Beard biology

The development of beard begins in adolescence. The growth of beard is related to the stimulation of dihydrotestosterone on facial skin hair follicles. After puberty, dihydrotestosterone continues to affect the growth of beard. Hair follicles in different skin areas are affected by hormones differently, some are stimulating and some are inhibiting. Dihydro testosterone is also the main cause of male baldness. Dihydro testosterone is obtained by the reaction of testosterone in the body. During the year, the testosterone level in the body is different in different seasons, so the beard often grows faster in summer. In the early stage of scientific research, it is difficult to quantify the growth of beard due to the limitation of technology, so there is a great controversy when studying the effect of evaluating short-term beard storage with hormone activities. For example, 1970 mentioned in a research paper published in the authoritative journal Nature that a physicist lived on an island in a remote area for several weeks, during which he was in a relatively isolated living environment. The physicist noticed that his beard had stopped growing, but it appeared again the day before he left the island. The growth rate of beard reached its peak on the first day and the second day after he returned to China. Through research, he came to the conclusion that sexual behavior may stimulate the growth of beard. However, at that time, beard researchers disagreed.

Modern scientific research shows that the growth of beard is mainly regulated by genes. Biologists regard beard as the second sexual characteristic of men, because it is unique in gender, but it does not play a direct role in reproduction. Darwin put forward a possible hypothesis about the evolution of beard for the first time in the Origin of Man: the process of sexual selection in human activities may have led to the appearance of beard. Modern biologists have confirmed the sexual selection in the evolution of beards, and they have found evidence that women tend to think that men with more beards are more attractive when choosing a mate.

In evolutionary psychology, the explanations for the existence of beard include: transmitting the signal of sexual maturity, and beard increases the visual area of chin, thus transmitting a dominant advantage. In contrast, a clean-shaven face conveys less sense of domination and dominance. Some scholars believe that if the existence of beard is caused by sexual selection, whether the reason is related to attraction (between the opposite sex) or dominance (between the same sex) needs further research and discussion.

Beard can be regarded as an indicator of the overall state of men. The amount of facial hair will affect the attractiveness of men. Beards are often caught in a fight, which is risky to their lives. Therefore, biologists speculate that beards must have other very strong evolutionary advantages to offset the negative effects brought by this risk: beards often symbolize more testosterone content in men, and high testosterone content is found to be related to immunosuppression, which is beneficial to spermatogenesis. Except for the hairless parts such as mucous membrane, palm, sole and lips, the surface of human body is covered with a lot of hair. Hair on the body surface can be divided into many types, including millihairs and male hairs, and beards belong to the latter. Each type of hair has a unique cell composition, but it generally follows the same growth cycle: growth period, regression period and rest period. In the growth cycle, the length of all kinds of hair is different, even the same kind of hair is different. Some hair follicles in the beard may be in the growth period, while others are in the rest period. When the hair follicle completes a complete cycle, it will start a new cycle again, and a new beard will be produced at this time. The growth rate of beard is about1.25cm per month.

Early stage of hair growth:

The growth period starts from nipple and lasts for 2 ~ 6 years. Which hair follicles will be in the growing period is determined by genes. The longer the hair follicle is in the growing period, the faster and longer it grows. During the growing period, the cells of the dermal papilla divide constantly to produce new beard fibers, and the hair follicles go deep into the dermis to obtain more nutrition. For hair follicles on the scalp, about 85% of hair follicles are in the growing period at any time.

Degeneration period:

Genes determine the time when hair follicles leave the growth stage and enter the retrogression stage. The retrogression period is also called the transition period. During this period, hair follicles can renew themselves, which usually lasts for 2 weeks. Hair follicle retreats, nipple and hair are separated. At this point, the hair roots lost the nourishment of blood. In extreme cases, the hair follicle can shrink to 1/6 of its original length, causing the hair roots to be pushed upward. At this time, the beard no longer grows, but the total length of the fiber is still increasing because it is constantly pushed out.

Rest period:

The rest period generally lasts 1 to 4 months. About 10%- 15% of the hair follicles on the scalp are in this period. At this time, the epidermal cells facing the hair follicle will continue to grow, thus gathering near the root of the hair, temporarily fixing the hair that has stopped growing on the skin, so that the hair can continue to play some functions without body nutrients. At a certain time, the hair follicle will re-enter the growth period, at this time, these epidermal cells will be softened, the previously temporarily fixed hair will fall off, and new hair will reappear from the hair follicle outlet within 2 weeks. The end of dormancy is the beginning of growth. This alternating process essentially leads to the normal hair shedding and renewal process. Beards are androgenic hairs, which are different from hairs and hairs. Hair is even more invisible in thickness and color. Androgen is not good for hair growth, but it promotes the development of fine hair to mature hair. Therefore, in the case of normal endocrine, compared with women, men have more body hair but are more prone to baldness. Under the action of androgen, millihairs are transformed into mature apical hairs.

Research by Ashley Montagu, a professor of anthropology at Princeton University, shows that Asians, Bushmen and blacks have less body hair and beards than whites. Montague believes that this feature of less hair is a kind of juvenile persistence. Worldwide, the distribution of body hair is different in different regions and nationalities. The darker the color, the larger the distribution area of body hair on the body surface. Rodney P.R. Dawber (a clinical researcher in dermatology) of Oxford Hair Foundation mentioned in his research that East Asian men have less facial hair (beard) and body hair. Dober also found that near the Mediterranean region, men's body hair grows very luxuriantly. Research by anthropologist Arnold Henry Savage Landau found that Ainu people have the most vigorous body hair. A study by C.H. Danforth and Mildred Trotter of the Department of Anatomy of the University of Washington among European army soldiers shows that white people with dark hair have more beards and body hair than white people with light hair. According to the paper published by H.Harris in the British Journal of Dermatology, American Indians have the least body hair, while China and blacks have very little body hair. White people have more body hair and beards than black people, while Ainu people have the most. Mirka Ne? Me? Other people's research also shows the fact that whites have more body hair than blacks. Eike-Meinrad Winkler and Kerrin Christiansen of the Institute of Human Biology in Hamburg, Germany, aim at living in Namibia and! The body hair and hormone levels of Gongxian people were studied. The results suggest that there are three reasons why African blacks have less body hair than European whites: the secretion of androgen and estradiol, the metabolism of androgen and the response of target cells to sex hormones.

Valerie Anne Randall, from the Department of Biomedicine in university of bradford, said: White men's beard growth reached its peak in their mid-thirties, because the transition from hairs to mature hair requires waiting for the growth cycle to complete the transformation. Randall found that under the same serum androgen level, white men and women have more body hair than Japanese men and women, which may be related to the different sensitivity of hair follicles to 5α- reductase during sex hormone metabolism, and the specific mechanism needs to be further clarified.

Stewart W. Hindley and Albert Damon of the Department of Anthropology at Stanford University suggested that white people (white people) have more body hair and beards than black people and Mongolian people (yellow people) (see the table below). Distribution ratio of body hair on the middle finger of human body Population ratio Andaman 0% Eskimo 1% African American 1 6%-28% Ethiopians, 25.6% Mexicans in Yucatan Peninsula, 20.9% Penobscot, 22.7% Gurkha in Nepal, 33.6% Japanese, 44.6% Indian, 40%- 38+0% European, 60%-80% Anthropologist Joseph Denik found that the people with the most beards and body hair include Ainu, Iranians and others.