All mammals have some hair on their bodies and man is also a mammal. In some mammals hairs cover the whole body but in humans, hairs grow only in certain parts.
Hairs on our body preserve the body warmth and protect the skin and body openings. They also help us in realizing the sensation of physical touch. The hair on our eyebrows and eye lashes, ear and nose help guard these body cavities against dust and insects.
Now the question is, why do men have beards, and women do not? This can be understood as follows. When a child is born, he has only fur like hair on the body.
As he grows, hair becomes harder. Boys and girls reach puberty at the age of 11 to 13 years. There is faster growth of sex glands at this age. In man, the testes and other sex glands, produce a group of hormones known as ‘androgens’. In woman, the ovaries and other sex glands, produce another group known as ‘estrogens’. The function of the androgens is to regulate secondary male sex features such as the growth of facial and chest hair and deepening of the male voice at puberty. The function of the estrogens is to regulate secondary female features, such as the change in the size of breasts, growth of pubic hair and onset of the menstrual cycle. There are various other changes in men and women brought about by these hormones. For example female body becomes soft and tender whereas, male body turns hard and strong. A special group of hormones called the ‘progestrogens’; are responsible for the regulation of pregnancy. Hence women do not have beards due to the absence of androgens.