Left-Handed Evolution and Prehistory
Scientists disagree as to when, exactly, handedness began to play a factor in human activities, with some tracing hand and foot preferences to before the time of primates and others to the time of the cavemen.[1,2] While it is certain that many primates, including chimpanzees and prosimians, show slight hand preferences, many other less related animals, including the fiddler crab, also prefer one side over the other.[1] This leads scientists to believe that handedness may have at least been making an appearance at this time, but how strongly and whether it was present in an even more distant ancestor are still open-ended questions.
Perhaps more important to tracing the evolution of handedness is the question of why one hand began to be favored over the other. At the moment, the most prominent theory is that handedness developed as a result of some of the first, most basic tools: rocks thrown at small game for hunting.[1] Researchers theorize that having a hand that was especially coordinated and strong would be an evolutionary advantage, and that the gene for such a skilled hand happened to be the right hand.[1]
Taking this idea several steps further, it has been noted that this comparatively complex mechanism requires a fair amount of brain power. Because of this, an emphasis of the left hemisphere of the brain over the right (called lateralization), would begin to develop. With language centers usually located in the left side of the brain, the promotion of the left hemisphere over the right would play an important role in the development of human communication as well, thus boosting the evolutionary fitness of right handed individuals even further.[1]
Setting up a timeline for such a shift is difficult and by necessity rather vague. After all, signs of handedness are few, as are remains from prehistoric times. Using conjecture, bone structures, and prehistoric tools, scientists estimate that some sort of handedness began to show approximately 2-3 million years ago,[2] with a slow tipping towards the right hand approximately 2-1.5 million years ago (44% left handed compared to 56% right).[1] By 30,000 years ago, the percentage of sinistrals was down to 23%,[1] and dipped further until, in modern times, it has evened out at approximately 10%.
While this theory does explain the evolutionary advantage of right handedness, it does not explain why left handedness declined so slowly, and in fact why it has remained at all. In order to remain in a gene pool, left handedness must bring some sort of advantage as well.[2]
To answer this question, scientists turn once again to the organization of the brain. As has been stated earlier, most people-- and especially most right handed people-- have their language centers on the left hemisphere of the brain, which is to some extent allowed to dominate the right. People with a pair of genes both coding for right handedness (see the Southpaw Science link) have this structure, along with several others, rigidly programmed into their brain with very little variation.[1,2] People with two genes that allow for left-handedness, on the other hand, have perhaps too much fluidity in how their brain is organized, and the left hemisphere of the brain does not have to be dominant.[1,2] It is theorized that this added randomness has the potential to seriously affect a left-handed person's mental performance, gifting some with high levels of mental abilities, while inhibiting others. The optimal gene pair, according to this theory, would be one coding for the right hand, while the other allows for the left. Because the genes are thought to be co-dominant (each one at least partially expresses itself), the brain structure of these individuals would fall in between the too-stiff and the too-loose of pure righties and lefties, allowing them to have the benefits of both and promoting the survival of both genes, albeit in different amounts.[1,2]
Perhaps more important to tracing the evolution of handedness is the question of why one hand began to be favored over the other. At the moment, the most prominent theory is that handedness developed as a result of some of the first, most basic tools: rocks thrown at small game for hunting.[1] Researchers theorize that having a hand that was especially coordinated and strong would be an evolutionary advantage, and that the gene for such a skilled hand happened to be the right hand.[1]
Taking this idea several steps further, it has been noted that this comparatively complex mechanism requires a fair amount of brain power. Because of this, an emphasis of the left hemisphere of the brain over the right (called lateralization), would begin to develop. With language centers usually located in the left side of the brain, the promotion of the left hemisphere over the right would play an important role in the development of human communication as well, thus boosting the evolutionary fitness of right handed individuals even further.[1]
Setting up a timeline for such a shift is difficult and by necessity rather vague. After all, signs of handedness are few, as are remains from prehistoric times. Using conjecture, bone structures, and prehistoric tools, scientists estimate that some sort of handedness began to show approximately 2-3 million years ago,[2] with a slow tipping towards the right hand approximately 2-1.5 million years ago (44% left handed compared to 56% right).[1] By 30,000 years ago, the percentage of sinistrals was down to 23%,[1] and dipped further until, in modern times, it has evened out at approximately 10%.
