Warning sign: Men are going to become extinct, and women will rule the earth.

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Although the average height of men worldwide has increased by about 15 centimeters over the past 200 years,
the length of the Y chromosome, which determines male sex, has been steadily shortening.

More than 16 million years ago, the X and Y chromosomes shared a common origin, each containing 1669 genes, but now the Y chromosome is only one-third the length of the X chromosome.
Will the Y chromosome disappear in the future?
Will this mean the extinction of men from the planet?
The increasingly shorter Y chromosome and X and Y chromosomes have high specificity, possessing unique genes.

American geneticist and Nobel laureate Herman Miller pointed out in 1914 that
sex chromosomes originate from autosomes, because almost all genes on the Y chromosome can be found as alleles on the X chromosome. The X and Y chromosomes together determine the sex of humans and other mammals.
For example, in humans, if both parents give you an X chromosome, your offspring will exhibit female characteristics; if your parents give you a Y and an X chromosome respectively, your offspring will exhibit male characteristics.

However, mismatches can occur, such as XXX, XXY, or XYY. These mismatches caused by sex chromosomes can not only lead to sex confusion but also serious diseases.

Besides causing gender confusion due to mismatch, the disappearance of the Y chromosome could also lead to the extinction of males or male animals. Its negative impact would be no less than detonating an "atomic bomb" within a male animal population. When your parents give you a Y and an X chromosome respectively, your offspring will exhibit male characteristics. As mentioned earlier, the human Y chromosome originally had thousands of genes, just like the X chromosome. However, over time, the Y chromosome has become increasingly specialized, with genes being continuously lost, and now it has fewer than 50 genes.

In fact, three mammals have already lost their Y chromosomes during evolution. Will humans follow in their footsteps?
However, some research has given men renewed confidence. Experimental results show that the Y chromosome has been relatively stable for a long period and has not been shortening as expected. A likely reason is that the genes preserved on the Y chromosome need to pair with homologous genes on the X chromosome to function, and natural selection has preserved these genes. Therefore, current predictive models regarding whether the Y chromosome will disappear in 4.5 million years may not be accurate.

Although scientists discovered the Y chromosome in 1905, the sex-determining gene SRY on the Y chromosome wasn't discovered until 85 years later, in 1990. Only then did researchers unravel the mystery of the key gene determining sex in humans or other mammals. Researchers found that if the SRY gene is missing, the testes, which determine male characteristics, will not develop.
In fact, besides SRY, other genes on the Y chromosome are not without function; their absence can cause developmental disorders in the entire mammalian population. A major sex crisis under climate change: Our planet is also home to a large number of cold-blooded animals, which once dominated the Earth for hundreds of millions of years with their vast populations and astonishing size.

Although existing cold-blooded animals are still well adapted to the ever-changing environment, their survival crisis is becoming increasingly prominent. These animals include reptiles, amphibians, and fish. Their sex is determined not only by genetic factors, but also by environmental factors, specifically temperature.
They are not strict sex enforcers; under different temperature conditions, they exhibit different sexual characteristics. With current global warming, extreme temperature conditions will lead to an increasingly severe imbalance in the sex ratio of these animal groups.

A team of researchers studied a common lizard species in central Australia—the bearded dragon—and discovered that sex reversal can occur within a single generation under extreme temperature conditions. Surprisingly, male bearded dragons with the ZZ sex chromosome were phenotypically identical to artificially induced females with the ZZ sex chromosome, and they could even mate, producing only male offspring. The W chromosome, which determines female sex, disappeared completely within a generation. If extreme temperatures continue in the future, the W chromosome of this species is likely to disappear, and the resulting sex imbalance could lead to the extinction of the species. Without males,

the entire Earth would be a "land of women." What if the Y chromosome disappeared?
For mammals, the disappearance of the Y chromosome means the extinction of male individuals and even the entire species. Are there any cases where species have survived despite the disappearance of the Y chromosome? The mole vole and two species of spiny rats in Japan are typical examples. During the evolution of the spiny rat, the Y chromosome was inadvertently lost, along with the gene that determines sex. However, the CBX2 gene on chromosome 2 in this species still plays a role in determining male sex. This news might give humanity renewed confidence.

If humanity doesn't face extinction due to sex imbalance, will other chromosomes or genes evolve to determine human sex?
Perhaps after the Y chromosome completely disappears and the SRY gene is lost, this gene, or several genes, will jointly determine human sex.
But then, will humans still be human?

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Warning sign: Men are going to become extinct, and women will rule the earth.

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