Western countries 85 to 90 percent of people are right-handed and 10 to 15 percent of people are left-handed. Mixed-handedness (preferring different hands for different tasks) and ambidextrousness (the ability to perform tasks equally well with either hand) are uncommon.

Hand preference begins to develop before birth. It becomes increasingly apparent in early childhood and tends to be consistent throughout life. However, little is known about its biological basis. Hand preference probably arises as part of the developmental process that differentiates the right and left sides of the body (called right-left asymmetry). More specifically, handedness appears to be related to differences between the right and left halves (hemispheres) of the brain. The right hemisphere controls movement on the left side of the body, while the left hemisphere controls movement on the right side of the body.

It was initially thought that a single gene controlled handedness. However, more recent studies suggest that multiple genes, perhaps up to 40, contribute to this trait. Each of these genes likely has a weak effect by itself, but together they play a significant role in establishing hand preference. Studies suggest that at least some of these genes help determine the overall right-left asymmetry of the body starting in the earliest stages of development.

So far, researchers have identified only a few of the many genes thought to influence handedness. For example, the PCSK6 gene has been associated with an increased likelihood of being right-handed in people with the psychiatric disorder schizophrenia. Another gene, LRRTM1, has been associated with an increased chance of being left-handed in people with dyslexia (a condition that causes difficulty with reading and spelling). It is unclear whether either of these genes is related to handedness in people without these conditions.

Studies suggest that other factors also contribute to handedness. The prenatal environment and cultural influences may play a role. Additionally, a person’s hand preference may be due partly to random variation among individuals.

Like many complex traits, handedness does not have a simple pattern of inheritance. Children of left-handed parents are more likely to be left-handed than are children of right-handed parents. However, because the overall chance of being left-handed is relatively low, most children of left-handed parents are right-handed. Identical twins are more likely than non-identical twins (or other siblings) to be either right-handed or left-handed, but many twins have opposite hand preferences.

Scientific journal articles for further reading

Armour JA, Davison A, McManus IC. Genome-wide association study of handedness excludes simple genetic models. Heredity (Edinb). 2014 Mar;112(3):221-5. doi:10.1038/hdy.2013.93. Epub 2013 Sep 25. PubMed: 24065183. Free full-text available from PubMed Central: PMC3931166.

Brandler WM, Morris AP, Evans DM, Scerri TS, Kemp JP, Timpson NJ, St Pourcain B, Smith GD, Ring SM, Stein J, Monaco AP, Talcott JB, Fisher SE, Webber C, Paracchini S. Common variants in left/right asymmetry genes and pathways are associated with relative hand skill. PLoS Genet. 2013;9(9):e1003751. doi: 10.1371/journal.pgen.1003751. Epub 2013 Sep 12. PubMed: 24068947. Free full-text available from PubMed Central: PMC3772043.

Brandler WM, Paracchini S. The genetic relationship between handedness and neurodevelopmental disorders. Trends Mol Med. 2014 Feb;20(2):83-90. doi: 10.1016/j.molmed.2013.10.008. Epub 2013 Nov 23. Review. PubMed: 24275328. Free full-text available from PubMed Central: PMC3969300

de Kovel CGF, Francks C. The molecular genetics of hand preference revisited. Sci Rep. 2019 Apr 12;9(1):5986. doi: 10.1038/s41598-019-42515-0. PubMed: 30980028; Free full-text available from PubMed Central: PMC6461639.

McManus IC, Davison A, Armour JA. Multilocus genetic models of handedness closely resemble single-locus models in explaining family data and are compatible with genome-wide association studies. Ann N Y Acad Sci. 2013 Jun;1288:48-58. doi:10.1111/nyas.12102. Epub 2013 Apr 30. PubMed: 23631511. Free full-text available from PubMed Central: PMC4298034.

90,000 Left-handed: why it is dangerous to retrain a left-hander

August 13 – International Left-Handed Day. The topic of left-handed people has always been accompanied by many myths and controversies. Some scientists talk about the giftedness of left-handers, while others insist that this feature needs to be corrected. How does a left-hander differ from a right-hander? Is it worth retraining a child if he writes with his left hand? Why is such interference dangerous? Daria Krut, a psychologist of the Game Psychotherapy Sector of the Moscow Psychological Aid Service, talks about this.

Left-handed, right-handed or ambidextrous?

Children who prefer to use only the left or only the right hand are called “pronounced left-handed” and “pronounced right-handed”. If the child mainly uses only one hand, but is able to perform the same actions with the other, they say “unexpressed left-handed”, “unexpressed right-handed.”

However, there are children who are equally good at performing any actions both with the right and with the left. They are called ambidextrous. In such situations, you can hear the recommendation: “Which hand the child uses more often, let him write.”This position is not always correct, because it is one thing to do the usual everyday activities, and another thing to write.

In the specialized literature, the concepts of “graphic functional superiority” and “everyday functional superiority” are distinguished. As a rule, “graphic left-handers” turn out to be “household left-handers”. The situation is similar for right-handers. But there are ambidextrous children both in everyday life and in graphic activities. For example, a child can almost equally use both the right and left hand in everyday activities, but it is better (more precisely, more confidently, more clearly) to perform graphic movements with the right hand or, conversely, with the left.

Are left-handed and left-handed synonyms?

In everyday life, children who most often use their left hand are called left-handed. At the same time, left-handedness can also be called left-footed, left-eared, left-eyed. The words “left-handed” and “left-handed” are often used interchangeably, but the two must be distinguished.

Left-handedness is a reflection of a certain interhemispheric asymmetry, in which the left hand is more active (leading), left-handedness means a complex characteristic reflecting the greater activity of the right hemisphere of the brain (as opposed to right-handers, in which the left hemisphere dominates).

Thus, a child can be left-handed, but not completely left-handed. If a child prefers to do everything with his left hand, it can be confidently asserted that he is left-handed, however, it is possible to say that the child is left-handed only when the leading hand, leg, eye, and ear are left-handed, which occurs extremely rare.

At what age is the dominant hand determined?

