The Y chromosome was formed about 150 million years ago. However, it may soon be facing extinction, wiping out the male species with it.
Homo sapiens first appeared on Earth about 2-300,000 years ago, which is actually pretty recent in comparison to the age of the planet. Since then, we have evolved constantly, adapting to the needs of survival, and have become the creatures we are today. We are the most advanced and developed beings on the planet, with all our technology and thinking and reasoning capacity. However, is our reign coming to an end? More specifically, is the male species dying?
First, let’s try to understand a little of our basic genetics before we get into the interesting part.
Chromosomes that have the same genes at the same location and are usually similar in size and shape are called homologous chromosomes. In each pair of homologous chromosomes, one is derived from each parent. These also have the ability to exchange genetic material with each other, thereby leading to variation.
The exchange of genetic material between 2 homologous chromosomes is called recombination. Recombination is an important process, even from an evolutionary point of view. It helps chromosomes combat mutational damage by being able to shuffle genetic material. It is important to keep in mind though, that genetic material can only be exchanged among homologous chromosomes. This is mainly due to the fact that these chromosomes will have genes for the same functions, although they may have different alleles.
Humans have autosomes and sex chromosomes, but our sex chromosomes evolved from autosomes themselves, about 150 million years ago. They developed from a pair of homologous autosomes to form the X and Y chromosomes, which now determine our sex. X is the female chromosome, while Y is the male chromosome.
However, evolution has proven that females are like the fall-back system in embryonic development. Unless otherwise indicated, the fetus will be a female. The indication for it to be a male comes in the form of a gene on the Y chromosome known as the SRY gene. This gene acts like a master switch that causes the development of the male gonads (testes) and stops the formation of the female parts (ovaries). This gene also controls the expression of a number of genes, thus regulating their activity.
Degeneration of the Y chromosome
The ultimate sign of masculinity, the factor that gives life to males – the Y chromosome – is now in a big mess.
The SRY gene conferred the ability to produce males, but also isolated the Y chromosomes from the other chromosomes. According to one estimate, the Y chromosome started off with about 1438 genes, but over the course of time since its formation, it has lost about 1393 of them, leaving it with only 45 genes.
Since the X and Y chromosomes were homologous chromosomes, the exchange of genetic matter took place between them. However, it’s not hard to imagine how this proved to be a bad idea. Imagine swapping your belongings randomly with a person of the opposite gender. Some items that are unisex will result in no problems and may not even be noticed. However, gender-specific items, if exchanged, will be rather inconvenient. Similarly, the sex chromosomes ended up losing genes that were essential for the development of that particular gender. Conversely, they also received genes that proved to be useless, or even harmful.
Therefore, to avoid such an inconvenience, all the genes essential for the development of a male were concentrated in certain regions of the Y chromosome. Recombination was then suppressed in these regions. This rendered 95% of the chromosome unable to undergo recombination, leaving just the 5% – its tips- to be able to exchange genetic material. These regions are called PAR – Pseudoautosomal regions. They are so called because it is only these regions that can undergo recombination like autosomes do.
The section of the Y chromosome that cannot exchange its genetic material is thus passed on from generation to generation as it is, making it extremely prone to mutation. Any harmful change in the genes in this region has very little chance of being corrected and is always passed on. Beneficial genes surrounded by harmful genes tend to get eliminated completely. Similarly, some harmful genes are able to hitchhike, or stay on the chromosome due to being surrounded by beneficial genes.
Mutations over the years, therefore, caused the Y chromosome to lose most of its genes, leaving it with only a few, a bare minimum of genes.
The reason why the X chromosome doesn’t suffer the same fate is because it can exchange genetic matter freely with another X chromosome. While this doesn’t entirely block the harmful effects of mutation, it surely manages to balance it out. Due to the possibility of variation, the X chromosome isn’t losing its genes like its Y counterpart.
We have already seen how and why an X chromosome has more genes than the Y chromosome. Does this therefore imply that women, who have two X chromosomes, will be in better shape than men, who have just a single X chromosome?
Nature is quite efficient in its functioning, and fortunately found a way to correct this imbalance. Women silence most of the genes on one of their X chromosomes in order to maintain a balance between them and males. This is known as X-inactivation. So much sacrifice!
This is also why men are more prone to certain diseases. Due to having a single X chromosome, even if they have a faulty gene, they have no other option than to use it. Women, on the other hand, do have an option.
End of Homo sapiens
According to current estimates, the Y chromosome will lose all its genes in about 5 million years. While this seems like a long way off on an individual scale, it could potentially spell the end of humanity in a very short time when we look at the bigger picture. In fact, some studies claim that currently, about 7% of the global male population is infertile. However, let’s not leave on such a bad note. It’s also important to understand some of our potential options for survival.
Let’s start with the fact that the male population will soon come to an end. While this is the general belief, recent studies have also pointed out certain facts that say otherwise. According to some studies, the Y chromosome has lost just one gene in the last 25 million years, and no gene in the last 9 million years. This leads some scientists to believe that the Y chromosome is no longer losing genes. They believe that the genes left on the chromosome are not just lucky. Instead, they are absolutely essential to the survival of the male species. These researchers believe that the Y chromosome is now stable, and will no longer undergo degeneration.
The next theory is that if the Y chromosome keeps deteriorating, it can shift the essential genes to its other chromosomes, perhaps even the X chromosome. This has been observed in certain organisms who have completely done away with the Y chromosome. They have managed to salvage the essential genes, including the SRY gene, and attach it to another chromosome. Alternatively, in some organisms, gender is decided by environmental factors other than sex chromosomes. This is another slightly encouraging possibility.
The last factor, which is still purely theoretical, acknowledges the bleakest option – the extinction of the human male. While there are still some technicalities to be taken care of, it may be possible in the future for females to reproduce with other females. While this sounds like an abomination, it may be essential for the survival of the species. Women can give birth to women, much like how daughters are born. There is no hand of the Y chromosome in the formation of a girl, and with the way science is advancing, who knows… that may be our final option
No matter how bleak this sounds, there is no way for sure to know what will happen. However, being credited as the smartest beings on the planet, perhaps we could gain an upper hand in this race against time. Knowledge of our seemingly inevitable end will almost certainly spur us to develop contingency plans…. after all, we probably have millions of years to figure it out. Only time will tell. Until then, I’m going to revel in the fact that I’m alive while Harry Styles and Tom Hiddleston exist!