Human beings are mammals. One of the features of mammals is the presence of some hair on their bodies. Hair covers the entire body of some mammals. In the case of humans, hair grows only in certain parts. Body parts where the hair grows in men and women also differ. For example, beard and mustache are present only in men.
Hair protects the skin and maintains body warmth. It is sensitive to touch. The hair in the ears, nose, eyebrows and eyelashes plays the role of providing protection to these organs from dust, impurities and insects. If the purposes of hair are same, why men only have beards and are absent in women?
Androgens in men are responsible for regulation of secondary sex male features which include growth of beard, mustache and chest hair. Change in voice is another effect. The roles of estrogen result in growth of breasts, pubic hair and regulation of menstrual cycle. These hormones play other roles also. Estrogen makes the female body soft and tender. The male body becomes hard and strong because of the effects of androgen. Another group of hormones named progesterone is responsible for regulation of pregnancy in women.
Men and women belong to the same species. But different hormones are present in men and women. They play different roles in the growth of body parts and control functions of different organs. The absence of hormone androgen in women is primarily responsible for the absence of beards in women.