What could a future free of men look like? We could soon find out. According to recent research, the Y chromosome, the crucial factor that determines if someone is male, is starting to fail.

In fact, the Y chromosome has already heavily degenerated and could eventually disappear completely. But what will happen once it’s gone?

Will we have a new sex? Or would the male species just suddenly cease to exist? We spoke to Jenny Graves, a renowned Australian geneticist and leading expert on the Y chromosome to give us the lowdown on what's going on.

Why could the Y chromosome be on the way out?

First, we need to refresh our memory on sex chromosomes. In humans, as well as in some other mammals, females have two X chromosomes. Males on the other hand have a single X and a Y.

These pairs of chromosomes only make up roughly 4 per cent of a human’s total DNA, and determine their sex.

“Chromosomes come in pairs, but the sex pair is unusual for its difference in males and females. While females have two Xs, which is a very large chromosome, men have an X and Y,” Graves says.

“In comparison to the X, the Y is tiny. There are only 45 genes on the Y chromosome, and it is just one of these that makes you male. A few others help make sperm, but for the others, we don’t quite know why they are there. We just can’t really get rid of them. That's compared to between 900 and 1400 in the X”.

Originally, the Y chromosome was similar to the X and had over 900 genes. Now just 45 are left. Because the sex chromosomes evolved from completely normal chromosomes that were identical, having nothing to do with sex, a lot of what is left is essentially useless.

With its somewhat funky history, it might not come as a surprise that the Y chromosome is starting to crumble. But it’s not just a human problem, the same thing is happening to other animals. Fruit flies, for example, have already lost almost all of their Y chromosomes.

“The reason for this loss seems to be two-fold. One is that the Y chromosome by definition is always in a testicle, never an ovary. It turns out that the testicle is a dangerous place to be partly because there is a lot of mutation going on,” says Graves.

“For making sperm, a lot of cell divisions are needed and each cell division is a chance for mutation. This can have quite an effect on the chromosome. It’s also just not very good at fixing itself up because there is only one in the cell.”

Most chromosomes can repair damage from mutations by swapping DNA with the opposite chromosome. This is a process known as recombination. However, because the Y chromosome is inherited alone, it has no swappable partner, unlike a female’s double X chromosome setup.

What does that mean for the future of the male species?

Compared to its original state, the human Y chromosome has now lost roughly 97 per cent of its ancestral genes. The X chromosome on the other hand remains relatively untouched.

With such rapid degeneration, what does this mean for the male species? Are we on the verge of a world with no human males?

“When I say rapidly, I’m talking in the evolutionary sense. Sex chromosomes evolved in mammals roughly 180 million years ago. It has taken that long for the Y chromosome to erode to this level,” says Graves.

“It’s funny that people get so upset about the loss of the Y chromosome. My rough calculations are that we’ve got another six or seven million years until the chromosome is completely gone.”

Unless the billionaires of the world finally manage to crack immortality, it is highly unlikely any of us will be around to see even the beginnings of the Y chromosome breaking down. But what could it look like in theory?

There are some animals that are able to produce offspring from unfertilised eggs through a process known as parthenogenesis, but that’s not possible for humans.

“We have a number of genes that have to come through sperm in order to be active. These are known as genomically imprinted genes. We do need men and we do need sperm. However, there is an alternative,” says Graves.

“We could simply evolve a new sex-determining gene. That’s what we’ve already seen happen in some types of rodents, and it seems to have worked successfully.”

Two separate species of rats, mole volves in Eastern Europe and spiny rats in Japan, now completely lack a Y chromosome. They simply have evolved to do sex determination differently, moving all the important Y chromosome genes to other chromosomes.

However, while this has all worked out just fine for these rodents, there is no guarantee of how it would go in humans. Creating new sex genes is actually quite simple, the problem is what happens when you’ve got an old and new one coming in at the same time.

“This causes a battle of the sex genes," says Graves. "You might have one male-determining gene on a Y chromosome and another found elsewhere. These could develop in different parts of the world, creating a separation of the human species.”

Right now, this is all speculative. The Y chromosome is degrading, that much is clear. The future result, on the other hand, is less so. In millions of years, men could simply cease to exist. We could equally see an evolutionary change with an entirely new sex forming.

In fact, with so many humans around the world and the innate weirdness of the Y chromosome, Graves believes that somewhere there could already be a man born without a Y chromosome for the first time.

About our expert, Jenny Graves

Jenny Graves is a geneticist and professor with the La Trobe Institute for molecular science. She has published over 430 articles including 4 books on the subject of genetics. She has been a leading figure in the research of human evolution and the evolving world of the Y chromosome.

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