This phenomenon may disappear in a few million years, potentially leading to our extinction unless a new sex-determining gene evolves.

In humans, females have two X chromosomes, while males possess one X and one Y chromosome. The Y chromosome, though much smaller with only about 55 genes compared to the X chromosome’s 900, plays a vital role in determining male sex by triggering the development of the testis in an embryo.

At around 12 weeks after conception, the master gene on the Y chromosome, known as SRY (sex-determining region Y), activates a genetic pathway that leads to the formation of male reproductive organs. This gene works by stimulating another key gene, SOX9, which is crucial for male development across vertebrates.

Most mammals share a similar X and Y chromosome structure, but this system presents challenges due to the unequal gene dosage between males and females. Interestingly, Australia’s platypus possesses entirely different sex chromosomes, resembling those of birds, suggesting that the mammal X and Y chromosomes were once ordinary chromosomes.

Over the 166 million years since humans and platypuses diverged, the Y chromosome has lost a significant number of active genes, shrinking from 900 to just 55. If this trend continues, the Y chromosome could vanish entirely within the next 11 million years.

But there is a good news too. Two branches of rodents have already lost their Y chromosome and survived. A 2022 study published in peer review journal ‘Proceedings of the National Academy of Science’ reveals that the spiny rat has successfully evolved a new male-determining gene, offering hope for humanity’s future.