1. Why do people walk upright?
The ability of human ancestors to walk upright is an adaptation to life in trees. Their feet are similar to palms, just like orangutans or gibbons. They can walk upright by holding branches with these feet. This not only saves energy than quadruped walking, but also frees up hands to pick fruits or swing around branches.
The fact that our ancestors left the forest is actually a very helpless story. About/kloc-0.0 million years ago, Africa was torn apart by some geological activities, which is today's Great Rift Valley. The western part of the Rift Valley is still a lush forest, so the ancient apes there have never left the forest, and their descendants have evolved into chimpanzees and bonobos today, while the eastern part of the Rift Valley has become arid and barren, and the forest has disappeared. The unlucky people who stay here are our ancestors.
Nowadays, most apes are vegetarians, but when our ancestors left the forest, they naturally lost inexhaustible fruits and young leaves, so eating meat became a necessary option. The earliest human ancestors who came to the grassland had the same brain capacity as chimpanzees today, which was not enough to make powerful tools to deal with prey. The ancestor's trick to hunting was one word, run.
Our ancestors will probably keep jogging after their prey and force them to stop. As long as cattle and sheep keep moving for a few hours, they will lose their mobility completely because of overheating, and even fall to the ground and die.
Second, why humans have almost no body hair, and how to explain hair, beard, armpit hair and so on.
As for why human beings have almost no body hair, there is actually nothing to argue about in academic circles. The exposed skin with well-developed sweat glands is only for heat dissipation.
If hair can also be interpreted as a blanket that blocks the sun, what should hair in other places block?
On the one hand, eyebrows can prevent sweat and rain from flowing into the eyes. On the other hand, eyebrows are also an indispensable communication tool for human beings. With a shrewd eye, everything speaks for itself.
Axillary hair is definitely not necessary for survival, because children have no axillary hair. As a secondary sexual characteristic, the existence of armpit hair is bound to be related to both sexes. Primates usually attract each other through their buttocks when they are in estrus. There are both visual factors, such as a red monkey's ass, and on the other hand, there are also odor factors. Monkeys can judge whether the opposite sex is thinking of themselves by smelling their butts.
However, when humans walk upright, it is not so convenient to smell their buttocks. Some scientists believe that human armpits have replaced buttocks and become the source of pheromones. Sweat glands in armpits can produce a very strong smell, and loose armpit hair is like a sponge pad, which can keep this smell and make it last longer. Hugging may be a ritual to smell each other's armpits.
Explaining beards is a hassle, not only to explain why men have beards, but also to explain why women don't have beards. Women are not genes without beards. As long as enough androgen is injected, everyone can grow a beard, which is the physiological guarantee of male charm. Androgen can stimulate muscle growth and make people stronger and more aggressive, which means more hunting gains in primitive society.
Then, a beard is probably a sign of a man's strength. For women, a man with a beard is a guarantee of enough meat. For a man, an aggressive beard can also make his competitors retreat and avoid unnecessary life-and-death struggle. On the other hand, a woman's chin is smooth, which shows that she lacks androgen and that she is a gentle mother.
Third, does the bigger the head mean smarter?
The size of the brain is not necessarily proportional to intelligence. Einstein, a famous wise man, expressed his willingness to donate his head after death. As a result, his wish came true. His head was cut into more than 200 pieces and studied by scientists all over the world. The final result is that, morphologically, Einstein's head is smaller than others'. In addition, a large number of studies have shown that intelligence has nothing to do with brain type. The intellectual difference between people comes more from education and growth environment, and no one is born smarter. What's more, wisdom is a multi-dimensional thing, and it is difficult for you to directly compare Cao Xueqin and Bill Gates who is smarter.
In short, the connection between intelligence and brain size is scientifically untenable. It is also difficult for us to find a convincing ultimate cause of head enlargement. From the perspective of pure evolution, the big head has brought a lot of trouble to people. In order to solve these troubles, human beings even changed their own marriage system.
4. Why did human society choose monogamous marriage system?
This can be explained from many angles. From the perspective of social and economic development, due to the increase of wealth, people will choose their own children to inherit, which requires strict monogamy; Judging from the ratio of men to women, this fair heterosexual distribution system is helpful to reduce competition and social contradictions. The author of this book, starting from the problems faced by mankind, believes that monogamy is caused by reproductive dilemma.
All the characteristics of human beings have left a mark on fertility. The large head and huge pelvis required to walk upright make childbirth a terrible challenge. Moreover, in order to give birth to big-headed babies, all babies have become premature babies, and their skulls have not healed at birth, which makes their heads soft and can pass through the narrow birth canal. If human children develop well like other mammals, the pregnancy cycle will exceed 2 1 month.
In the primitive state, a woman gives birth to a child in about three years on average. In addition to the difficulty of childbirth, women have to endure a long lactation period. This also means that it is almost impossible for a woman to support herself in the most fertile decade. In the meantime, a man must be tied to provide food and take care of herself. This man is usually the father of those children. Therefore, monogamy is undoubtedly the best choice, which can not only make women get stable care, but also make men basically ensure that they have offspring.
Therefore, monogamy is the inevitable result of gender game and same-sex competition, which in turn promotes the evolution of both sexes to cater to this order. In addition, women have evolved a quite clever strategy, that is, recessive ovulation.
Humans can participate in sex at almost any time. This strategy is extremely rare in primates. Although we firmly believe that this strategy is brilliant, we have not fully understood the mystery.
Scientists have two diametrically opposite theories about this. One of them is called the good father theory. Because they don't know when women ovulate, men can only wait for women for a long time, and they dare not go out to have sex casually. Such a man will naturally become a good father and raise this woman and their children wholeheartedly.
The opposite is the bad father theory. This theory assumes that in primitive society, both men and women are playboys, and men are more ferocious and may kill any children who don't belong to them. Recessive ovulation means that every man who has had sex with himself may be the father of this child, thus protecting his offspring. In addition, recessive ovulation can also make women provide more sexual resources, thus avoiding tribal men from competing for fleeting mating opportunities.
These two theories are based on some assumptions about primitive society, so they may never be known, but the theory of good father is very reasonable for the order of our modern society. In modern society, recessive ovulation has become an important guarantee of today's marriage system.