Judith N. answered • 06/21/19
Biology Major specializing in Global Health and Infectious Diseases
This is a very interesting question. I would presume that first and foremost, the hair would be essential for warmth.
However, as we know, armpit and pubic hair begin to grow during puberty, and not before. While we do not completely know whether humans can actually produce pheromones that could alter the behavior of other humans, what is certain is that apocrine glands become functional during puberty. Apocrine glands (https://health.howstuffworks.com/wellness/men/sweating-odor/apocrine-sweat-glands1.htm) are responsible for producing sweat during times of heightened emotional activity, including but not limited to stress and sexual arousal. Sweat produced by apocrine glands travels through the hair follicles and to the skin, where it interacts with the present flora to produce an odor/scent.
From this information, I would gather that from an evolutionary perspective, armpit hair would serve as an indicator of one's state. If sweat is produced as a result of sexual arousal, then it would make sense that armpit and pubic hair begin to grow and apocrine glands become functional during puberty. This could alert members of the opposite sex whether or not one is aroused, and an appropriate response would follow. This of course, is a hypothetical explanation based on my knowledge of evolution and the human body.
