Sex Linkage of Intelligence: The X-Factor

Sex Linkage of Intelligence: The X-Factor

Sex Linkage of Intelligence: The X-Factor

Sex Linkage of Intelligence: The X-Factor


The author presents a theory that major genes controlling the growth of human intelligence, both left- and right-brain attributes, are on the X-chromosome. The more significant of the implications of such X-linkage include: BL Males tend to be more variable in intelligence. BL Partial or total reversions to the aboriginal level of intelligence can account for virtually all cases of non-specific mental subnormality. BL Since the X-linked genes control a pattern of growth, boys are more variable in the age of readiness for the skills required for progress in school. BL Being on the X-chromosome, these genes, favorable or unfavorable, are not passed on from father to son, although they are passed on from father to daughter. In effect, earlier studies have come up with estimates of the heritability of intelligence that are too low.


A hundred thousand or so years ago when human beings first learned to put ideas into words, they also started trying to find the answers to a lot of questions. At first those questions related to the events in their own lives. "Why are there so few berries where there used to be lots of them?" "Where are the animals when I want to kill them for food?" "Where does the sun go at night?" "Why did my favorite mate die?"

To answer these questions, they made up theories. The natural forces at work were beyond their understanding, but they could see that people could cause things to happen and so they attributed that same power to plants, animals, and even inanimate objects. So they decided that the berries had become angry because someone had done something wrong in their presence; the animals had decided to go on a trip elsewhere to spite them; the sun, like a burrowing animal, had gone under the ground. When it came to personal misfortunes, perhaps those happened because an enemy caused them to. That is, when a favorite mate died, it may have been because of the spell cast by an envious neighbor. If too many bad things happened, it might be best to do away with that neighbor.

That kind of thinking still exists in the world. In fact, at least until recently, the bushmen of Australia felt that they were perfectly justified in doing away with a neighbor if they were satisfied in their own minds that the neighbor was the cause of their problems. And not too long ago, in our own part of the world, the "witches" of Salem were tortured and killed in the belief that they were the cause of problems in the community.

However, even in a very primitive society, the idea of blaming personal enemies for misfortunes was counterproductive. If one killed one's neighbor, on the assumption that he (or she) was the cause of one's problems, the . . .

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