The Y chromosome is the fastest-changing part of the human genome and undergoes rapid evolution through constant renewal, new research suggests.
The first comparison of the male chromosomes of humans and chimpanzees have revealed vast differences between the two, far more than scientists expected.
The Y chromosome, responsible for creating males, contains about two per cent of the DNA in a human cell. Men carry one X chromosome and one Y; women have two Xs.
The new research suggests that human male chromosomes have evolved more quickly than the rest of the genome over the last six million years since humans and chimpanzees split from a common ancestor.
Researchers at the Whitehead Institute for Biomedical Research at MIT in Cambridge, Mass., sequenced the chimpanzee Y chromosome for the research. It is only the second Y chromosome to be sequenced, after the human's.
The scientists expected to find that the two chromosomes would be very similar. The widely held scientific theory on the Y chromosome is that it is a stagnant structure that evolves very slowly.
Instead they found that the chimp Y chromosome has lost up to half of the human Y chromosome genes.
"The region of the Y that is evolving the fastest is the part that plays a role in sperm production," said Jennifer Hughes, a postdoctoral researcher at the Whitehead Institute, in a statement.
"The rest of the Y is evolving more like the rest of the genome, only a little bit faster," said Hughes.
The researchers said their finding, published this week in the journal Nature, doesn't mean that men are evolving faster than women, though.
Instead, they likened the Y chromosome to a house that's under constant renovation.
"People are living in the house, but there's always some room that's being demolished and reconstructed, and this is not the norm for the genome as a whole," said David Page, director of the Whitehead Institute.
The scientists said the rapid divergence of the Y chromosome from the common ancestor of humans and chimpanzees may be due to differences in mating behaviour.
In chimpanzees, multiple males may mate with a female one after the other, resulting in intense competition among the sperm to fertilize the egg.
If a chimp produces more sperm, it's more likely that its sperm will fertilize the egg and pass its genes on to the next generation.