The leading hand can be determined from the age of four to five. Up to two years of age, a child experiences wave-like changes in “handedness”, and from two to four to five years of age, the hands are practically equal and equally active, and only by the age of four or five a persistent preference is formed.If you look closely at how a child unties a knot, laces up shoes, puts cubes or assembles a constructor, you can see that one hand (leading) moves actively, while the other holds the object.

Should you retrain lefties?

Parents are not recommended to retrain a left-handed child. Instead, it is better to find the right parenting methods to help solve current problems. However, it should be emphasized that it is impossible to retrain the child again, as this can lead to even more serious consequences.There are exceptions: if a child has been retrained and is used to using his right hand, but has not yet studied at school (he has no experience in systematic writing), then in this case it is not too late to change his hand. In all other cases, you will have to come to terms with unimportant handwriting and other consequences.

Why is retraining dangerous?

Retraining can negatively affect the development of the child, complicate the process of adaptation to school, and lead to serious health problems. Often, a retrained left-hander writes poorly and very slowly, makes a large number of mistakes (omissions, substitutions, mirrors letters), holds his breath when writing, squeezes the pen strongly, holds it incorrectly, his lines turn out to be uneven, the proportions of letters are violated.Reading problems may begin.

The child’s health also deteriorates: he becomes irritable, capricious, eats and sleeps poorly. Emotional disorders are often accompanied by other complications: stuttering, nervous tics, enuresis, skin diseases, obsessive movements and other mental disorders. The child begins to complain of fatigue in the right hand, headaches, decreased performance and increased fatigue, anxiety.

Having noticed these manifestations in a child (especially in a retrained left-hander), it is imperative to seek advice from a neuropsychiatric doctor or pediatrician.

Three ways to determine if a child is left-handed or right-handed

1. “Fingers entwined” – Have the child put their hands in the lock. The task should be completed quickly, without preparation. It is believed that for right-handers, the thumb of the right hand lies on top, for left-handers – the left.
2. “Pose Napoleon” – folding the arms at chest level. It is generally accepted that for right-handers, the right hand lies on top of the left forearm.
3. “Simultaneous actions of both hands” – drawing a circle, square, triangle.Leading hand movements can be slower but more accurate. The lines of the figures drawn by the leading hand are clearer, more even, tremor (hand tremor) is less pronounced, the corners are not smoothed, the connection points do not diverge.

You can also ask your child to perform simple actions: water the flowers, sprinkle the sand with a spatula, brush your teeth, push a ball with a stick, get books from the shelf, open the zipper, light a match, and so on. If the child chooses the left hand, while his movements are easier and more accurate, then the leading hand is the left.It may turn out that the child is really better at performing everyday activities with his left hand, and graphic – with his right. Or vice versa. This should also be taken into account when choosing a hand for writing.

Press Service of the Department of Labor and Social Protection of the City of Moscow

It is dangerous to retrain left-handers “on the right hand” – Rossiyskaya Gazeta

– Take pencils in your right hand! – the teacher in the garden said to the children. The right hand – it was painful to work for her children – left-handed people in very recent times!

Twenty years ago, left-handed children in our country were stubbornly retrained “on the right hand” both in kindergartens and in schools. Most were annoyed by the “unevenness” of left-handers. They were laughed at and humiliated. There were people who considered left-handedness almost ugliness.

It is not surprising that in families where a little left-handed person appeared, they began to retrain him from birth from his left hand to the right, and mothers, when breastfeeding, clamped the baby’s left hand between their own and his body, swaddled it tightly, not knowing how all this was for the baby is harmful.

And so that the grown-up kid wiped his nose and mouth with his right hand, left pockets were sewn up in his suits, a handkerchief was put only in the right pocket or pinned to the right lapel of the jacket.

Such neuroses as sleep and appetite disturbances, fears and headaches, enuresis and stuttering, irritability or lethargy, lethargy, motion sickness in transport were attributed by many doctors to age-related problems. And rarely did any of them associate these neuroses with the persistent retraining of the child – left-handed to right-handed. And now any child psychologist will give you examples on the fly when, due to the process of retraining “on the right hand”, a child with outstanding abilities lost these abilities irrevocably.

Are there any statistics on the birth of left-handers? Yes.She testifies: for parents of “left-handed” parents, the probability of having a left-handed baby is 46 percent; if one parent is left-handed – 17 percent, if parents are right-handed – 2 percent. Among the twins, left-handers are the most.

The brain knows what it is doing

Trying to make a right-hander out of a left-hander is not worth it. No teacher can change nature.

Our brain consists of two hemispheres: the right one controls the left side of the body, and the left one controls the right side. These hemispheres are unequal, one of them is the main one.If the left hemisphere is more active, the person becomes right-handed, if the dominant right hemisphere is left-handed.

The left hemisphere is responsible for speech, reading, writing, logical and analytical thinking. For right-handed people, it is dominant. The left hemisphere in right-handers controls the right arm and leg. Right – left arm and leg. For left-handers, the opposite is true. If in right-handers, when writing, as well as in most other conscious volitional actions, nerve impulses come to the leading hand directly from the left hemisphere, in left-handers these signals must pass through the bridge between the hemispheres – the so-called corpus callosum.Hence speech delays and difficulties with writing, which are more often diagnosed in left-handers. To compensate for this deficiency, left-handers develop speech centers in the right hemisphere. And this ultimately turns into an advantage: left-handers get direct verbal access to figurative information, which is operated by the right hemisphere. Perhaps that’s why jokes are better for them.

There are still many mysteries in the work of the cerebral hemispheres. By the way, the dissimilarity, asymmetry is reflected in a person’s appearance. Here’s a little test. Try, by cutting several photographs of any person’s face diagonally, create one portrait of him only from the right halves or only from the left halves. The result will be interesting – left-sided or right-sided shots of the same person will sometimes turn out to be very different from each other. In this regard, some psychologists believe that the “right” face is more like the father, the “left” – like the mother.

How are they different?

Lefties often have a strong personality.Therefore, most of them choose work related to music, painting, literature, show business, and creative professions.

Left-handed people are more prone to depression than right-handed people. Lefties are more emotional, it is difficult for them to keep themselves “within the framework”.

