Why does modern man have much more hair in a number of body places (such as head, armpits, pubic area) than elsewhere on the body?

Answer

The period that man can be called “modern” is very short compared to the much longer period in which our ancestors lived in natural conditions. In that evolutionary history of our species, certain traits were selected that offered advantages to our ancestors.

As for general body hair, our ancestors lost their body hair to allow sweating through sweat glands in the skin. This is an adaptation to very active movement, walking or walking great distances to gather food and hunt, in the hot African savanna. Hair on the scalp protects against sunstroke in our species’ characteristic upright walking, in the area where our species originated – the African savanna.

Hair in armpits and pubic area serves to diffuse pheromones, the musky scent intended to stimulate sexual attractiveness and activity.

Beard growth is probably a signal that the man is sexually mature and qualifies as a partner for the woman, and for reproduction. Incidentally, beard growth – like other places where hair growth differs between male and female (chest, legs, etc.) – is very different among ethnic groups (in biology “populations”). In some countries eg in Asia, American Indians, Inuit and in Africa there are populations of people with very little beard growth and male body hair. This indicates sexual preference for a particular phenotype that can vary widely between populations. eg. in the Mediterranean area women may have previously preferred men with strong beard growth, while in Northern Europe the opposite was the case.

We have inherited those characteristics that were vital to our ancestors, or important for optimal reproduction. In our ancestors they came about during an evolutionary history of hundreds of thousands of years, while our modern period is at most a few thousand years.