The long nipple is not the future, it may start the "breastfeeding function"
Release date: 2009-12-21 As the name implies, the most important feature of mammals is breastfeeding. Human beings as a member of a mammal, the reason why women have nipples is very obvious. But why do men have nipples? Not only men, but also other male mammals have nipples. In the 18th century Europe, this was a problem that was very embarrassing to natural theologians. Natural theologians believe that the structure of the organism is subtly designed by God and embodies the wisdom of God. But why does God want to have two nipples that are obviously useless in men? Disposable Underpads,Assurance Underpads,Disposable Underpads Bulk,Disposable Bed Underpads Shandong Kangshun Daily Products Co., Ltd , https://www.centurybenifit.com
When Darwin created the theory of evolution, he also pondered this question. He suspects that in mammalian ancestors, males and females are equally responsible for breastfeeding, when male breasts are also well developed. Later, for some reason (for example, the number of litters per litter was reduced), the male was no longer needed to be a "nursing mother", and the male breasts slowly degraded.
Although this speculation is imaginative, there is no basis. In the days of Darwin, people were ignorant of the mechanisms of biological inheritance. If Darwin has modern genetics, he may be able to make a more reasonable answer. We know that human genes are stored in 46 small parcels called chromosomes, half of which are given by the father and half by the mother, with 23 pairs. Of the 22 pairs, there is no difference between men and women, called autosomes. Related to gender is the 23rd pair of chromosomes, called sex chromosomes. A man's sex chromosomes are not actually paired, a large one (called the X chromosome) is a small one (called the Y chromosome). A woman has two pairs of X chromosomes.
The genes related to the nipple and breast are all on the autosome, the same for both men and women. In the third week of embryonic development, the nipple begins to appear. At this time, the embryo did not even have gonads. At week 5, the gonads appear, but at this time the gonads are neutral, and it develops into testes or ovaries, depending on whether there is a Y chromosome. There is a gene on the Y chromosome that determines testicular development. If the Y chromosome is present, the gonads will begin to develop into testes at week 7. If the Y chromosome is not present, the embryo's gonads will wait until the 13th week to develop into the ovary.
You may think that the X chromosome has something to do with the development of women. actually not. Some people have an X chromosome, which is XXY. Guess what gender they are? male. The extra X chromosome does not work. It can be seen that the Y chromosome is the chromosome that determines the gender. If there is Y, it develops into a male. Without Y, it develops into a female. So the sex chromosome is X or XXX that develops into a female. If there is no sex chromosome or only Y chromosome? These embryos can't develop because there are many important genes on the X chromosome, and you can't live without it. Unlike the Y chromosome, it is dispensable.
Shortly after the development of the embryonic gland with the Y chromosome into the testis (week 8), the testes began to produce androgens, and under the influence of androgens, the reproductive organs of the fetus gradually differentiated into males. If there are no androgen, the reproductive organs of the fetus will grow into women. Although the ovary of the female fetus also produces estrogen, it has no effect on gender differentiation. Whether the fetus is male or female, the body has estrogen from the mother.
Some people have sex chromosomes that are XY, they have testes, testes can also produce androgens, but genes encoding androgen receptors are mutated, and androgen cannot bind to androgen receptors on cells. As a result, although there are androgen in these people, androgen does not work. These people not only have external genitalia like women, but also have sex like women, and even more attractive than normal women. Because normal women have a small amount of androgen that can function, just like normal men have functions. A small amount of estrogen, and only estrogen in these people is working, of course, feminine. These people have been raised as women since childhood, and some have become female models because of their beautiful appearance and sexy body. They are often found to be men when they wait for menarche to go to the doctor. They have no female reproductive organs. The testicles hidden in the genital skin produce normal levels of androgens.
So the default state of human (and other mammals) development is women. The man's body is transformed from the male body's blueprint based on the action of androgen. A masculine organ can find a corresponding part in a woman, and vice versa. A man's nipple is equivalent to a woman's nipple without development. Of course, if a man's nipple is harmful, natural selection will make it completely disappear. Although the nipples of men are of no use, they have no harm. Some men get breast cancer, which is sometimes fatal. However, when breast cancer occurs, it often passes through the growth period, and natural selection will not eliminate it. So the answer to this question is clear: Why do men have nipples? Because women need nipples. The nipple of a man is a useless and harmless by-product to meet the needs of a woman's breast development.
A man's nipple is not a degenerate organ, but an organ that has no development. It has blood vessels, nerves, breasts, and other structures that allow it to play a lactating role. If the secretion of male and estrogen in a man's body is dysregulated, for example, when the amount of androgen secretion is reduced in old age, the man's breast will also develop. In some special cases, such as taking drugs that affect hormone secretion, some men can even secrete milk. Since men have the potential to secrete milk, why does nature not allow it to fully develop and share the responsibility of breastfeeding?
There are more than 4,000 species of mammals in existence, and about 90% of them are mating, regardless of their mating. If they are mated, they will leave. These "bad men" are certainly not likely to breastfeed. The remaining 10% of the males and females form a family and share the responsibility of raising the offspring. But since the mother's milk is enough to eat, it is not necessary for the father to breastfeed together, let them go out for food to take food home, or defend the territory, the role is greater. Among all mammals, only one male (Diyak fruit foxes distributed in Malaysia and neighboring islands) will lactate under natural conditions. We do not know whether these male milks are also used to feed offspring, probably because they are The food that is eaten contains a high concentration of phytoestrogens, so it stimulates the secretion of milk and has no use.
Men do not breastfeed because it is not necessary. This is the result of different evolutionary strategies adopted by both sexes. Of course, we humans can change the fate of evolution through modern medical technology. It would not be unimaginable if there was a "daily dad" in the community one day. Meditech