Left-handers tend to the humanities, and right-handers – to the exact.

“Leftists” delve into the problem faster, and do not study it sequentially, piece by piece, like right-handers, the search for a solution is intuitive. Developed intuition, which sometimes goes beyond ordinary ideas, is a characteristic feature of left-handed politicians and scientists.

And left-handed athletes? In many sports (boxing, wrestling, fencing, tennis), left-handers often create insurmountable difficulties for opponents with their original technique and emerge victorious in fights.

Who am I?

Some people are often unaware of their “leftism” themselves. It’s easy to check which part of the world’s population you belong to:

– Cross your arms over your chest. Which elbow is on top?

– Squeeze your hands with a lock, which thumb is on top?

– Try to step without thinking which leg comes forward?

– Squint as if you were shooting, the one that remained open is the leading one.

Big problems of little ones

The whole world is arranged “on the right”, so a left-handed person, until he gets used to this world, has a difficult time. From doorknobs to traffic, everything is designed for the “majority”. When right-handers, for example, cross the road, first look to the left and then to the right. For left-handers, everything is different, they look to the right, and only then they look to the left. Parents must take into account all these features when they teach their baby the rules of the road.

By the way, the left-handed kid is trying to read from right to left. Therefore, it will take time and patience to teach him to perceive the text.

Another problem of the little left-hander is orientation by the clock: it is more difficult for him than for the right-hander to remember the direction of the arrows.

Children, as you know, learn from the example of their parents: mother peels potatoes, sews, and daughter watches and repeats her movements, learns. In the case of a left-handed person, this option does not work. The child does not understand how to do the same, but with his left hand.

So the left-hander has to learn a lot by trial and error. Although this, of course, slows down the learning process, but you should not be upset. All this does not mean at all that your baby is “wrong”. He is absolutely normal, like other children, only perceives the world in his own way.

If you are in doubt if your baby is right or left handed, do the test. Ask your toddler to wipe the table and see which hand he takes the rag in. In this case, in no case say why exactly he should do what you ask.Let him perceive what is happening as a game. Otherwise, knowing that you are determining, for example, which is the “leading” eye of the baby, the child can consciously bring the tube instead of the right eye to the left. And after that, it will be very difficult to lull his vigilance in order to carry out the experiment again.

Remember the main thing: a left-handed person should never be retrained. It’s like teaching a person to walk not on their feet, but on their hands. But the child’s left hand should definitely be developed – because sometimes the leading hand of the baby develops poorly:

– Offer to tie and untie knots. Left hand, of course:

– Let him collect puzzles or lay out mosaics from pebbles;

– It is useful to assemble-disassemble, spin-spin small parts;

– The best workout is to twist and twirl a pencil in your hand.

HANDS ARE OUT THEREOUS – Spark No. 3 (4729) dated 27.01.2002

It may seem very strange, but the number of left-handers in our country, according to sociologists, has almost tripled over the past hundred years! In our country, every fourth citizen is left-handed, and in some regions of the country – every third! And the number of left-handers is growing steadily.In America, almost a third of the nation is left-handed; of the last four American presidents, three (Bill Clinton, George W. Bush, Ronald Reagan) were left-handed. What kind of attack? Today we present two opinions on this issue – psychologist Vladimir LEVI and geneticist with physical education Vigen GEODAKYAN

HANDS ARE OUT OF THERE

Vladimir LEVI: “A patient came to me the day before yesterday by the name of Sobakin. It happens. However, the next was a patient named Kobelev. I was already on my guard.And on you: Today Suchkin is still there … It’s just a coincidence. ” The diaspora of left-handers is becoming more and more numerous. Are we mutating? Or is this a normal stage in human development?

– By the way, I myself am not quite right-handed, but half-left-handed – the so-called ambidexter: I can write with my left hand, I draw equally with both, I play the piano equally fluently; while boxing, he had a signature left hook, and when he played football, he preferred to kick on goal with his left foot rather than his right foot.

Nevertheless, there is still no reliable scientific evidence of the actual progression of “left-handedness” and, as I believe, there will not be. It’s just that left-handers began to express themselves more freely as left-handers, so it began to seem that there are more of them. The world is becoming more free, and what was previously hidden or not noticed, now creeps out. It’s not just left-handed people. In the same proportion, for example, the number of “sexy left-handers” – the so-called gays and others like them, has increased. All thanks to the greater freedom of expression and self-affirmation.

– But there is evidence that the number of left-handers in the regions of the country is extremely heterogeneous. For some reason, the maximum number of left-handers (about 30%) is concentrated in the Taimyr Autonomous Okrug and in the Far East.

– I am inclined to believe that the heterogeneity of left-handers across regions is more likely due to random variation in survey methods. Genetic-population variations are also possible: perhaps, among the first settlers of Taimyr and Vladivostok, there were by chance a little more actively breeding left-handers… By the way, the same regional variations, which at first glance seem obscure, exist, for example, in the distribution of genetic blood groups. And everything is explained in the same biological and historical way, like the spread of any other properties, up to and including the shape of the bald head.

– What makes a person to be left-handed?

– Her Majesty Nature. The laws of genetics first of all, as well as the laws of the structure of molecules, the laws of chemistry. After all, there are left-handers not only in the world of living organisms, but also in dead matter.Molecules of the same organic matter are “dextrorotatory” and “levorotatory”. At the same time, there is always a stable quantitative proportion: the “right” molecules in any substance are in the majority, about four-fifths. And the rest are “leftists.” The same proportion is between right-handers and left-handers! Here it is, the true deep-natural basis of “left-handedness”, mysterious in itself, but obvious and indisputable.

And this is not only for humans, by the way: for all living creatures without exception. There are left-handed monkeys, left-handed birds, left-handed fish, left-handed plants, left-handed bacteria, and viruses…

– Why are there so many left-handers in America? After all, the percentage of left-handers there is consistently high. Maybe left-handers reproduce faster in good conditions?

– The high percentage of left-handed people in America is not associated with increased fertility, but with free detection. There are as many left-handers in America as there should and can be by nature. There can never be more than one left-hander for every four or five right-handers.

