Researchers confirmed that the Y Chromosomes crucial for male sex determination, is progressively shrinking and might disappear within millions of years. This could result in only females being born or the evolution of new sex-determining genes, potentially leading to the formation of different human species in various regions.
The sex of human and other mammal babies is determined by a male-determining gene found on the Y chromosome. However, the Y chromosome, which is crucial for male development, is degenerating and might vanish in a few million years. This raises concerns about the potential extinction of humans unless a new sex-determining gene evolves. Interestingly, some rodents have already lost their Y chromosome and have adapted, offering hope for our species’ future.
The Fading Y Chromosome
The Y chromosome, responsible for triggering male development, has significantly reduced in size over millions of years. This decline has sparked discussions in the scientific community about the future of human sex determination. A research paper published in the Proceedings of the National Academy of Sciences highlights that spiny rats have already developed a new male-determining gene, which could indicate a potential evolutionary path for humans.
A Look at Evolutionary Changes
Professor Jenny Graves, an expert in genetics, explains that the Y chromosome’s size reduction is not a new phenomenon. She points out that in the platypus, the XY chromosome pair appears as ordinary chromosomes with equal members. “This suggests the mammal X and Y were an ordinary pair of chromosomes not that long ago,” Graves noted. Over the course of 166 million years, the Y chromosome has lost between 900 and 55 active genes, a rate that could lead to the complete disappearance of the Y chromosome in approximately 11 million years.
A New Era of Sex Determination?
As the Y chromosome continues to shrink, the possibility of evolving a new sex-determining gene becomes more likely. However, Professor Graves cautions that this evolution is fraught with risks. “The evolution of a new sex-determining gene comes with risks,” she said. She highlights the potential for multiple sex-determining systems to evolve in different parts of the world, leading to the emergence of separate human species. As Professor Graves pointed out, “A ‘war’ of the sex genes could lead to the separation of new species, which is exactly what has happened with mole voles and spiny rats.”
The Future of Human Reproduction
The gradual disappearance of the Y chromosome could fundamentally change human reproduction and lead to significant evolutionary developments. While it remains uncertain how this process will unfold, the implications for the future of our species are profound. Scientists continue to investigate these possibilities, recognizing that the disappearance of the Y chromosome could either lead to the evolution of new sex-determining systems or the emergence of entirely new human species.
In humans, females have two X chromosomes, while males have one X and one Y chromosome. The Y chromosome is small, containing only about 55 genes, compared to the X chromosome’s 900 genes. Despite its size, the Y chromosome carries a crucial gene known as SRY (sex-determining region on the Y), which triggers male development in the embryo. Around 12 weeks after conception, this gene activates others that lead to the formation of the testes, which produce male hormones, ensuring the baby develops as male.
The Disappearing Y Chromosome
Most mammals share a similar X and Y chromosome system, but this comes with challenges due to the unequal dosage of X genes between males and females. Surprisingly, Australia’s platypus has sex chromosomes more akin to those of birds, suggesting that the mammalian X and Y chromosomes were once an ordinary pair of chromosomes. Over millions of years, the Y chromosome has lost most of its active genes, leading to predictions that it might disappear within 11 million years.
Rodents That Lost Their Y Chromosome
Despite the alarming possibility of the Y chromosome’s disappearance, some rodents offer a glimmer of hope. The mole voles of Eastern Europe and the spiny rats of Japan have lost their Y chromosome and the SRY gene but continue to survive. Research on the spiny rats, conducted by Hokkaido University biologist Asato Kuroiwa, revealed that most Y-linked genes had relocated to other chromosomes. However, the gene that substitutes for SRY was not initially found.
In 2022, Kuroiwa’s team identified a small duplication near the SOX9 gene on chromosome 3 in spiny rats, which may serve as a new sex-determining switch. This discovery suggests that while the Y chromosome may disappear, a new mechanism for determining sex could evolve.