While this theory does explain the evolutionary advantage of right handedness, it does not explain why left handedness declined so slowly, and in fact why it has remained at all. In order to remain in a gene pool, left handedness must bring some sort of advantage as well.[2]
To answer this question, scientists turn once again to the organization of the brain. As has been stated earlier, most people-- and especially most right handed people-- have their language centers on the left hemisphere of the brain, which is to some extent allowed to dominate the right. People with a pair of genes both coding for right handedness (see the Southpaw Science link) have this structure, along with several others, rigidly programmed into their brain with very little variation.[1,2] People with two genes that allow for left-handedness, on the other hand, have perhaps too much fluidity in how their brain is organized, and the left hemisphere of the brain does not have to be dominant.[1,2] It is theorized that this added randomness has the potential to seriously affect a left-handed person's mental performance, gifting some with high levels of mental abilities, while inhibiting others. The optimal gene pair, according to this theory, would be one coding for the right hand, while the other allows for the left. Because the genes are thought to be co-dominant (each one at least partially expresses itself), the brain structure of these individuals would fall in between the too-stiff and the too-loose of pure righties and lefties, allowing them to have the benefits of both and promoting the survival of both genes, albeit in different amounts.[1,2]
Left-Handedness: Western History
Kerr Castle, known for its left-handed stairs
Going back to the emphasis on the power of the 'right hand of the Lord' in Hebrew Scriptures and the unflattering opinions of the Ancient Greeks concerning the left in general,[1] the Western world has had a long past with the left side that is worth noting Although almost every culture has some history with the support of one hand over another, the most well documented is that of the West (to see the others, go to the Culture and Chirality page on the left sidebar).
Western culture has had a distrust for the left that dates back to the ancient times. Aristotle, in fact, stated that "The starting point is honourable, and above is more honourable than below, and front than back, and right than left."[3] Even the Greek and Roman alphabets favored the use of the right hand over the left; because of its right to left direction, a right handed person is able to pull the pen (or stylus) across the paper, allowing the hand to move naturally and the person to see what they have written as they go.[1,2] Left handed people, on the other hand, have to push the pen, obscuring what they've written and, in the case of steel nibbed pens, often catching the pen in the paper as it pushes.[1,2]
More blatant than simple inconveniences was the decree by King James I of England in 1604, listing possible signs of witchcraft as including left handedness, circling a bonfire on the left (widdershins), and having a large mole or birthmark on the left side.[1] Stereotypes of the left handed as crazy, malicious, or idiotic carried for several more centuries, and even in the 1970s, Albania simply outlawed left handedness, while countries such as Spain, Italy, and all of the countries behind the Iron Curtain (except for Czechoslovakia) required that the right hand only be used for writing in school.[1]
In some cases, left handed people actually managed to turn such prejudices to their own advantage. Julius Caesar, a left handed person according to common belief, is said to have begun the Roman greeting custom of touching right hands, perhaps a precursor of our modern handshake. Because most people are right handed, such a gesture would indicate that one was unarmed... unless, of course, one was left handed like Caesar, in which case it was a simple matter to attack with a weapon in the left hand.[1]
Equally devious were the Kerrs of Scottish lore, a clan who trained to fight left handed and then built the left handed spiral staircases, giving them an edge in battle, both because their enemies had never trained against left handed swordsmen and because any battles fought in the castles themselves would favor a left handed person rather than a right handed.[2]
Western culture has had a distrust for the left that dates back to the ancient times. Aristotle, in fact, stated that "The starting point is honourable, and above is more honourable than below, and front than back, and right than left."[3] Even the Greek and Roman alphabets favored the use of the right hand over the left; because of its right to left direction, a right handed person is able to pull the pen (or stylus) across the paper, allowing the hand to move naturally and the person to see what they have written as they go.[1,2] Left handed people, on the other hand, have to push the pen, obscuring what they've written and, in the case of steel nibbed pens, often catching the pen in the paper as it pushes.[1,2]
More blatant than simple inconveniences was the decree by King James I of England in 1604, listing possible signs of witchcraft as including left handedness, circling a bonfire on the left (widdershins), and having a large mole or birthmark on the left side.[1] Stereotypes of the left handed as crazy, malicious, or idiotic carried for several more centuries, and even in the 1970s, Albania simply outlawed left handedness, while countries such as Spain, Italy, and all of the countries behind the Iron Curtain (except for Czechoslovakia) required that the right hand only be used for writing in school.[1]
In some cases, left handed people actually managed to turn such prejudices to their own advantage. Julius Caesar, a left handed person according to common belief, is said to have begun the Roman greeting custom of touching right hands, perhaps a precursor of our modern handshake. Because most people are right handed, such a gesture would indicate that one was unarmed... unless, of course, one was left handed like Caesar, in which case it was a simple matter to attack with a weapon in the left hand.[1]
Equally devious were the Kerrs of Scottish lore, a clan who trained to fight left handed and then built the left handed spiral staircases, giving them an edge in battle, both because their enemies had never trained against left handed swordsmen and because any battles fought in the castles themselves would favor a left handed person rather than a right handed.[2]
Citations
- Roth, Melissa. The Left Stuff: How the Left-Handed Have Survived and Thrived in a Right-Handed World. New York, NY: M. Evans and Co., 2005. Print.
- McManus, I. Right Hand, Left Hand. Cambridge, MA: Harvard University Press, 2002. Print.
- Lloyd, G.E.R. "Right and Left in Greek Philosophy." Journal of Hellenic Studies. 82. (1962): 61-2. Print.