– Is it an accident that almost all presidents have been ruling the country over the past decades?

– There is a persistent statistical-probabilistic law in the world – the concentration of rare events.Came to me the day before yesterday, for example, a patient named Sobakin. Well Sobakin, so what? It happens. However, the next was a patient named Kobelev. I was already on my guard. And on you: today Suchkin is still appearing, believe it or not, such a mysticism. And so it turns out, if you look closely, in everything – rare events and rare signs come in clusters.

In addition, there are many transitional degrees between pure right-handedness and pure left-handedness – there are, as my example shows, people of double spatiality… It is very likely that in early childhood there is a certain amount of “freedom of choice” for those who are genetically indeterminate, duality, like me – such a child is prompted and imposed by the “right” society which orientation to choose. The choice is fixed by habit.

– They say lefties are more talented.

– They say “blue” too. Lefties are not the best part of humanity, but just a mirror. She is simply forced to live more tensely and volitionally, more attentively and concentratedly.Only because the world is not arranged for them – the world is spatially against them. Lefties are forced to live more intensively, more adaptively, more flexible, so their percentage at the top of the ladder of success is noticeably increased.

Take other human minorities – sexual or some national ones, also forced to live under the press of restrictions and violent suppression of their essence. After all, both among the “gays” and among the short ones, the percentage of social success in many areas is also increased: in art, in pedagogy, in show business, in the press, advertising, and politics…

Or, say, Jewish talent – financial, scientific, administrative, chess, etc. Do you think this is what – the genes of the Jews are like that? No, the result of pressure from an aggressive environment. The fruit of historical anti-Semitism, a centuries-old heightened need to think, think, survive and turn around. Therefore, by the way, these national talents in Israel, where anti-Semitism by definition does not exist, happily sour and die. Today’s Israel has not yet presented the world with a single large-scale genius, and I am afraid it will not give it soon, because a Jew in Israel is no longer socially “left”, but “right” and, alas, this does not benefit his mental development…

So the world is not threatened yet by a global disease! And even if left-handers suddenly, on one terrible left day, fill our entire ball, nothing good or bad will happen. Well, left-handers do not have any other values, besides those of many sinful right-handers; there is no special view of the world, believe me. Just like redheads.

But here is what can be predicted with a high probability: the number of “right-wing leaders”, that is, ambidexters, will increase on earth. The genetic tendency of the human species is to become more and more open and diverse, less and less fixated on any one way of being.We must be different, we must be different – otherwise the skiff …

– In recent days, I am tormented by one question. Why does Putin wear a watch on his right hand? Is he really too? ..

– I also closely observe Vladimir Vladimirovich from the point of view of pravism-levism and note that he gestures mostly with his left hand. But he greets strictly according to the ritual – right. True, somehow slightly distant, as if slightly detached from his right hand, he greets – not bringing it closer, but removing the face and body from the interlocutor.This leads to the suspicion that maybe it would be more comfortable for him to say hello with his left, but the image does not allow. Maybe the president is also an ambidexter?

– Vigen Artavazdovich, the Academy of Sciences told me that you are one of the world’s largest experts in the field of “left-handedness”. So tell me, has science already established what a left-handed person is and what is it for?

– Unfortunately, science thinks nothing, oddly enough. And I have several theories on this score. I myself am not a native biologist, I was a physicist in my youth, but I went crazy with biology in time and began to deal with these problems.My first theory – you may have come across it – is the theory of sex. My idea was that the male sex is experimental.

I came up with the theory of binary conjugate systems. What it is? Let me explain now … The population is divided into two sexes, the human genome is divided into autosomes and genosomes. The brain is divided into two hemispheres, society – into left-handers, right-handers, and so on, on, on. There are a lot of such binary, but inseparably existing systems in nature. So, the point is that any evolving systems are always divided into two coupled subsystems that work on two main aspects of evolution – preserving what has been achieved and changing it for the better.This is how the systems increase their stability.

Five years ago, the famous Japanese explorer Doreen Kimura made a discovery. There are two diseases – aphasia (speech disorder) and apraxia (movement disorder). So, if women are sick with these diseases, then they have it due to damage to the frontal parts. If men are sick – with the back of the brain. And since the male sex is the vanguard, which is evolutionarily ahead of the female sex, it turns out that in men this function has already gone to the occipital part of the brain, while in women it has not yet.After all, skill centers appear in the brain and move in the course of evolution from left to right and from the forehead to the back of the head. Judging by indirect data, women lag behind men evolutionarily by about five hundred years. Not less.

In 1990 attended the European Congress of Anthropologists. One Bulgarian presented her work there, she studied dermatoglyphics, drawings on fingers. She researched Bulgarians and Bulgarians and compared them with neighboring ethnic groups. It turned out that the pictures of Bulgarian men and Turkish men stand side by side in her diagram, and the points of Bulgarians are very far from them.Bulgarian men and women are very far from each other. She, however, could not explain it in any way, I helped her. It is known that the Turkish yoke was about five hundred years ago. This means that the Turkish genes came to the Bulgarians just then. And during this time, having entrenched themselves in males, they have not yet switched to the Bulgarians.

– That is, the information has already entered the male gene sets, genes, but has not yet passed into the female? And then it will move?

– In the future, yes. The new gene enters the male genome.It has special mechanisms where he undergoes quarantine service, sits in isolation. These genes should not get to the female sex ahead of time, until they are tested in the male genome.

The male Y chromosome is the gateway to heredity variation. And there are special mechanisms through which the gene must pass until it reaches the female X chromosome. That is, each chromosome should have, as it were, a landing strip and a take-off strip. First, a new gene lands at one end of the male chromosome, then for a long time moves to the other, takeoff.And until the gene jumps to this strip, it cannot get into the neighboring chromosome. By the way, it has long been known that genes jump from place to place. But no one knew where they were jumping and why.

– How does it work in nature?

