Most friends who like to read the history of human evolution know that our ancestor Homo sapiens was a popular species. After they snapped out of the mixed race with the ancient Neanderthals, they left some "time bombs" in our bodies, such as depression, type II diabetes, smoking addiction, etc., which really dragged the hind legs of modern Homo sapiens.
However, homo sapiens owes more than that. In addition to the Neanderthals, they were also ashamed of other ancient races, and they also had some influence on our modern people.
In 2008, archaeologists found the following mysterious items inside the Denisova Cave in the Altai Mountains of Siberia:
What is this? Pine nuts? tooth? Neither, but...
Fragments of a girl's phalanges.
That's right, in this period of the Homo sapiens Observation Room, we are close to the Denisovan.
Who are they?
After the researchers found the precious phalangeal fragment, they also found fossils including a phalange, a tooth and some ornaments.
Sequence it using existing DNA. Speculation leads to the conclusion that the owner of this phalangeal bone is a little girl of 5-7 years old.
DNA evidence suggests that the little girl does not belong to any known ancient human species and was named Denisovan according to the place where she was found.
Denisova Cave
After comparing the differences in gene sequences, scientists deduced that this race had parted ways with our Homo sapiens ancestors and Neanderthals about a million years ago.
Denisovans walk on two feet, but their body structure is different from that of Homo sapiens and Neanderthals. They were sisters with neanderthals and therefore looked similar.
Restored neanderthal statue
In 2012, researchers completed sequencing the denisovan genome and found:
Some denisovan genes are also preserved in the genome of modern humans. In a sense, they are still alive in us.
About 5% of some of today's Australasia (including Australia, New Zealand, and the neighboring Pacific Islands), especially from Papua New Guinea, derives about 5% of the DNA from Denisovans. Our Homo sapiens ancestors did shameful things with the Denisovans 50,000 years ago, or even earlier.
Papua New Guineans
So the researchers concluded that Homo sapiens had had stories of love applause with Denisovans in at least two places, including in eastern Asia and further afield in southeastern Indonesia, or Papua New Guinea.
Modern Homo sapiens have Denisovan genes in their bodies, and they can also be regarded as some ancestral gifts: the Tibetan population on the Qinghai-Tibet Plateau is extremely adaptable to the plateau (with a special mechanism for regulating hemoglobin levels), which may be thanks to this gene.
In addition, denisovan and Neanderthal genes have also helped modern Homo sapiens have a stronger immune system to some extent.
Unfortunately, this kind of hybridization of homo sapiens ancestors has left our descendants with more than good qualities, but also buried some bugs:
Researchers suspect that crossbreeding of Homo sapiens ancestors may have contributed to a decline in fertility in male offspring.
Has modern male fertility declined?
The reason for this suspicion is that after analyzing the paleoanthropter* gene, the researchers noticed that the amount of the Denisovan and Neanderthal genes on the modern X chromosome was significantly lower than on the autosomal body, or even less than 1/3 of the autosomal body.
Is this swelling?
One possible scenario for this is that homo sapiens have a hybrid affair with homo sapiens, and the gender mix is uneven. Mainly female Homo sapiens ancestors and male paleogenous ancestors are combined, then mixed-race boys can not inherit the X chromosome of Homo sapiens father, so generation after generation, the X chromosome in the paleohuman gene content is low.
So why wouldn't Grandpa Homo sapiens want to snap with Denisovan Grandma? Is it because the suspect Denisovan is not good-looking?
Or maybe it's because the male paleogenous ancestors snatched the Homo sapiens grandmother forcing..... But if it was such a large-scale plunder, wouldn't it be discovered by The Grandfather of Homo sapiens and then beaten violently?
In fact, the researchers have another explanation. They believe that the low ancient human content of the X chromosome is due to the decline in fertility of hybrid male offspring. After some paleo-human (e.g., Denisovan) genes entered the ancestral genomes of early Homo sapiens, otherwise innocuous genes may become genes that adversely affect male fertility and are generally concentrated in X chromosomes that cross male offspring.
In the process of natural selection, this harmful gene is gradually eliminated, resulting in a smaller amount of ancient human genes on the X chromosome than the autosomal.
However, regardless of whether the ancestral feud affected male fertility or not, men should still be concerned about their reproductive health.
Because in the last four decades, the concentration and number of sperm in Western men (mainly in North America, Europe, Australia and New Zealand) have plummeted to half of the original, and the chromosomes are less than one-tenth of what it used to be.
A 2017 review published in The Human Reproduction Update studied 7518 papers published between 1981 and 2013 and collected and analyzed 42,935 male sperm data from 185 of these studies. The results of the analysis show that over the past 40 years (from 1973 to 2011), the sperm concentration of a single ejaculation in Western men has decreased by an average of 1.4% per year and by 52.4% overall; the total sperm count has decreased by an average of 1.6% per year and by 59.3% overall.
The main culprits are pesticides, plastic products, obesity, tobacco, social pressure, and so on.
Nor will I tell you that the Y chromosome, an important gene for men, is getting shorter and shorter.
More than 16 million years ago, the X and Y chromosomes were the same length, but now the Y chromosome is only 1/3 of the X chromosome, and some researchers speculate that the Y chromosome will disappear completely after 4.5 million years. The males of the Eastern European mole and the Japanese vole in nature lost the Y chromosome in the process of evolution.
According to research by various institutions, the frequency of sex life of modern young people (mainly post-90s) has indeed declined:
"Workplace Human Life Report" comes from NetEase Spring Wind
A U.S. study of nearly 27,000 people showed that fewer adults aged 20-24 today have sexual partners than their peers in the 1960s and 1980s, and more young people choose Buddhist abstinence (the study was published in the journal Archives of Sexual Behaviour).
(It cannot be ruled out that the young people's understanding of papa has changed, resulting in a deviation in the results of the survey.) ）
What I want to tell you is a "good news" that I don't tell him most people, and that is:
All men are "transgender" anyway. There is no big deal about having the Y chromosome.
I mean, it's the SRY gene on the Y chromosome that really determines gender, not the Y chromosome itself.
The expression of the SRY gene is like a switch, responsible for initiating the formation of the testicles and later the development of male organs. Its object of action is SOX9. In the XY chromosome, if SOX9 is enhanced, the helper cells go to form male organs. If SOX9 is lying in place, neither strengthening nor weakening, the helper cells will continue to develop into female organs, and having the Y chromosome is useless.
Moreover, with the advancement of science and technology, no sperm can give birth to offspring.
In 2015, Li Jinsong's team from the Shanghai Academy of Biological Sciences of the Chinese Academy of Sciences successfully used the eggs of two mice to produce healthy offspring.
Not to mention that as early as 20 years ago, Dolly the cloned sheep was already born simply by three mothers.
Are you relieved to hear this: finally don't worry about your fertility declining?