Handedness

Handedness is the preference for using either the left or the right side of the body for certain things. People are described as left-handed or right-handed when they prefer to write with their left or their right hand. They may prefer the use of certain hands for certain tasks.

Most people are right-handed. Many prefer to use their right eye, right foot and right ear if forced to make a choice between the two). The reasons for this are not fully understood. 

Ambidexterity is when a person has approximately equal skill with both hands and/or both sides of the body. True ambidexterity is very rare. In some sports work is done to even up the influence of the non-dominant side. Soccer is a good example.

 Handedness and brain function 
Handedness is caused by the lateralisation of brain function.Annett, Marian 2013. Handedness and brain asymmetry: the right shift theory. London: Taylor Francis.  Lateralisation is not only found in humans: it is found in many kinds of animals.

Handedness seems to follow from the brain hemisphere division of labor. In most people the left side of the brain controls speaking, and the left cerebral hemisphere of the brain controls the right side of the body.As the motor nerve fibres move down through the lower part of the brain, they cross over to the opposite side of the body. So, the movements on each side are controlled by the opposite side of the brain. Rosenbaum, David A. 1991. Human motor control. San Diego, CA: Academic Press, p. 411.  In 90-92% of all humans, the left hemisphere is the language hemisphere. Therefore right-handedness predominates. This theory predicts that left-handed people have a reversed brain division of labor.Non-purposeful (involuntary) movements are not controlled by the cerebral cortex. They are controlled by the more ancient parts of the brain in the brain stem.

 In society 
Many societies have tried to force right-handedness onto left-handed children ("forced laterality"). The general experience is that such attempts are not entirely successful, and cause distress. Writing is a good example. A right-handed script moves towards the right, and the righthanded writer's hand reveals what has just been written, which is good feedback. When a left-handed person writes a right-handed script, their hand obscures (hides) what has just been written. That interferes with the natural visual feedback to the writer. So the way our alphabet is written, moving to the right, is better for right-handed writers. 

Always there are always more right-handed people in a population. But, all the same, the world has many important scripts which are written right to left. Some, like Arabic, Hebrew, Persian and Urdu are widespread and important. It is worth remembering that in the past most people could not write. Even in England in 1800 many men signed their marriage certificate with an X, because they were illiterate (could not write). Widespread literacy came in the 19th century. So, when writing was invented, it was a few thousand years ago, and only the priests and officials needed to use it. Almost all monuments of that time used pictures as well as words, so that the mass of people could understand them. Much that we take for granted, like spaces between words (!), was not there at the start of writing, and several oriental languages can be written top-to-bottom as well as horizontally.Gaur, Albertine 1992. A history of writing. The British Library, p52. ISBN 0-7123-0270-0

On the other hand, with a keyboard, handedness does not matter. This is why the issue of handedness is not so important now as it once was.

However, there are many tools which are usually made for right-handed people, and it may be difficult and more expensive to buy left-handed versions.

 Handedness and early mankind 
Physical anthropologists have pointed out that the human ability to throw weapons such as rocks and spears is quite notable. Chimpanzees have handedness, but their ability to throw is much less good.Hopkins W.D. 1996. Chimp-handedness revisited 55 years since Finch (1941). Psychological Bulletin Review 3, 449-457. For protection, catching prey and for making tools, handedness is critical.Steele J & Unwin N 2005. Humans, tools and handedness. In Rioux V. & Bril R (eds) Stone knapping: the necessary conditions for a uniquely human behaviour. Cambridge: McDonald Institute for Archaeological Research. Handedness may have been part of the mental make-up of Neanderthals, with asymmetric wear on their teeth as evidence.PBS Eons  This would make sense, though it brings the question: "since its reason is not obvious, then why is it so widespread?". Even Darwin asked himself "Are monkeys right-handed??".Weinshank D.J; Ozminsky S.J.; Ruhlen P & Barrett W.M. 1990. A concordance to Charles Darwin's Notebooks 18361844, p281. Cornell University Press. 595n184 is the reference on p281. In general, the answer appears to be yes.

 Other animals 
Many other animals also have handedness. For example: elephants often have preferences for whether they swing their trunks to the left or the right. Honeybees have right antennas that are more sensitive to smells. Parrots can be left- or right-footed, and some don’t mind (they are ambidextrous).Zeigler, H. Phillip & Hans-Joachim Bischof eds. 1993. Vision, brain, and behavior in birds. Cambridge, MA: MIT Press, p239. Animals as different as chickens and minnows like to look for food with one eye and look out for predators  with the other. This seems to help them do two things at once. “Southpaws” by Nora Schultz: New Scientist 1 May 2010 pages 36-39.

Related pages
 Left-handedness
 Right-handedness

References

Category:Motor skills
Category:Writing