– Look … At first, there is no sign – zero. For example, there is no tail, the species is tailless. Time passes, conditions change – a tail is needed. This tail initially appears only in males; females remain tailless. Stay for a long time! In males, it lengthens, lengthens, at this time the tail genes are quarantined and finally reach the female sex.Women have a tail. It appears and also lengthens a little. As a result, the species became completely tailed. Then this sign suddenly turned out to be unnecessary. First, it is shortened in males, disappears, then disappears with great delay in females.

– And what does the left-hander have to do with it?

– Lefties are also an experimental squad, an analogue of the male sex, only at the cultural level. What gender does at the genetic level is exactly what lefties do at the cultural, mental level.They allow the nation to change more actively, to adapt to difficult critical conditions.

Therefore, I can firmly predict an increase in the percentage of left-handers in all cases of environmental and mental stress and discomfort: among interracial, interethnic hybrids, in alpine, seismic, ecologically unfavorable areas, after earthquakes, wars, genocide, hunger, resettlement and other social and natural shifts – in all cases when the birth rate and mortality rate of the male increase.For example, a sharp drop in the average life expectancy of men in comparison with women should be accompanied by a simultaneous increase in the birth rate of boys and left-handers.

And new functions, which left-handers easily mastered, pass in the next generations into right-handers, into the cultural blood of the nation. German scientists conducted research in African tribes. We watched what and how the cannibals were doing. For non-instrumental (animal) functions with the right hand, they worked in 54% of cases. And for instrumental (reasonable) – in 84% of cases! Right hand, i.e.e. the left hemisphere!

Then I began to study monkeys. The monkey grabs the fetus with his left hand. But she opens the latch and dials the phone number (if she is trained to do this) – right. As you know, the right hand is controlled by the left hemisphere, and vice versa. So, if the working function is very ancient, for example, to take a fruit in his hand for eating, the monkey will take it with his left hand, that is, with his “right hemisphere”. Because the right is conservative. And the left one is “exploratory”, search, it will try out everything new, and the right one is saved for posterity in the form of reflexes.

– And what does the left-hander have to do with it?

– I’ll explain now. A newborn baby has a grasping reflex. The reflex is an ancient thing, recorded in the right hemisphere, which is responsible for the left hand. Therefore, the child grabs everything with his left hand. Further.

Fifteen years ago, they discovered that the right ear is more sensitive to semantic sounds, and the left is more sensitive to natural, environmental sounds. Now the eyes … Take a simple flash of light (lightning) and semantic pictures (words).It turns out that the flash is better captured in the left field of view, and words, numbers, portraits – in the right. Next is the sense of smell. Since a person’s sense of smell is an atavistic, disappearing function, it should be better developed in women than in men. And of course the left nostril smells better than the right.

The key to the riddle of asymmetry lies in the control scheme of paired organs by the hemispheres of the brain. Left-handedness is identical with one sex, right-handedness with the other. Left-handers are an operational subsystem, analogous to the male sex, and right-handers are a conservative subsystem, analogous to the female.This means that evolutionary innovations must first appear in the right organs of left-handers, and then end up in the right organs of right-handers. There should be mechanisms that change behavioral signs: ensuring that information is received from the environment by the left-hander’s right hand and further reaching the right-handed person’s right hand. Just as differentiation into two sexes provides the species with informational contact with the environment for the effective evolution of hereditary traits, so the differentiation of society into right-handed and left-handed people does the same for the behavioral traits of the psyche.

Dmitry AKSENOV

Photos used in the material: Lev Sherstennikov
90,000 How do left-handers live in a right-handed world?

“Why are you cutting crooked? Why are you holding the pen so strangely? Do you even see what you wrote? ”

How often have you heard such questions? If it is rare, then perhaps you have asked such a question at least once. To whom? Lefties, of course!

Depending on the region, the number of left-handers on the planet ranges from 15-17 percent.Despite the relatively large percentage, the world is still created for right-handed people, and left-handers have to adjust and “mirror” reality. From time immemorial, left-handers were discriminated against, but even centuries later, in the 21st century, they experience certain everyday difficulties:

• they are forced to sit on the left side of their interlocutor for the convenience of writing;
• Doors cannot be opened with the left hand;
• Most tools are designed for right-handers and are deadly in the hands of left-handers.

And this is not a complete list. Unfortunately, special products for left-handers are also not always convenient.

There are many secrets and prejudices about what determines our left- or right-handedness, and why left-handers are a minority.

Among children of right-handed parents, left-handers make up about two percent, if one parent is right-handed – 17 percent, for two left-handed parents, the probability increases to 46 percent. However, not only people are left-handed: cats are left-handed in 54 percent of cases, mice in 44 percent, two-thirds of chimpanzees prefer to take food with their left hand, and polar bears are completely left-footed.

Scientists have long debated how left-handedness is related to brain function. The left hand is controlled by the right hemisphere of the brain, and vice versa, so left-handed people may have a slightly different brain structure. Because of this, left-handers are credited with excessive emotionality, a penchant for creativity and high mental abilities. Left-handed people manage to achieve high results not only in creativity and the exact sciences, but also in sports. For example, in boxing, fencing or hand-to-hand combat, where left-handers have a significant “surprise factor” in defense and attack.

There are many outstanding scientists, athletes and artists among left-handers. But talented left-handers live not only in textbooks or TV screens, they live among us. We talked with the left-handers of Arkhangelsk and learned about their lives.

Eugene, DJ:

“As a child, the only difficulty was that it was inconvenient to write in notebooks with a spring. And the hand from the pens got dirty. But they didn’t try to retrain me. It seems to me that I help myself with my right hand in the same way as the right-hander helps with the left, maybe a little more.I did not use products for left-handers, I always either adjusted with the left, or accustomed to the right. Well, left-handedness does not affect the work of a DJ at all. ”

Anastasia, NArFU student about her father:

“Dad repairs radio stations, solders everything. Can do it with both right and left hand. For example, he holds a spoon with his right, and cuts bread with his left, but writes only with his left hand. The school was treated normally, no one teased. The only thing that the first teacher in primary school retrained him, shifted the pen to his right hand, but, according to my father, as soon as she turned away, he shifted to the left again, and never retrained.

