Men could vanish from planet Earth scientists fear after the discovery that an endangered rat lacks the male chromosome.
The same is happening to humans as the Y chromosome has been shrinking meaning eventually it could disappear, ending the male gender.
Lead author Professor Asato Kuroiwa said: "The Y chromosomes in many mammals, including us, have been shrinking over tens of millions of years - and could eventually disappear."
The endangered spiny rat lives on the Japanese island of Amami Oshima. Only a few remain.
Kuroiwa, of Hokkaido University, said: "There is no reason to think our Y chromosome is any more robust than the spiny rat’s."
A child's gender is determined by chromosomes - known as X and Y. They carry our DNA. Males have XY while females have XX.
Fathers contribute the X or Y, and mothers an X. Inherit an X and Y and you are a boy. Get a pair of Xs and you are a girl.
An award winning geneticist claimed two decades ago our Y chromosome will eventually go.
Proffesor Jenny Graves, of La Trobe University, Melbourne, told New Scientist: "I think this latest piece of work is brilliant. The evidence is very compelling."
It is believed a mixed population of males with and without a Y was present on the island within the last two million years.
Then most individuals died off, probably as a result of rising seas, leaving only males with no Y.
Kuroiwa said: "At some point in the past, the sea level rose and the land area was much smaller."
Experiments showed the species has only managed to survive by evolving a 'proto-Y' chromosome.
Since the dawn of humanity, men have played a vital role in determining the sex of their offspring.
The Y chromosome is carried by roughly half of a man's sperm. It dictates whether a child will be male or female.
If the Y chromosome is present, a child will develop into a boy, whereas a lack of this strand of DNA will result in a girl.
Kuroiwa said: "I absolutely agree with Jenny. I also believe the Y chromosome will disappear."
Both sexes in the spiny rat now have only a single X chromosome. And this could also be lost over time.
"Since it is unstable and mutations are accumulating, I think X will eventually disappear," Kuroiwa said.
It is hoped proto-X and proto-Y chromosomes will eventually become distinct and save the animal from extinction.