A leading researcher has claimed that the day is not far off when humans will become extinct.
Professor Jennifer Graves, a leading researcher in human sex chromosomes, claims the male Y chromosome was dying and could run out within the next five million years.
However, the expert said, men could follow the path of a type of rodent that manages to reproduce despite not having the vital genes that make up the Y chromosome.
While at the annual outreach public lecture at the Royal College of Surgeons in Ireland, Graves told medical students that a second species of human beings could even be born in the future, reports The Scotsman.
"You need a Y chromosome to be male," said Prof Graves, from Australia.
"Three hundred million years ago, the Y chromosome had about 1,400 genes on it, and now it's only got 45 left, so, at this rate, we're going to run out of genes on the Y chromosome in about five million years. The Y chromosome is dying and the big question is what happens then," she added.
The male Y chromosome has a gene - SRY.
SRY switches on the development of testes and pumps out male hormones that determine maleness.
She said it was not known what would happen once the Y chromosome disappeared.
"Humans can't become parthenogenetic, like some lizards, because several vital genes must come from the male," she said.
"But the good news is certain rodent species - the mole voles of Eastern Europe and the country rats of Japan - have no Y chromosome and no SRY gene.
"Yet there are still plenty of healthy male mole voles and country rats running around. Some other gene must have taken over the job and we'd like to know what that gene is," she added.