BBC Future columnist talks about the amazing things scientists who study right-handers and left-handers are learning.
We learn about whether we are right-handed or left-handed in childhood, when we take a pencil and start drawing our first scribbles.
But what makes one of our hands dominant? And why are lefties in the minority?
To solve this mystery, Adam Rutherford and I decided to delve into the history of the issue and get the opinion of scientists, and then talk about it in the BBC Radio 4 show "Curious Cases of Rutherford & Fry" (The Curious Cases of Rutherford & Fry).
It soon became clear that this topic was much deeper than we thought: for example, I did not even suspect that not only the hand could be the leader. This applies in particular to the eyes.
You can check which eye dominates you as follows.
Extend your hand in front of you with your thumb up. First look at the finger with both eyes, and then close the left and right eyes alternately. The leading eye is the one that gives the picture closest to what you see with both eyes.
Likewise, you can test your ears: which one do you usually hold your phone with? And which ear will you put to the wall to overhear what is being said in the next room?
Promotional video:
Overall, 40% of us are left-eared and 30% are left-eyed
It's funny to see this strange asymmetry in your own actions. For example, I often hold the phone with my left hand, and rather awkwardly try to press it to my right ear while writing with my right hand.
This strange combination can hardly be called convenient. However, in this case, this is not the main thing - the whole point is that we strive to use the advantages given to us by nature.
Overall, 40% of us are left-eared, 30% are left-eyed, and 20% are left-footed. But when it comes to hands, the left hand dominates only 10%.
Why is this happening? Why are lefties in the minority?
In the old days, left-handedness was considered a disadvantage, and it was eradicated in every possible way even at school age. Oddly enough, the negative connotations of the word "left" have survived to this day.
The word "left" is derived from the Anglo-Saxon "lyft" meaning "weak." And its antonym in Latin sounds like "dexter" - "skillful, favorable".
So what influences which hand is leading? From an evolutionary perspective, dominating one hand makes sense. For example, chimpanzees prefer to perform certain tasks with only their left or only their right hands.
The word "left" comes from the Anglo-Saxon "lyft" meaning "weak"
Consider, for example, termite hunting. Choosing a suitable stick, chimpanzees stick it into a termite mound and, thanks to the sense of touch, receive a lot of information about its depth and width, as well as about the presence of termites in it.
Then they carefully take out a stick covered with termites, which have firmly gripped their jaws into a foreign object that has penetrated into their nest.
They have no idea that they are about to become dinner for a hungry chimpanzee. By performing the same tasks with a specific hand, chimpanzees become more agile and get more food.
But when primatologists studied the behavior of chimpanzees in their natural habitat, they found that among them there are much more left-handers: 50% of them performed the same task with their right hand, and 50% with their left.
So at what point in our evolutionary history did the 10 to 1 ratio appear?
Scientists were able to draw important conclusions by studying the teeth of Neanderthals. As it turned out, the Neanderthals were smart, but slightly awkward.
Holding a knife in a dominant hand, our ancestors cut off large chunks of meat, holding it with their teeth. From time to time they scratched their teeth with a knife.
On their incisors, clear marks were found, by which one can determine which hand was the meat, and which was the knife.
An interesting fact is that by comparing the number of left-handers and right-handers among Neanderthals, the researchers found that their ratio is 1 in 10, like in modern humans.
We know that left- and right-handedness is genetically determined. Nevertheless, geneticists are still trying to figure out which parts of DNA affect this.
Left-handed people have different principles of the functional organization of the brain.
It is estimated that up to 40 genes may play a role in determining the dominant hand.
To date, the answer to the questions about what determines our left- or right-handedness and why the left-handed minority has not yet been found.
But does left-handedness have any impact on a person's life, apart from annoyance with scissors, zippers, and other things designed for right-handed people?
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 in left-handed people the brain may be arranged a little differently.
Psychologist Chris McManus works at University College London and is the author of Right Hand, Left Hand.
“Left-handed people have different principles of functional organization of the brain,” he explains. "Personally, I think that lefties are more talented, but at the same time they can suffer from various disorders."
“Because of the differences in brain function, left-handers may have skills that other people do not have,” he is convinced.
However, not everyone agrees with this opinion. Dorothy Bishop is professor of developmental neuropsychology at the University of Oxford and has a personal interest in this matter.
“I'm left-handed, and I've always wondered why I was different from other people,” she says.
Many of the identified links between disorders and left-handedness are the result of selective reporting
“In recent years, I have heard many claims that left-handedness is associated with disorders such as dyslexia and autism. On the other hand, she was credited with positive aspects, claiming that among architects and musicians there are more left-handers."
However, after carefully analyzing the available data, Bishop questioned these findings. According to her, the identified links were the result of the selective presentation of information.
So, for example, scientists who study human creativity are wondering whether they depend on which hand is leading.
Having found confirmation of their hypothesis, they pay attention only to it, ignoring cases when such a connection is absent.
Bishop acknowledges that among people with rare conditions, including Down syndrome, epilepsy and cerebral palsy, the ratio of left-handers to right-handers is 50:50, not 1:10.
However, she believes that in these cases, left-handedness may be the effect, not the cause.
“Left-handedness in itself does not create any problems,” she explains. “It just might be a symptom of a disease. However, for most people it does not play any role in matters of intellectual cognitive development."
The controversy continues, and we still have a lot to learn about the left-handed brain.
Part of the problem is that behavioral neuroscientists only use right-handed MRI scans to minimize differences between patients.
At the same time, left-handers are invited to participate only in specialized studies on left-handedness.
Now I am seven months pregnant, and I am pleased to know that my baby has already decided who she will be - left-handed or right-handed (although I still do not know what she chose).
I know this because Peter Hepper of Queens University in Belfast has done an amazing study of how a baby moves in the womb using ultrasound.
He found that 9 out of 10 embryos had their right thumb inserted into their mouth, which is in line with the general statistics.
After meeting the same subjects many years later, he found that those who in the womb preferred to suck the finger of their right hand, became right-handed, and those who liked the left more - left-handed.
But even if my baby already prefers the right or left hand, I will not know for sure until she picks up a pencil and starts drawing.