Kirill, musician:

“There were no particular difficulties in childhood. Once my parents bought a special spoon for left-handers, but I found it inconvenient to use it. And at school I always had to sit on the left so as not to push my hands with my neighbor on the desk. In the same way, almost always, when writing, the paste was “smeared”, so it was impossible to write with gel pens. I noticed that I hold my phone with my right hand and control the mouse, and I do everything else with my left. I play the guitar like a right-hander, that is, with my left hand I grip the strings on the fretboard, and with my right I pluck the strings.The left hand is more resilient, so it gets less tired, and I can press the strings to the neck harder. ”

Nature loves to complicate things no less than people: it turns out that 100% left-handers do not exist, right-handers can be hidden left-handers, and natural ambidexters (who have the same right and left hand) are generally a rarity. Research shows that humans have predominant body organs such as the eye, leg, and ear, regardless of the “dominant” hand.

There are many tests for determining the leading parts of the body.We offer a simple test to determine if you are left-handed, right-handed, or equally good at using both hands.

• Which hand do you usually write with?
• Which hand do you draw with?
• Which hand do you throw the ball with?
• Which hand do you hold the tennis racket?
• Which hand are you holding the toothbrush in?
• Which hand do you hold the knife in when you cut something (without a fork)?
• Which hand do you hold the hammer in when you hammer in the nails?
• When you light a match, which hand is holding it? Which hand do you use the eraser with?
• Which hand do you take off the top card of the deck?
• Which hand are you threading the needle with?
• Which hand do you hold the fly swatter in?

Evaluate the answers as follows: “left” – one point, “all the same” – two points, “right” – three points.Now let’s calculate the results: 33-36 = Absolute right-hander

• from 29 to 32 – right-handed;
• from 25 to 28 – almost right-handed;
• 24 – ambidextrous;
• from 20 to 23 – almost left-handed;
• from 16 to 19 – left-handed;
• from 12 to 15 – absolute left-hander.

Whatever the result of the express test, it is important to listen to yourself and appreciate your own uniqueness, regardless of the hand with which you write.

Can a dentist be left-handed?

There is an opinion that a dentist cannot be left-handed.If desired, a person is recommended to retrain to work with the right hand. However, it is important to understand that retraining is not an option. In addition, retraining is quite harmful to the body. But what can you do in this case if you don’t want to give up your dream? Fortunately, modern dentistry has a huge number of left-handed doctors. For their successful work, special equipment was invented, most of the equipment is fully adapted for use by both the right and left hand.The only problem is possible only in the course of the learning process, because all materials and techniques are focused on right-handed use. Also, many specialists with a similar feature in the future are looking for left-handed assistants, since it is much more comfortable for them to work together.

Statistics

There are more and more left-handers in the world every year, especially over the past 10 years. There are over 500 million such people in the world today. It is worth noting that they choose very different professions.In every field of activity, you can find at least a few left-handed craftsmen, whose work is in demand and has many positive reviews.

From a scientific point of view, the appearance of left-handers is not justified in any way. There is no particular “left-handed” gene, but families rarely have just one left-handed person. Scientists have come to the conclusion that such people are incredibly talented and gifted, they achieve success in everything they undertake. Also, left-handers have some characteristics that are unique to them.

Of course, our life is arranged in such a way that almost everything is adapted for the comfortable life of right-handed people. This leads to the fact that all other people often have difficulties with adaptation in society. But do not despair, as conditions are getting better every year. The same is the case with the profession of a dentist: special tools are developed for left-handed people, new methods of work appear.

Special feature of the dentist’s work

The activity of dentists is inextricably linked with the performance of many precise manipulations, during which there is no room for error.That is why for the effective work of a left-handed dentist, it is necessary to create such conditions under which he will feel as relaxed and confident as possible.

To perform the work, instruments and equipment adapted for the left hand are required. In the office of such a master there should be a comfortable chair, and his chair should be located on the left. Modern manufacturers offer special dental chairs with several counterclockwise positions. Also, a drill and other devices often used in the course of treatment should be installed on the left.

An important point is that long-term work on the equipment, which is intended for right-handed doctors, can negatively affect not only the quality of treatment, but also the well-being of a specialist. As a result, he may be diagnosed with early osteochondrosis, disorders of the nervous system, etc.

Basic rules of work

In order for the activity of a left-handed dentist to be as effective as possible and not further affect his own health, some recommendations should be followed.It is very important that vocational guidance of applicants is carried out in higher educational institutions. This is required in order to determine in advance the possibility of a future specialist working in his chosen field.

For left-handed students who are already undergoing training, their training and workplace must be properly organized. In the process of training, there should be no inconveniences, because this can lead to the loss of any desire to do your job.

The work of the master should take place only on universal equipment, which is equally convenient for both right-handed and left-handed people.This ensures that the best treatment results are achieved without harm to health. Today, such people can count on all the necessary conditions, so you should not give up your favorite activity because of the existing physiological characteristics.

Convenience of modern equipment

Absolutely all equipment that was used more than 10-20 years ago was designed for the classic grip, that is, with the right hand. Everyone else had to go through lengthy retraining.

Fortunately for all those who today want to become a highly qualified dentist, there is no longer any point in retraining a person, because it is much easier to “retrain” equipment. Most professional work accessories are easily transformed. For example, the blocks of the doctor and assistant in them can be moved from side to side, this makes it possible to be both to the right and to the left of the patient.

The same applies to the valve body, it can be easily moved to the desired position.Additionally, the console can move in a vertical plane, which simplifies the work of small doctors. Nowadays, nothing prevents the development and formation of dental masters, even if their left hand is the worker.

90,000 what is really wrong with them – Rambler / Saturday

Almost the entire population of the planet begins to move with the right foot and it is with the right hand that they write and draw. At the same time, in every country, that is, among all peoples, left-handers are born too, but there are much fewer of them in percentage terms.Why do right-handers dominate human nature?

