Why do women have breasts?

Compared with other mammals, human females have very unique breasts. Females of other mammals (including our primate cousins) only have bulging breasts during pregnancy and lactation. Once the lactation period is over, they will revert to "Princess Taiping" and will not have breasts again until the next pregnancy and lactation period. Only human women begin to develop breasts after puberty. Whether pregnant or breastfeeding, breasts always exist "permanently" until old age (although there are individual differences in size). Why are human breasts so "different"? This has always been a question of great interest to biologists.

1. Breast is a luxury "burden". If it is only for breastfeeding, it is enough for human women to have "temporary breasts" like other mammals during breastfeeding. It seems unnecessary to grow such breasts, because in fact, "permanent breasts" have many disadvantages. The composition of breast is mostly fat, and its growth needs to consume a lot of nutrition. In ancient times when food was scarce, it was undoubtedly a luxury to grow a pair of "permanent breasts", and precious food calories should be used for more important life activities. Ancient women shouldered the heavy responsibility of collecting wild fruits, taking care of the old and the weak, and sometimes they had to avoid the pursuit of wild animals; Hanging two "encumbrances" on their chests will increase the inconvenience of action, reduce work efficiency, and may even make them die in the stomachs of lion claws and wolves. In addition, plump hemispherical breasts are easy to block the baby's nose and mouth, leading to suffocation (the "breast" structure of other primates is very convenient for young babies to suck). Since human breasts are so "beautiful and useless", why did they evolve into this?

2, breasts transmit "sexy signals" As we all know, breasts are women's secondary sexual characteristics, they are not only breast-feeding organs, but also have an important attraction to men. "Big breasts" can make men salivate, and advertisements, magazines and film and television programs often attract men's attention with female images with full breasts. Women with smaller breasts will feel inferior, and some will even look for "breast enhancement secret recipe" to increase their charm, and even "stand up" by breast augmentation surgery. The biological significance of female sexual attraction is not only to promote sexual intercourse and fertility. Because human beings have no fixed estrus, their frequent sexual life can be used as an emotional bond, which is conducive to the formation and maintenance of a relatively long-term and stable monogamous relationship between men and women, because both parents must invest a lot of time and resources, which is very important for the upbringing of human children. Women have "permanent breasts", which can attract male spouses for a long time and let them stay and raise their children with them, instead of "leaving". Regarding the sexual attraction function of human breasts, British zoologist and human behaviorist Desmond? In his popular science masterpiece Naked Ape, DesmondMorris believes that quadruped primates (including human ancestors) use "backward style" when mating, and females attract males with bulging hips and red labia (both located at the back of their bodies) as sexual signals during estrus; When humans walk upright and have face-to-face sexual intercourse, they will transfer the organs that display sexual signals to the front of their bodies-they will evolve bulging breasts and bright red lips as simulators of buttocks and labia to attract men.

3. Why do you want to use fussy things as sexy signals? But why use "cumbersome things" as "sexy signals"? This can be used by Israeli evolutionary biologist Amoz. In 1975, Zahawi put forward "unfavorable principle" or "HandicapPrinciple" to explain it. By showing their disadvantages to other creatures (especially heterosexual individuals) and showing off their excellent genes-the male peacock shows off his bulky big tail, in fact, he is bragging to the female peacock: "Look, I can afford such an expensive price, and I have spent a lot of extra energy to grow a luxurious big tail, which shows that my nutritional conditions are excellent, my body is extremely healthy and there are no parasites. In addition, I can move freely with such heavy things and avoid being hunted by natural enemies. All this shows that I am gifted and my genes are great, which is really your first choice for mate selection. " The permanent breast of human women is also a display of unfavorable conditions, which is essentially a "curve" to show off women's good nutritional conditions and health status to men, and ultimately it is the embodiment of having excellent genes.

4. How did ancient women evolve "constant breasts"? The existing primate species have no "constant milk" except human beings, and human beings evolved from the ancestors of all primates, and the ancestors did not have "constant milk", so the process of human beings having "constant milk" can be described as "out of nothing". For a long enough period, humans once had only "temporary breasts" like other mammals, which only bulged during pregnancy and lactation. As we all know, women can't get pregnant again during pregnancy and lactation. Therefore, if a woman's chest bulges, it is equivalent to telling a man: "I can't be pregnant with your child now, and mating with me will only waste your time and sperm." Males also avoid mating with such females. From this, it is easy to infer that ancient men once had a completely opposite "taste" for breasts with men today. They only like Princess Taiping, who may be pregnant, but they have no "sexual interest" in bulging breasts and are more resistant. Because if men actually prefer to have sex with women with bulging breasts, they will not be able to leave their offspring and their genes will be eliminated.

Therefore, this raises a question worthy of consideration: after the first batch of women with "permanent breasts" appeared due to genetic variation, how did a small part of them magically make men's "taste" of breasts change 180 degrees, become willing to have sex with them, and finally completely eliminate the women with "temporary breasts" who are absolutely dominant in evolution, thus making today's earth. Because we can't go back to the distant past in a time spaceship to see the evolutionary events at that time, and the breasts can't form fossils for research, this is probably a mystery forever.

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