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¡¡¡¡Olivia and Brett are busy wrapping presents for their father¡¯s birthday.

¡¡¡¡Brett: Are you done with those scissors yet?

¡¡¡¡Olivia: If they weren¡¯t made for right-handed people, I¡¯d have finished with them ages ago.

¡¡¡¡Brett: Oh well, that¡¯s what you get for being a southpaw.1

¡¡¡¡Olivia: Blame it on the genes, I guess.

¡¡¡¡Brett: You mean handedness is hereditary? Is there a single gene that can determine that?

¡¡¡¡Olivia: Actually, nobody really knows. It probably is genetic, but so far no one has been able to ascertain2 its pattern of inheritance.

¡¡¡¡Brett: I wonder why the ratio of right-handed people to left-handed people isn¡¯t more balanced. I mean, over ninety percent of people are righties.

¡¡¡¡Olivia: I read an interesting theory about that. It talked about the evolutionary origins of preferential3 right-handedness in humans.

¡¡¡¡Brett: And what was the conclusion?

¡¡¡¡Olivia: Well, human---and maybe even prehuman---mothers have always tended to hold their babies on the left side.

¡¡¡¡Brett: That probably has something to do with soothing a baby with the sound of the mother¡¯s heartbeat, right?

¡¡¡¡Olivia: Exactly. And so naturally, the hand not holding the child---the right hand---would be more dexterous.4

¡¡¡¡Brett: But that doesn¡¯t explain why men would be right-handed.

¡¡¡¡Olivia: And it certainly doesn¡¯t explain why you ask so many questions.

¡¡¡¡Brett: OK, OK. Let¡¯s get back to the task at hand. ---by Sonya Roy