The evolutionary cause for which there are left-handed and right-handed people

17/03/2018

The evolutionary cause for which there are left-handed and right-handed people
Lateness dates back to prehistory and it is believed that it confers advantages in cooperative groups
PEDRO GARGANTILLA
Updated: 03/17/2018 02: 00h7
What did Aristotle, Alexander the Great, Leonardo da Vinci, Napoleon and Marilyn Monroe have in common? All of them were within ten percent of the world population that has left laterality, that is, they were left-handed.
Human beings are asymmetric by nature, our heart is on the left side of the chest, our right lung is different from the left, the liver is in the right abdomen ... Our brain and, therefore, our behavior would not be different , most of us use preferably one hand in front of the other.
Evolutionary advantages of laterality
The laterality, or the dominance of one side of the body over the other, has implications in many areas of our life. For example, at the sport level, being left-handed offers competitive advantages in some sports, such as baseball, tennis, fencing or boxing.
When comparing laterality in chimpanzees, it is observed that when they walk on all fours there are no preferences, but that they tend to perform more actions with one hand at the moment they walk upright. From this it follows that having a dominant hand must have represented some kind of evolutionary advantage when we adopted the standing position.
On the other hand, scientists argue that the more social an animal is, where cooperation is highly valued, the greater the tendency to use one side of the body. This is because a society is more efficient the greater the degree of cooperation. This has translated, in human beings, in which most of us are right-90%. So, ten percent left-handed represents the fact that we are not totally cooperative?
The evolutionary reason that underlies laterality is, at least in theory, that by sharing the same dominant hand, we could lend us different gadgets, such as tools. All this is fine, but why the right hand instead of the left hand?
There were lefties in prehistory
Left laterality is "poorly viewed" and has a pejorative connotation, at least linguistically. For example, in English the expression "to be left" also means "to be clumsy"; in Italian «sinistra» irremediably refers us to «sinister» and in French, «gauche» comes from the Latin verb which means to err as well as vagabond.
We have plenty of evidence of people skilled in prehistory. The cave paintings show human faces with the gaze directed towards the left side, which is the artistic tendency of the right-handers when drawing facial profiles. These paintings also show us human figures holding utensils and weapons in their right hands.
We also have reliable evidence that there were "left-handed prehistoric painters". On the walls of the Cueva del Castillo (Cantabria) there are printed forty-five hands "in negative". When our ancestors of the Upper Paleolithic carried them out, they had to put one hand on the rock and cover it with a crushed reddish mineral. If the artist was right-handed, the hand that supported was the left, and conversely, if he was left-handed, the negative hand he left to posterity was the right hand, with the thumb to the left.
Well, of the forty-five hands, six of them have the thumb to the left, which represents 13% of the sample, a figure quite similar to the percentage of left-handers that there are today. Proportion that remains in the cave of Las Manos (Argentina), made with the same technique as in Cantabrian paintings.
M. Jara
Pedro Gargantilla is an internist at the Hospital of El Escorial (Madrid) and author of several books of disclosure.