Theories On Handedness

Environmental theories on left handedness

Birth stress

Left-handed people cringe at this theory, because its basic premise is that left-handedness is due to brain damage during the birth process. Unfortunately, some statistics do back this theory up.

Difficult or stressful births happen far more commonly among babies who grow up to be left-handed or ambidextrous. Birth stress is also associated with a number of birth defects and complications, including cerebral palsy and autism.

But there are objections; you can breathe easy now:

Throughout history and throughout the world, the level of medicine and technology to assist with childbirth has improved. In spite of that, the proportion of left-handed people has not decreased. (In a sense, it has increased because more people see left-handedness as the benign trait it is.)

It does not explain why humans are right-handed by default, with only birth stress making them left-handed. It could, however, explain left-handedness in combination with some of the other theories presented here.

Parental pressure

This theory explains right-handed dominance by claiming that since the parents who raised us are mostly right-handed, we came to be mostly right-handed and so on.

Objections:

It does not explain how right-handed dominance started in the first place.
The handedness of children is more closely related to their biological parents than to adoptive parents.
It does not explain why left-handedness has persisted for so long.

Social stigma and repression of left-handedness

Throughout history being left-handed was considered as negative - the Latin word sinister meant "left". Hence the many negative connotations associated with the word "left-handed": clumsy, awkward, unlucky, insincere, sinister, malicious, and so on. There have been, however, many famous left-handed people, and the associated right brain hemisphere that is said to be more active in left-handed people, has been found in some circumstances to be associated with genius and is correlated with artistic and visual skill.

Until very recently in Taiwan, left-handed people were strongly encouraged to switch to being right-handed (or at least, switch to writing with the right hand). It is more difficult to write legible Chinese characters with the left hand than it is to write Latin letters. Remember that "easy" and "difficult" depend on the person using those terms, so your writing may be neater. Because it is supposedly easier to write when moving your hand towards its side of the body, it is easier to write the Roman alphabet with your right hand than with your left. Conversly, Arabic and Hebrew, which go from right to left, would be easier to write with the left hand. Again, "easier" and "harder" are subjective.

It is possible that sun worship relates to the association of the left with evil. People in the northern hemisphere, looking south, would see the sun rise on their left, move rightwards across the sky, and set on their right. In the southern hemisphere the opposite happens. Among cultures from the southern hemisphere, right-handedness is still dominant. No study on left-side connotations from those cultures has been done.

However, since most sun-worshipping cultures see the setting sun as it dying or vanishing, the right side would indicate the negative associations associated with a setting sun. This is the opposite trend from that.

Left-sidedness

In humans

Studies show that left-handedness does not necessarily correspond with "left-sidedness" (using your left foot to kick with, for example). The same thing holds with "eyedness."