February 1, 2023

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Why do we prefer to use the right hand?

raise the but not As if you were in school. Which hand did you choose? For nine out of ten, that must have been right: left-handed people did not “extinct”, despite the fact that until a few years ago they were often corrected, but they were nailed to 10% of the population, in Everywhere and in any ethnic group. No other primate has such a marked preference for the right hand, so much so that it has been suggested that right-handedness is almost as defining to humans as the opposite thumb: so one wonders why we chose the right. It is the result of an evolutionary advantage, as it may have given us brain more effective? Or did it happen over thousands of years for cultural reasons, for example because the idea that the left hand is the hand of the “devil” gradually took root?

Homo habilis was right-handed. Meanwhile, it seems certain that the Whig’s preference appeared early on date manThe first fossils that indicate that it dates back to 1.8 million years ago. There are not enough complete skeletons from the period to verify whether our ancestors were left-handed or left-handed by evaluating differences in the shape or size of the bones of the extremities; So David Fryer from the University of Kansas (USA) and Luca Pondioli from the National Museum of Prehistory in Rome focused on the teeth, studying the direction of scratches obtained by primitive men by trying to cut shreds from a piece of stone with a stone blade. Clamp the meat between their teeth, to deduce which hand is holding the instrument.

Decoding some analysis Homo habilis Found in the Olduvai Gorge on the African Serengeti Plateau, which is called the “cradle of humanity” precisely because the oldest human remains come from here, archaeologists have discovered that even then, the right hand was mostly used to grasp tools. Similar probes for a much larger number of fossils Neanderthals They have been found in various regions of Spain, France, Switzerland and Iraq by researchers at University College London: Even those hominids who lived very recently (from about 100,000 to 35,000 years ago) were rarely left-handed.

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Moreover, it is possible that the choice of the right hand goes back to the time when we came down from the trees, about eight or ten million years ago: according to the cognitive psychologist Stephanie Praccini of the University (Scotland), according to which the asymmetry in the use of hands probably appeared when We assumed the status quo.

«Experiments with chimpanzees also indicate this: when they stand on four legs, they do not show a preference for one side or the other, if they are forced to stand on two, the preference for one side is clearly shown.Praccini says. The “descending from the trees” theory has not been proven, but there is enough agreement that at least 1.8 million years ago we became mostly left-handed. However, the reasons why this happens remain a mystery, even if the most reliable hypothesis calls into question what is called lateralization of the brain.

brain question. «The two cerebral hemispheres They are not identical either in microstructure or morphology, nor above all in functions: different activities are carried out by different regions of the cerebral hemispheres, often by only one, sometimes in such a way as to involve both”explains Luca Tomasi, Professor of Biological Psychology and Physiological Psychology at the University of Chieti. «Coordination is ensured by neural cross connections: in practice, the movements of the right hand depend on the motor areas of the left hemisphere, and vice versa. Therefore, manual skills and cerebral lateral organization are two essential aspects and are necessarily related to each other».

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According to the so-called Homo loquens hypothesis of evolutionary biologist William Fitch of the University of Vienna, when we became bipeds, we differentiate functions in different aspects of the brain to improve their efficiency; So the left hemisphere specialized in language, one of the most important functions of our species, and this brought with it as a side effect the manual preference for the right, which this hemisphere commands.

Young Muppets, an important minority. Finding the evidence is not easy, given that neuropsychological tests must have been done on our ancestors; In addition, language does not always appeal to the left hemisphere, and there is not always concordance in the part of the brain that is activated for speaking and moving the preferred hand. As Tomasi points out, “In 5% of right-handed people, language activates the right hemisphere, and in 70% of left-handed people, the left hand controlling the right hand is activated. Language and dexterity are often, but not always, controlled by the left side of the brain: thus these two variances of function are not necessarily related. Furthermore, there are hypotheses about the opposite sign, for which verbal language could have evolved from hand gesture.».

It is difficult to understand whether the language of eggs or the chicken’s use of right comes first, but the need to develop skills will constitute a stable balance reached in the course of evolution.

Tomasi adds:This relationship is likely to last for a long time, because it appears to be the optimal relationship between individuals interacting synergistically, when they have to share tools, and antagonistic, when they struggle. In our earlier physical competitions they were more frequent and left-handed people had an advantage in it, as we still see in competitive fighting or contact sports like tennis or football, because of the sudden effect that makes their movements unpredictable; With the massive spread of social communication and shared culture, the need for physical coordination prevailed, for the use of all the same tools».

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So it was biology and society that became the main reason for becoming right-handed, and then it cannot be denied that culture also counted, even only in recent centuries: the left has always been considered an unclean hand (it is no coincidence that Eve grabbed the right sin apple with the left) And so until very recently left-handed people were corrected to write with sticks. We will therefore remain the only species with a clear right-handed tendency: even the animal’s brain is not symmetrical in its functions, Tomasi explains, “There are preferences for using one aspect at the individual and population level, but in this case the second percentages are often less pronounced than in humans».

and animals? We will therefore find left-handed or right-handed cats, but the cat as a species does not have a marked inclination like the human; The same is true of primates, chimpanzees for example are only 60-70% right-handed. The exception that proves the rule? Parrots, especially those belonging to the family Cacatuidae, large parrots characterized by the “tuft” on the head: in many species there is a preference for the feet with which to grasp objects up to 85% or even 100%. However, unlike us, he is left-handed.