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.
Handedness and brain functionEdit
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. 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.
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 case in point. 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. 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 mankindEdit
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. For protection, catching prey and for making tools, handedness is critical.
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). 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.
- Annett, Marian 2013. Handedness and brain asymmetry: the right shift theory. London: Taylor Francis. ISBN 9780415648264
- 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. ISBN 0-12-597300-4
- Banich, Marie 1997. Neuropsychology: the neural bases of mental function.
- 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.
- Note that Arabic is written from left to right, and Japanese may also be written vertically.
- Hopkins W.D. 1996. Chimp-handedness revisited 55 years since Finch (1941). Psychological Bulletin Review 3, 449-457.
- 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 ArchaeologicalResearch.
- Zeigler, H. Phillip & Hans-Joachim Bischof eds. 1993. Vision, brain, and behavior in birds. Cambridge, MA: MIT Press, p239.
- “Southpaws” by Nora Schultz: New Scientist 1 May 2010 pages 36-39.