• Leah Hess

Exploring the Y Chromosome Extinction Theory: Are Men Going Extinct?

Updated: Aug 16, 2021


Recently, the claim that “men are going extinct” has been circulating on social media platforms such as Twitter and TikTok. Proponents cite that this is due to the eventual disappearance of the Y chromosome, which is the sex chromosome responsible for male development in mammals. So just how much truth is there to this theory? Will the Y chromosome eventually disappear? If it does, does that mean the extinction of biological males?


In eutherian mammals (mammals that have a placenta and give birth to live young), the Y chromosome first evolved at the same time as the X chromosome, about 200-300 million years ago. In humans, a pair of X and Y chromosomes make up our sex chromosomes, with an XX pair resulting in female sexual development and an XY pair resulting in male sexual development. Hence, the Y chromosome is often referred to as the male chromosome. However, besides triggering male development through a gene called the SRY gene (the “male-determining gene”) and promoting sperm synthesis, the Y chromosome isn’t critically functional.


In fact, many of the important functions of male development are actually carried out by the X chromosome, including brain and testicular development. Furthermore, the X chromosome contains about 900 genes while the Y chromosome contains only about 55 genes. The lack of functional DNA sequences contained in the Y chromosome is partially due to its degeneration over the course of its existence. It is estimated that the Y chromosome originally contained 1500 genes and has gradually been reduced due to a phenomenon called recombination inhibition. In short, this means that the Y chromosome preserves its sex-determining qualities by failing to recombine (the sharing and swapping DNA that aids in eliminating damaging mutations) with the unmatching X chromosome. In turn, this weakens the Y chromosome and makes it particularly vulnerable to gene deletion. This degradation is where the Y chromosome extinction theory has its roots. If gene deletion continues at the same rate, about 4.6 genes per million years, the Y chromosome will completely lose function within the next 10 million years.


Other mammals have already experienced this. The Amami spiny rat evolved naturally to have one X chromosome, as opposed to two X’s or an X and a Y. Experiments have also been done on mice to mimic this effect. A 2017 study published in Science Advances went on to investigate the mechanism by which this is able to occur, finding that the Amami spiny rat (and likely other rodents) have the ability to reversibly differentiate between female somatic cells (all body cells besides germline cells) to male germline cells (cells involved in passing on genetic information). In other words, even without the Y chromosome, male cells can be produced from female cells and allow for the continuation of the male species.


As can be seen in the case of the mammals described above, the disappearance of the Y chromosome does not necessitate the extinction of men. Both male and female offspring are still necessary for reproduction via the fertilization of an egg by a sperm. This is because the important male-determining genes of the Y chromosome (similar to the SRY gene) simply moved to the X chromosome. Now, males are produced without the need for a Y chromosome.


Therefore, whether or not homo sapiens retain the Y chromosome is luckily not an issue that needs to be addressed within our lifetime. Even if this disappearance were to happen tomorrow, it would likely not affect life, as men would still be around and function the same for reproductive purposes. Regardless, it is an interesting look into just how complex and adaptable the genome is and provides interesting implications for research in reproductive health and evolutionary biology.

 

Speaking Plainly:

  • The Y chromosome is the male determining chromosome and contains the SRY gene, which leads to some aspects of male development.

  • The Y chromosome has been degrading over the course of its 300 million year existence due to its inability to undergo recombination with the X chromosome.

  • If this continues, it is possible that the human Y chromosome could disappear in the next 10 million years, as has happened in certain rodent species.

  • The disappearance of the Y chromosome likely means unnoticeable gene migration and adaptation, not differences in male phenotypes or the extinction of men altogether.