Most friends who like to watch the evolutionary history of man know that our ancestor Homo sapiens was a romantic species. After they had sex with the ancient Neanderthals, they left some "time bombs" in our bodies, such as depression, type II diabetes, smoking addiction, etc., which really drags the modern age. The hind legs of Homo sapiens.
However, Homo sapiens owes more than these. In addition to Neanderthals, they have also been ashamed of other ancient races, and they have also had some influence on us modern people.
In 2008, in Denisova Cave in the Altai Mountains of Siberia, archaeologists discovered the following mysterious objects:
What is this? Is it pine nuts? tooth? None, but...
A girl's phalanx fragment.
Yes, in this period of Homo sapiens observation room, we are approaching Denisovan (Denisovan).
Who are they?
After the researchers discovered this precious phalanx fragment, they also discovered fossils including a phalanx, a tooth and some ornaments.
Using existing DNA to sequence it. Speculated conclusion: this piece of phalanx The owner is a 5-7 year old girl.
DNA evidence shows that this girl does not belong to any known ancient human species, so she was named Denisovan according to the place of discovery.
Dani Sowa Hole
Scientists after comparing gene sequence differences We infer that this race parted ways with our Homo ancestors and Neanderthals about a million years ago.
Denisovans rely on two feet to walk, but the body structure and Homo sapiens and Neanderthals have The difference. They have a sisterhood relationship with Neanderthals, so they look similar.
Restoration of Neanderthals
In 2012, researchers completed the sequencing of the Denisovan genome and found:
Some Denisovan genes are still retained in the modern human genome. In a sense, they are still alive in us.
In some Australasia today (including Australia, New Zealand and the neighboring Pacific Islands), especially those from Papua New Guinea, about 5% of their DNA comes from Denisovans. We ofThe ancestors of Homo sapiens had done shameful things with Denisovans 50,000 years ago, or even earlier.
Papua New Guineans
So the researchers concluded that Homo sapiens have had stories of applauding love with Denisovans in at least two places, including eastern Asia and beyond.Southeastern Indonesia, or Papua New Guinea.
Modern Homo sapiens With the Denisovan gene in the body, it can also be regarded as a gift from some ancestors: the Tibetan people on the Qinghai-Tibet Plateau have a very strong adaptability to the plateau (with a special hemoglobin level regulation mechanism), and may have to feelThanks for this gene.
In addition, the genes of Denisovans and Neanderthals also helped modern Homo sapiens have a stronger immune system to a certain extent.
Unfortunately, the hybridization of Homo sapiens ancestors left us not only advantages, but also buried some bugs:
Researchers suspect that the hybridization of Homo sapiens ancestors may lead to Male offspring have decreased fertility.
Has modern male fertility declined?
The reason for this suspicion is that after the researchers analyzed the ancient human* genes, they noticed that both the Denisovan and Neandertal genes are on the X chromosome of modern humans. Its content is significantly lower than that on autosomes, even less than 1/3 of autosomes.
Is this swollen?
Therefore, one possible situation is: when Homo sapiens has a hybrid romance, gender The matching is not balanced. The main reason is the combination of female Homo ancestors and male ancient human ancestors, so mixed boys cannot inherit the X chromosome of Homo sapiens father, so it is inherited from generation to generation, and the ancient human gene content of the X chromosome is low. /p>
Then why grandpa Homo sapiens is not willingWant to have sex with Denisovan grandma? Is it because the female Denisovan is not good-looking?
Or, is it because the male ancient human ancestors snatched the grandma of Homo sapiens and forcibly... But if it was looted in such a large amount, wouldn't it be discovered and beaten by the grandfather of Homo sapiens?
Actually, The researcher has another explanation. They believe that the low content of X chromosomes in ancient humans is due to the decline in the offspring of hybrid males. After some ancient humans (such as Denisovans) genes entered the genomes of the early Homo sapiens ancestors, the originally harmless genes may become genes that have an adverse effect on male fertility and are generally concentrated in the X chromosomes of hybrid male offspring.
In the process of natural selection, this harmful gene is gradually eliminated, resulting in the ancient human gene content on the X chromosome being less than that of the autosome.
However, regardless of whether the ancestral romance has affected male fertility, men should still be concerned about their reproductive health.
Because in the last forty years, the sperm concentration and number of western men (mainly including North America, Europe, Australia and New Zealand) have dropped sharply to half, and the chromosomes are not as good as before.one tenth.
A review published in "The Human Reproduction Update" in 2017, studied 7,518 articles published from 1981 to 2013, collected and analyzed 185 studies Of 42935 male sperm data. The analysis results show that in the past 40 years (from 1973 to 2011), the sperm concentration of a single ejaculation in Western men decreased by an average of 1.4% per year, an overall decrease of 52.4%; the total sperm count decreased by an average of 1.6% annually, an overall decrease 59.3%.
The main culprits are pesticides, plastic products, obesity, tobacco, social pressure and so on.
Neither will I tell you that the Y chromosomeshort.
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 in 4.5 million years . The males of Eastern European mole and Japanese voles in nature have lost their Y chromosomes during the evolution process.
According to research conducted by various institutions, the frequency of sexual life of modern young people (mainly those born in the 90s) has indeed decreased:
"Workplace Human Life Report" From Netease Chunfeng
A study of nearly 27,000 people in the United States shows that compared with their peers in the 1960s and 1980s, fewer adults aged 20-24 now have sexual partners, and more Many young people choose Buddhist abstinence (research published in Archives of Sexual Behaviour).
(It cannot be ruled out that young people’s understanding of papa papa has changed, leading to deviations in the survey results.)
What I want to tell you is the "good news". Don’t tell him, it’s:
Anyway, all men are "transgender". It doesn’t matter if there is a Y chromosome.
Actually, what I mean is that it is the SRY gene on the Y chromosome that really determines the sex, not the Y chromosome itself.
The expression of the SRY gene is like a switch, which is responsible for starting the formation of the testis and the subsequent development of male organs. Its target is SOX9. In the XY chromosome, if the expression of SOX9 is enhanced, the helper cells will go to form a male organ. If SOX9 lies in place and neither increases nor weakens, then the helper cells will continue to develop into femalesSex organs, it's useless to have Y chromosomes.
Moreover, with the advancement of technology, offspring can be born without sperm.
In 2015, the Li Jinsong team of the Shanghai Academy of Biological Sciences of the Chinese Academy of Sciences successfully used the eggs of two mice to reproduce healthy offspring.
Not to mention that as early as 20 years ago, the cloned sheep Dolly was born by three mothers alone.
Hearing this, you breathed a sigh of relief: Finally, you don’t have to worry about your fertility decline?