Not the ‘Right’ Way

mmg's picture

In this paper, I am going to explore the nature of handedness.  Handedness, or the preference of the use of one hand over the other for undertaking motor and other such functions, differs for different people. Being a left handed person, I have had to answer the ‘Are you lefty?’ question probably as many times as the ‘Where are you from?’ one. It is one of those ways in which I stand apart from a lot of people. Scissors, can openers, and desks are always there to remind me, if not the people. The incidence of one kind of handedness far outnumbers the other – 9 right handed people for every one left handed person in the world. In language too there is a ‘right’ way to do something, and a ‘left-handed compliment’ to give; someone is your ‘right-hand’ man, or someone else is ‘sinister’ (from the Latin sinistral – meaning the left). Left handed people are clearly the minority, and clearly the ones whose choice of handedness are ‘less socially acceptable’. Even so, there are left-handed people in the population, and they have been here for all of documented history. Nine to one. This then really brings us to lots of different questions, and ideas.

 

The human brain is arranged such that certain parts perform or are concerned with certain specific functions. One of the broadest dimensions of this is that the two hemispheres – the left and the right, have completely different functions. Brain lateralization, or the difference in the structure and function of the two hemispheres, is often seen in the whole animal as a bias towards one side to perform motor functions, for instance (handedness). From a lot of experiments (mostly with split brain patients) the left hemisphere’s dominance over language has been established. A theory put forward by Michael C. Corballis of the University of Auckland in New Zealand states that much of that the dominance of right handedness may have to do with use of gestures (which prevailed before language fully developed). If the left hemisphere of the brain is responsible for speech and thus outer communication, then it may have controlled these gestures too[1]. Contralateralism – a widely accepted theory dictates that the opposite hemisphere of the brain controls the actions of one side of the body. The left hemisphere thus controlled the right side of the body, and the right hand developed more strongly[2]. For most part of the population. If the left hemisphere controls the right side of the body in a right handed person and is also the centre for language in the brain, shouldn’t the opposite be true for a left-handed person – i.e. language controlled by the right hemisphere, in accordance with Corballis’ theory? Yet, a study in 1975 at the Montreal Neurological Institute showed that for two thirds of left-handed people language is still controlled by the left hemisphere. For the remaining one third, it is either controlled by the right hemisphere, or both sides function together, controlling different language functions. This disparity, along with the claim that handedness arose out of a need fort the brain hemisphere division of labour[3] makes us question the presence or a need of left-handedness.

 

There have been many negative attributes – physical, immunological, cultural and mental, that are associated with being left-handed. Different studies claim that left handedness is ‘a marker for decreased survival fitness’, low IQ, premature births, low birth weight, chronic epilepsy, psychiatric disorders such as manic-depression and schizophrenia. There is also a slight stigma attached to left-handedness. Norman  Geschwind discovered that left-handed people are two and a half times more likely to suffer from allergies, reading and writing handicaps, skeletal abnormalities, stuttering, and thyroid illnesses, which are collectively dubbed the Geschwind Syndrome. Given all these ‘drawbacks’ to being a left-handed person, why is it that the rate of left-handed people in the population has remained the same for more than 10,000 years? (Since the Upper Paleolithic Age, an approximate 10% with cultural variations[4]) There are so many traits associated with left-handedness that impede survival. Why the forces of natural selection did not act against left-handedness is one of the most important questions here. Shouldn’t there have been at least some reduction in the number of left handed people, if not an elimination of left-handed populations?

 

 

The answer perhaps lies in the genes. Natural selection works with heritable factors. Yet, the heritability of handedness hasn’t been established. It is not entirely dependent on a gene. Researchers have found that even with both left handed parents the probability of a child being left-handed is 26%. With one left handed parent, it is 19.5% and with two right-handed parents its 9.5%. There is no such ‘gene’ for handedness. What is heritable, however, is the degree of a person’s handedness. A parent passes on the extent to which a person is either left or right handed, more than the direction of handedness[5]. Handedness is not then, entirely genetic. Studies conducted at Queen’s University in Belfast, Ireland show that by the 15th month of pregnancy fetuses show a preference to suck for one thumb over the other. The babies tend to stick with this preference after birth too. At 15 weeks, the brain has not developed to control the body’s limbs.[6] This then leads us to wonder if this early preference sticks through one’s lifetime. If it were true, then it would lend more interest to the ‘elusive factor’ controlling handedness.