Left-handedness is a rare side effect

As you know, the left hemisphere is responsible for the work of the right arm and leg, and the right side of the brain is responsible for the work of the left limbs. The speech center, coordination of movements, ingenuity and the use of experience and memory are located in the neural regions of the brain, also located on the left side of the skull. At the beginning of our century, American anthropological historians found out that even one and a half million years ago, representatives of the species that preceded modern man, at the time of the first movements on two legs and the use of primitive speech, began to use one hand to a greater extent – the right, because the development of all skills is connected with increased work of the left hemisphere.But left-handers were born then and live today, but they are not inept or to some extent underdeveloped people. The speech center and all other important neural connections are also located in the left hemisphere. This was confirmed back in the 1950s by the Japanese physician Chon Wada, who revealed this using a special technique. He used a test that surgeons sometimes carry out in preparation for brain surgery, which reveals the belonging of certain neuro-functions to a particular hemisphere.During the tests, an anesthetic drug was injected into one of the carotid arteries of each subject, which blocked a specific hemisphere of his brain for several minutes. As a result, after turning off the left hemisphere, 90% of right-handers stopped working their right hand and could not speak. However, 70% of left-handers also lost their speech and the ability to move their right hand when the left hemisphere was turned off. In other words, their neural connection works in the same way as in right-handers, and the dominance of their left hand is just an accidental side effect that is extremely rare in some individuals.That is why right-handed people prevail on the planet.

Not a predominant combination of genes

However, renowned psychologist Chris McManus of University College London, UK, believes that the birth of left-handers is encoded in human genes. In his book Right Hand, Left Hand, he cites the facts that left-handers have different principles of the functional organization of the brain. And a single gene is responsible for such a development of a person, which can be of two varieties: dextral (D) and chance (C).Dextral forms right-handedness, and chance adds variability. The combination of the parents’ genes determines whether the child will be right-handed or left-handed: DD is 100% right-handed, CC is left-handed, but with a probability of 50%, and CD is a possible left-handed person, but only by 25%. From this combination, it becomes clear that, as a percentage, more right-handers are born than left-handers. Therefore, according to statistics, every seventh person in the world is left-handed. In 1977, approximately 8-15% of the world’s adult population was left-handed.But why? Do they appear after all?

Hormonal failure in the womb

All left-handers also acquire knowledge and professions, live in the same society, but use their left hand to a greater extent. And this is their whole difference. However, doctors from the National Medical Research Center for Children’s Health, Russia, have long found out that left-handedness in babies manifests itself simultaneously with the development of speech, and it is at this moment that its defects are noticeable. Left-handed children perceive the world the other way around and voice it, for example, as not “Aunt Tanya”, but “Tanya Aunt”.And although they are taught to write from left to right, they initially perform math functions from right to left, so standard training is more difficult for them than for right-handers. But these are not all the differences. Since statistics claim that men are more often born left-handed than women, American neuropathologist Norman Geshwind found out another pattern. Higher testosterone levels in the womb increase the likelihood that her baby will be left-handed as well as a boy. Testosterone affects the rate of prenatal growth of the hemispheres of the developing fetal brain and is responsible for possible differences in brain structure in both men and women.High testosterone levels during intrauterine development slows down the growth of the left hemisphere in the male fetus compared to the female and contributes to the relatively greater development of the right hemisphere. If in the left hemisphere of the developing brain the process of migration of neurons to the places of their final placement slows down, then such a delay can lead to left-handedness. Geshwind believes that along with this phenomenon, the development of the fetal immune system is also inhibited. Therefore, left-handers, both men and women, often suffer from various infectious diseases.However, such hormonal disruptions in pregnant women are not such a frequent occurrence, which is why much less left-handed people are born in the world.

Neuropsychologists have debunked common myths about left-handers

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Neuropsychologists have debunked common myths about left-handers

Neuropsychologists have debunked common myths about lefties. common myths about left-handed people

Many common myths about left-handed people do not correspond to reality, experts interviewed by RIA Novosti told RIA Novosti on the occasion of the International Day of Left-handers, RIA Novosti, 13.08.2019

2019-08-13T10: 06

2019-08-13T10: 06

2019-08-13T15: 29

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MOSCOW, August 13 – RIA Novosti. Many common myths about left-handed people do not correspond to reality, experts interviewed by RIA Novosti told RIA Novosti on the occasion of the International Left-Handed Day, which is celebrated on 13 August.As the neuropsychologist, head of the NeuroPraktik center Yulia Punina said, the society has always treated the left-handers with ambiguity. The ancient Greeks considered them a special caste, close to the gods, and in medieval Europe, on the contrary, left-handers were burned at the stake as messengers of the devil, in Soviet times there was an opinion that they needed to be retrained. Only closer to the 20th century, scientific research began to be carried out on this topic. Sometimes scientists argued that left-handedness is a pathology or that people with such a feature are prone to commit crimes, and towards the end of the century, all left-handed people began to ascribe a special talent or predisposition to creativity.Left-handedness is a deviation from the norm According to neuropsychologist Natalia Semyonova, a member of the Russian League of Psychiatrists, Psychologists and Psychotherapists, left-handedness is not a deviation from the norm, it is inherent in nature. According to her, 40% of people are genetically left-handed, that is, it is inherited. during an ultrasound examination, it is possible to determine whether a child will be right-handed or left-handed by the finger of which hand sucks the fetus, says neuropsychologist Punina. “According to various studies, the chances of having a left-handed parent are up to thirty percent, while right-handed parents are within ten percent. “, – she said.However, according to her, one cannot say that this is absolutely true. For example, it so happens that in a pair of monozygotic (identical) twins, one is right-handed and the other is left-handed. “Genetics in this case just increases the chances,” said the neuropsychologist. Also, according to her, there is also compensatory left-handedness, when the child is in At an early age, it injures the leading right hand and begins to use the left. Premature babies are more likely to become left-handed. In addition, among the reasons why a child becomes left-handed, neuropsychologists interviewed by RIA Novosti name some pathologies during childbirth.However, Punina notes that there is no direct connection between prematurity and the development of left-handedness. But there is evidence that there are more left-handers among premature babies and children born to mothers over 40 years old. At the same time, experts interviewed by RIA Novosti unanimously argue that whatever the reasons for left-handedness, it is not worth retraining a child. We can influence it We can promote the development of the left hemisphere by retraining the child on the right hand, but we cannot change his genetic program.If a child has a pathology … the child is only more or less trying to compensate due to his pathologies, and we start to intervene, “Semenova noted. Punina believes that if a child is forcibly retrained, it is possible to cause to nervous breakdowns, stuttering and enuresis. Lefties are more talented and creative As neuropsychologists note, the opinion about the creative predisposition of left-handers is due to the fact that the right hemisphere of the brain, which controls the left hand, is responsible for imaginative and spatial intelligence, while the left hemisphere is responsible for logic.At the same time, as Punina notes, these statements are erroneous. “Left-handedness does not at all mean the dominance of the right hemisphere, many mental functions in left-handers can be controlled by the leading left hemisphere,” she noted. According to her, among outstanding personalities in science and art, indeed, a large number of left-handed people, but their number nevertheless does not exceed the same category among right-handers. “So there is no reliable data and proven research on the intellectual and creative superiority between right-handed and left-handed people today,” concluded Punina.Lefties have fragile health and often get sick According to Semenova, left-handers can really get sick more often. This is due to the fact that in the early stages of development, they may experience stress, trying to adapt to the “right-handed world.” In addition, according to the neuropsychologist, the right hemisphere is more sensitive. Therefore, left-handed people are more susceptible, including to disease. Punina, in turn, noted that there were attempts to correlate left-handedness and the risk of Crohn’s disease, schizophrenia and breast cancer.”Studies have shown a large percentage of left-handers among the sample. But so far these theories have not received enough confirmation,” she said. have a tendency to addictions. “There is such a thing as addiction: alcohol, tobacco smoking, gambling addiction, drugs, codependency on another person. This is typical for left-handers, due to the fact that if the left hemisphere is more logical, intellectually programmable: goal, rules , the laws.And the right one is a little chaotic, multivariate, “she said. According to her, since left-handers have to adapt from childhood, it is quite difficult for them.

