Are humans still evolving? Four generations of mice living together give us inspiration

I always see people saying that in developed countries, no matter they are born with disabilities or IQ problems, they will live well, and most of them will leave their own offspring. Then won't the natural selection of the survival of the fittest stop? Have humans stopped evolving?

Let me start with something that is clearly in the process of evolution: 1. appendix; 2. coccyx; 3. wisdom tooth degeneration; 4. Y chromosome. I won't explain the first three, but the fourth one is quite special and interesting, so let's talk about it today.

01 Y chromosome

Anyone who has studied biology knows that the Y chromosome is the male sex-determining chromosome, so there must be male-determining genes on the Y chromosome. There are two genes on the Y chromosome that are most critical to sex determination: Sry and Eif2s3y. Sry is responsible for the development of the fetus into sex, and Eif2s3y is related to spermatogenesis. However, the truth of the matter is actually like this.

In essence, the Sry gene is just an awakening gene that is used to awaken the expression of Sox9 on the autosomes. This gene is the sex-determining gene.

Likewise, a homolog of the Eif2s3y gene exists on chromosome X, called the Eif2s3x gene.

In other words, the two core sex-determining genes on the Y chromosome are not that critical and irreplaceable...so, you know...

02 Y chromosome and X chromosome

The Y chromosome is homologous to the X chromosome, but later due to the duplication of some functions, the Y chromosome became shorter and shorter in evolution. Originally there were 1669 common genes, but now the Y chromosome is only 1/3 of the length of the X chromosome, and the genes are even fewer, only 50 genes.

In fact, the loss of Y chromosomes in mammals is a very obvious phenomenon, because these genes can be attracted by other chromosomes, and then this chromosome is useless. At present, the Y chromosomes of the following mammals have been lost:

1. Two species of Japanese spiny rats;

2. Two species of field mole vole.

The Y chromosome genes of these species have been transferred to other chromosomes. Of course, there are also objections, such as the following article (http://www.nature.com/news/reprieve-for-men-y-chromosome-is-not-vanishing-1.15103#b1), the author believes that the Y chromosome contains core components related to cell function, which is evolution's favorite content, so the Y chromosome is not necessarily lost, and the Y chromosome itself has not changed for a long time, so the Y chromosome will not be lost.

Anyway, a few great bricks are flying around, and this thing will depend on the future. However, no matter what, the Y chromosome is too short and has too few genes, so it is quite easy to lose it.

03 If the Y chromosome is gone, will it be a country of women?

But, does the absence of Y chromosomes mean a land of women? Not necessarily...

Previously, Science published an article that completely knocked out the Y chromosome gene of mice, but the mice were still able to become fathers, which shows that our poor Y chromosomes are really going to be kicked out. The process of this experiment is roughly like this.

We mentioned above that there are two key genes on the Y chromosome, Sry and Eif2s3y. Sry is responsible for the development of the fetus into males, and Eif2s3y is related to spermatogenesis. So, this interesting Y chromosome replacement is shown in the figure below. You can see that the sex-determining gene on the Y chromosome has been replaced.

The result is that they live well without the Y chromosome. The following pictures show three male mice that do not contain any Y chromosome genes. Note that these are males.

The mice on the left and right are 2 years and 1 month old, while the mouse in the middle is 1 year and 10 months old.

Moreover, they can reproduce offspring!

The picture above shows four generations of male mice without any Y chromosome genes.

The white mouse on the left is a male mouse without Y chromosome gene, which was originally obtained through cross breeding. It was successfully bred with the help of ROSI technology. The mouse in the middle of the upper row (F1 ROSI) is its son, which also has no Y chromosome gene at all. F2 ROSI and F3 ROSI are the grandchildren and great-grandchildren of the white mouse respectively.

How about this research, is it cool enough?

04 Smoking shortens the Y chromosome

By the way, smoking will shorten the Y chromosome and thus shorten men’s life. This is not what I said, it is what science said.

Compared with non-smokers, men who smoke for a long time have shorter Y chromosomes or even disappear. The direct result is that the risk of various cancers increases by 2 to 4 times; they even lose their fertility. The possible reason is that smoking accelerates the loss of Y chromosomes.

The reason mentioned by the author is that smoking may increase the probability of mutation of genes and pathways involved in cell mitosis regulation, which in turn leads to the truncation of Y chromosomes. Normal cells carry this truncation and continue to divide and proliferate, eventually leading to this phenomenon.

By the way, smoking is hereditary and directly affects the next generation. Smoking directly affects the epigenetic changes in sperm and is passed on to the next generation.

So, smokers, take it easy...

Finally, a few words. Remember that Darwin's theory of evolution is only a part of evolution. Natural selection is just a screening method, not the core process. To put it bluntly, natural selection is just a description of the current natural world, not the essential cause. To exaggerate a little, evolution does not need natural selection at all. Similarly, evolution itself is directionless.

But it doesn’t mean there is no choice. If you can’t breathe oxygen or receive sunlight, you will still be chosen…