A lecture from a life sciences class

Narrator
Listen to part of a lecture from a life sciences class.

Prof: Raise your hand if you're right-handed. Yep, that looks typical. Most of us -- about ninety percent -- are right-handed. It's been that way throughout history. In ever...In nearly every culture, right has been associated with positive qualities, while the left has been associated with negative, or even evil, ones. In Latin, left means "sinister." In ancient Japan, men could reject, er, refuse, to marry women who were left-handed. Um, in modern China, teachers try to force left-handed students to learn to write with their right hands. And, as I'm sure all lefties know, everyday items, like, can openers, uh, scissors, and uh, computer keyboards, are designed for righties. In short, left-handers have been made to feel "left" out ... [pause]. Get it? (sound of groans).

It might seem straightforward to you and I, but scientifically speaking, the basis of handedness is not well understood. Most scientists define right-handed or left-handed on the basis of a person's preferred writing hand. [Coughs] But some scientists claim it should be based on the hand that is, um, faster and more accurate in performing manual activities, like tightening a screw or, uh, tying a knot. Still others claim that ability doesn't matter; in other words, that handedness should denote only preference. Yes, question?

S1: What about people who are anti, um, ambi, uh...who use both hands?

P: You mean ambidextrous. Actually, most scientists agree that genuine ambidexterity is rare, and several of them believe it even rates its own special category as a distinct type of handedness. Uh, the reason for this is that most people can perform several functions relatively equally with either hand, which causes another scientific faction to argue that there are actually only two types of handedness - right and non-right. This group advocates measuring handedness on a continuum, from 100-percent right-handed to 100-percent left-handed. On this scale, we'd say something like, "I'm 60-percent right-handed," or "I'm eighty-two-point-five-percent right-handed" -- though how we'd determine who's more right-handed than another would open a whole new can of worms. OK, um, yes?

S2: How do people become right-handed or left-handed in the first place? Does it come from your genes?

P: Mostly, yes. Research shows that handedness is largely genetic. Er, interestingly, though, even when both parents are left-handed, the odds are no better than 50-50 that their children will be lefties. Some scientists believe there is a specific gene that determines right-handedness, but the, uh, trouble is that they can't pinpoint it. They think this gene also aids the development of speech and language comprehension. Many researchers believe that handedness is a result of something called brain lateralization, which is the, uh, concept that each hemisphere of the brain controls different bodily functions. Researchers have long been believed that a person's dominant hand is on the side opposite the brain hemisphere that controls their language specialization, so that right-handed people use the left half of their brain for processing language. But brain lateralization, is, um, not well documented, and there is evidence that seems to contradict this concept. For instance, while it's true that more than 90 percent of right-handed people do process language in their left hemisphere, recent research shows that about 40 percent of left-handed people also process language primarily in the left side of their brain. Additionally, only 10 percent of lefties rely primarily on their right brain to process language.

So, um, what can we make of this? Though genetics clearly plays a vital role in determining handedness, environment also seems to be a fac [false start] an important factor. A recent archaeological study compared a group of modern Canadians with 1,000-year-old skeletons from a British farming community. The Canadians showed right-handed dominance by a nine-to-one ratio of larger right elbows than left ones. In the ancient skeletons, however, most right and left elbows were equal. Now, this doesn't prove that the British farmers were ambidextrous, but researchers say it does suggest that handedness can be subject to societal influence. So for many, the best hypothesis at this time is that handedness results from a complex interaction of nature and nurture.