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MOSCOW, Aug 13 – RIA Novosti. Many common myths about left-handed people do not correspond to reality, experts interviewed by RIA Novosti told RIA Novosti on the occasion of the International Left-Handed Day, which is celebrated on August 13.

According to the neuropsychologist, head of the NeuroPraktik center Yulia Punina, the society has always been ambivalent about the left-handers.

The ancient Greeks considered them a special caste, close to the gods, and in medieval Europe, on the contrary, left-handers were burned at the stake as messengers of the devil, in Soviet times it was believed that they needed to be retrained.

Only closer to the 20th century, scientific research began to be carried out on this topic. Sometimes scientists argued that left-handedness is a pathology or that people with such a feature are prone to commit crimes, and towards the end of the century, all left-handed people began to ascribe a special talent or predisposition to creativity.

13 August 2019, 03:00

Experts told why lefties are more successful than right-handed norms, it is laid down by nature.

“There are also left-handed animals, for example, a polar bear. This is the diversity of nature for survival, it is a genetically programmed thing,” she said.

According to her, 40% of people are genetically left-handed, that is, it was passed on to them by inheritance.

Often, during an ultrasound examination, it is possible to determine whether a child will be right-handed or left-handed by the finger of which hand sucks the fetus, says neuropsychologist Punina.

“According to various studies, the chances of having a left-handed parent are up to thirty percent, while those of right-handed parents are within ten,” she said.

However, according to her, it cannot be said that this is absolutely true. For example, it happens that in a pair of monozygotic (identical) twins, one is right-handed and the other is left-handed.

“Genetics in this case just increases the chances,” said the neuropsychologist.

Also, according to her, there is also compensatory left-handedness, when a child at an early age injures his leading right hand and begins to use his left.

13 August 2018, 15:20

Starry Day of the Left Handed International Day of the Left is celebrated every year on 13 August.Since ancient times, such people were surrounded by myths: left-handedness was considered a sign of either inferiority or genius. Psychologists say that the brain of left-handers works in a special way, there is no automatism in their actions, this is the secret of creative activity. Celebrities left-handed – in the Ria.ru photo feed.

Premature babies are more likely to become left-handed

In addition, among the reasons why a child becomes left-handed, neuropsychologists interviewed by RIA Novosti name some pathologies during childbirth.

However, Punina notes that there is no direct connection between prematurity and the development of left-handedness.But there is evidence that there are more left-handers among premature babies and children born to mothers over 40 years old.

At the same time, experts interviewed by RIA Novosti unanimously argue that whatever the reasons for left-handedness, it is not worth retraining a child.

“By retraining the hand, we do not change the brain. We can influence it. We can promote the development of the left hemisphere by retraining the child on the right hand, but we cannot change his genetic program. If the child has a pathology … the child only more or less tries compensate for our pathologies, and we begin to intervene, “Semenova noted.

Punina believes that if you forcibly start retraining a child, you can cause a psychophysiological failure, which, in turn, leads to nervous breakdowns, stuttering and enuresis.

August 13, 2017, 08:00 Science “Left” among us: what is the difference between the brain of right-handers and left-handers

Lefties are more talented and creative

the left hand is responsible for imaginative and spatial intelligence, while the left hemisphere is responsible for logic.

Moreover, as noted by Punina, these statements are erroneous.

“Left-handedness does not mean dominance of the right hemisphere, many mental functions in left-handed people can be controlled by the dominant left hemisphere,” she said.

According to her, there are indeed a large number of left-handed people among outstanding personalities in science and art, but their number nevertheless does not exceed the same category among right-handers.

“So there is no reliable data and proven research on the intellectual and creative superiority between right-handed and left-handed people today,” Punina summed up.

June 19, 2015 11:28 not right-handed like people.

Lefties have fragile health and often get sick

According to Semenova, left-handers can really get sick more often. This is due to the fact that in the early stages of development, they may experience stress, trying to adapt to the “right-handed world”.

“When a child develops, these loads can undermine his autonomic nervous system, so he can get sick,” she said.

In addition, according to the neuropsychologist, the right hemisphere is more sensitive. Therefore, left-handers are more susceptible, including to diseases.