"Human cells carry 23 pairs of chromosomes, including one pair which determine gender." Image Source: SPL via BBC.
Geneticists are debating whether the human male will become extinct between 125,000 years (5,000 generations) and 5 million years from now.
This debate is due to the exponential deterioration of the Y chromosome (which only men have), compared to the relative robustness of the X chromosome. Newly-published research states that Y chromosome deterioration will slow or stop. This presumably means that humans will not eventually evolve into unisexual organisms or simply die out. From the BBC:
Men may not become extinct after all, according to a new study.
Previous research has suggested the Y sex chromosome, which only men carry, is decaying genetically so fast that it will be extinct in five million years' time.
A gene within the chromosome is the switch which leads to testes development and the secretion of male hormones.
But a new US study in Nature suggests the genetic decay has all but ended.
Professor Jennifer Graves of Australian National University has previously suggested the Y chromosome may become extinct in as little as five million years' time, based on the rate at which genes are disappearing from the chromosome.
Genetics professor Brian Sykes predicted the demise of the Y chromosome, and of men, in as little as 100,000 years in his 2003 book Adam's Curse: A Future without Men. ... Genetic deterioration of the Y chromosome has occurred because unlike with the two X chromosomes in women, there is very little swapping of genetic material between the Y and X chromosome during reproduction. This means mutations and deletions in the Y chromosome are preserved between (male) generations."The X is fine because in females it gets to recombine with the other X but the Y never gets to recombine over almost its entire length, and shutting down that recombination has left the Y vulnerable to all these degenerative forces," said Dr Hughes, "which is why we're left with the Y we have today."
Commenting on the paper, Professor Mark Pagel, an evolutionary biologist at the University of Reading and author of Wired for Culture: Origins of the Human Social Mind, said that while there might be some squabbling in academic circles over the timings of the events, the paper told us there was a future for males in the very long term.
"It's a very nice piece of work, showing that gene loss in the male-specific region of the Y chromosome proceeds rapidly at first - exponentially in fact - but then reaches a point at which purifying selection brings this process to a halt."