 

What really is the purpose of having left-handed people in the population? There is the notion that lefties are creative people, and that they ‘think out of the box’, yet these haven’t been sufficiently validated yet. It is just possible, that given the amount of ‘right-handed thinking’, if one may call it that, that the ‘left-handed thinking’ just appears distinct in its own right and thus ‘out of the box’, or that left-handed people have to work harder to be noticed. There are other advantages, too. Left-handed people are better at certain sports, and tend to have an advantage over opponents in sports such as boxing or fencing where the majority are used to right-handed opponents. Such traits are desirable, but do not to me seem to carry enough weight to justify the evolutionary need for left-handedness.

 

Through the animal kingdom, we see instances with preference for one side over the other too. Chickens attack more readily when a threat appears on their left. Some fish species tend to swim left when a predator attacks, whereas others tend to go right.[7]  Chimpanzees prefer to use their left hands to ‘fish’ for termites. Thus, this is a trait that presents itself through different evolutionary levels of progress. Does it persist to add to the variety of individuals in a species? An interesting idea here needs the mention of a theory which believes that left-handedness is caused by increased levels of testosterone during pregnancy. Now, elevated levels of testosterone can delay development of the left hemisphere of the fetal brain which may result in compensatory right hemisphere growth. Such “testosterone poisoning” is also believed to account for certain mathematical and spatial gifts. Higher incidents of these are seen in males than females. Geschwind and his colleague Albert Galaburda theorized this association of gift with disorder and called it the “pathology of superiority.[8]” The fact that one of the ‘causes’ for left-handedness ties with the acquisition of such superior traits presents an intriguing idea –  is left-handedness going to contribute to our evolution to some higher forms?

At present, I take left-handedness to be a joint product of genes and the environmental influences. These include postnatal influences – such as cultural preferences for one kind of handedness. The lateralization of the asymmetrical brain offers other explanations. There is a lot of generalisation associated with the left and right hemispheres of the brain. It was hard for me to sift through that information since it is hard to conclusively draw inferences regarding a certain trait or quality of the left or right side of the brain without running into contradictions to the same. Does the specificity of certain parts of the brain in terms of a function the perfect set-up or is ‘moving’ towards a more integrated brain in terms of function a better idea in the long run? Is asymmetry the ‘right’ way to go?

         


[1] Linke, Detlef B, and Sabine Kersebaum . "Left Out." Scientific American Mind Jun. - Jul. 2005: 78-84.

[2] From Mouth to Hand: Gesture, Speech, and the Evolution of Right-handedness. Michael C. Corballis in Behavioral and Brain Sciences, Vol 26, No. 2, pages 199-260; April 2003.

[3] "Left-handedness: Does it mean anything? ." Psychologist World.com . 24 Feb. 2009 <www.psychologistworld.com/influence_personality/handedness.php >.

[4] Faurie, C and Raymond, M. Handedness frequency over more than ten thousand years. Proceedings of the Royal Society of London B 271, S43-S45 (2004).

[5] Book

[6]Left out’ Scientific American Mind, Detlef B. Linke, Sabine Kersebaum, 2005
[7] Vallortigara , Giorgio , and Lesley Rogers . "Survival with an Asymmetrical Brain: Advantages and Disadvantages of Cerebral Lateralization ." Behavioral and Brain Sciences 28 (2005): 575-633. 24 Feb. 2009 <http://trixie.brynmawr.edu:9003/brynm?sid=google&auinit=G&aulast=Vallortigara&atitle=Survival+with+an+asymmetrical+brain:+Advantages+and+disadvantages+of+cerebral+lateralization&title=The+Behavioral+and+brain+sciences&volume=28&issue=04&date=2005&spage=575&issn=0140-525X>.
[8] Winner , Ellen . "Uncommon Talents: Gifted Children, Prodigies and Savants." Scientific American Mind Mar. - Apr. 1998: 32-40.

Comments

Paul Grobstein's picture

Handedness: genes, environment, and ...

"I take left-handedness to be a joint product of genes and the environmental influences"
And, perhaps, chance? In any case, you're not the only left-hander in the class. See Ilja.

Post new comment

The content of this field is kept private and will not be shown publicly.
randomness