The End of Men? Y Chromosome Facing Extinction: Study

The sex of human and mammal offspring is determined by a male-determining gene on the Y chromosome. However, this vital chromosome is gradually degenerating and could potentially vanish in a few million years, posing a significant threat to our species’ survival unless a new sex-determining gene emerges.

A promising development has already been observed in two rodent species that have lost their Y chromosome yet continue to thrive. According to a 2022 study published in the Proceedings of the National Academy of Sciences, the spiny rat has evolved a new male-determining gene, providing hope for the future of humanity.

In humans, females have two X chromosomes, while males carry one X and one Y chromosome. Although the Y chromosome is much smaller, containing only about 55 genes compared to the X chromosome’s 900, it plays a crucial role in male sex determination by initiating the development of testes in embryos.

Approximately 12 weeks after conception, the SRY (sex-determining region Y) gene on the Y chromosome triggers a genetic pathway that leads to male reproductive organ formation. This process involves the activation of another key gene, SOX9, which is essential for male development in vertebrates.

Over the past 166 million years since the evolutionary split between humans and platypuses, the Y chromosome has significantly declined, losing a substantial number of active genes. If this trend continues, scientists predict that the Y chromosome could disappear within the next 11 million years, raising concerns about the future of human reproduction.

Interestingly, two rodent species—the mole voles of Eastern Europe and the spiny rats of Japan—have already lost their Y chromosome and continue to survive. In these species, the X chromosome is present in both males and females, but the Y chromosome and the SRY gene are absent.

Research led by Asato Kuroiwa from Hokkaido University revealed that in spiny rats, most Y chromosome genes had relocated to other chromosomes. However, the SRY gene was missing, and a small duplication near the SOX9 gene on chromosome 3 in males seemed to take over its function. This discovery suggests that spiny rats have developed a new mechanism for male sex determination, offering valuable insights into the potential evolution of human sex chromosomes.

What This Means for Humanity

The potential disappearance of the Y chromosome raises critical questions about the future of human reproduction. Unlike some reptiles that can reproduce asexually, mammals, including humans, require sperm, making the presence of males essential for species survival.

The evolution of a new sex-determining gene, as seen in spiny rats, provides hope but also presents challenges. If different regions evolve distinct sex-determination systems, it could lead to the emergence of new human species, each with unique sex chromosomes.

In the distant future, visitors to Earth might not encounter humans as we know them today but rather several different human species, each separated by their own sex-determination mechanisms.