The Y chromosome is one of the two sex chromosomes (X and Y). Only men carry the Y chromosome. The Y chromosome is male specific, passing from father to son. It is responsible for many male characteristics.
The path of evolution is usually so quirky and complex that scientists shy away from making predictions. But the future of the Y chromosome seems clear. Graves points out that, on average, three to six genes have disappeared from the Y every million years since the chromosome emerged. At that rate, the Y has only 10 million years left. It's an old chromosome, at death's door.
The death of the Y doesn't mean the death of men. Men need only look to the mole vole for comfort. Burrowing through the soil of western Asia are two species of these rodents (Ellobius tancrei and E. lutescens) that have lost all the genes from their Y chromosome--in fact, they no longer have a Y chromosome at all. In one of these species, both males and females have been left with just the unpaired X; in the other, both sexes have two X's. No one knows how mole voles ended up being the first mammals to cross over into the Y-free future. But along the way, they must have evolved new genes--on other chromosomes--that are responsible for making males. One of those genes took over the job of SRY, and the chromosome on which it resides is probably on its way to becoming the new Y.
If our species manages to survive for another 10 million years, our descendants will go on making men even after their Y chromosome vanishes. But the change may not be smooth. Graves speculates that several new systems for determining sex could emerge within the global human population. People conceived under one system might be genetically incompatible with those conceived under others. As a result, the human species could fragment into separate populations and, ultimately, separate species. Which of them will prefer football and which the ant nest, we'll have to wait and see.
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