Humans Could Become Extinct Unless Men Develop a New Sex Gene

The fate of the Y chromosome, responsible for determining male sex, has been the subject of much debate among geneticists. This tiny chromosome, which contains only a fraction of the genes found on the X chromosome, is shrinking. As it loses more genetic material over time, some experts worry that humanity could face extinction—unless a new sex-determining gene emerges to replace it.

The Y Chromosome’s Grim Fate

The Y chromosome, though crucial in determining male sex, has been decaying for millions of years. Originally, it was as large as the X chromosome, but over time it has lost 97% of its ancestral genes.¹ According to geneticist Jennifer Graves, the sex gene overall once contained 1,669 genes, but now only has about 55. The process of degeneration is a result of mutations and a lack of genetic recombination, which helps most chromosomes shed harmful mutations.

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Why Is It Shrinking?

The Y chromosome’s inability to recombine with the X chromosome has been the root of its decline. Recombination is a process that creates genetic diversity and helps chromosomes eliminate harmful mutations. However, since the sex gene cannot recombine with its X counterpart (except at the tips), it accumulates mutations until many of its genes become useless. Moreover, genetic “inversions” in the Y chromosome’s structure—where parts of it are flipped—have contributed to its degeneration. These inversions reduced the Y’s ability to undergo recombination, speeding up its gene loss.

The Importance of the SRY Gene

Despite its dwindling size, the sex gene still holds one critical function: it contains the SRY gene, which kick-starts male development by triggering the formation of testes in embryos. This gene serves as an “on-switch” for male traits. However, without the Y chromosome, the fate of male reproduction could be at risk, leaving humanity to potentially face extinction.

Could Mankind Go Extinct?

The big question on everyone’s mind: will the disappearance of the Y chromosome spell the end of men—and humanity? Graves’ research suggests that, if the Y chromosome continues to shrink at its current rate, it could disappear in as little as 4.5 million years. While this might seem far off, it raises questions about how the human race will adapt. In the absence of a Y chromosome, it’s possible that the human species could evolve a new sex-determining gene, as has occurred in other animals, such as certain species of rats and voles. These animals lost their Y chromosomes but still developed males and females through alternative genetic mechanisms.

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Other Species Have Survived Without Y Chromosomes

The case of the Amami spiny rat offers hope that even without a Y chromosome, reproduction can continue. These rats lost their Y chromosome about 2 million years ago, yet they still have males and females. How? A duplication near the SOX9 gene on chromosome 3 in these rats mimics the role of the SRY gene, triggering male development.² This shows that species can survive without the Y chromosome if they develop a new system for determining sex.

Can Humans Evolve a New Sex Gene?

If the Y chromosome disappears, could humans follow the path of the spiny rat and develop a new sex-determining gene? Possibly. Evolutionary biologists suggest that another chromosome, or even a new region of the genome, could take over the role of the SRY gene, allowing males to continue to exist. However, this process of adaptation may be risky, leading to complications in reproduction. Graves warns that the evolution of multiple sex-determining systems in different human populations could lead to the development of new human species, each separated by its unique method of determining sex.

The Role of Genetic Recombination in Slowing Decay

Not all experts agree that the sex gene’s fate is sealed. Some researchers, like Jennifer Hughes, argue that the Y chromosome has already proven its ability to “outsmart” genetic decay. Although the Y chromosome cannot recombine with the X, it can undergo a form of “self-repair” through gene conversion, which helps fix mutations using backup copies of its genes. This suggests that the Y chromosome may not be on a one-way track to extinction and could stabilize its gene content over time.

A New Era for the Y Chromosome?

So, should we be worried? While the Y chromosome is shrinking, it’s not gone yet—and may not disappear as quickly as some fear. Even if it does, the examples of species like the spiny rat show that humans could adapt to this loss by developing new genetic systems to determine sex. However, this process isn’t without risks. Multiple sex-determining systems could lead to the creation of new human species, complicating reproduction and potentially leading to unforeseen consequences for the human race. In conclusion, while the Y chromosome’s future may seem bleak, humanity is resilient. As Jennifer Graves aptly states, “Even if the Y chromosome does disappear, humans may evolve a new sex-determining gene, ensuring that males and females continue to exist”. For now, we can only wait and see how evolution unfolds.

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