Andrew Morrison, of King's High School, asks :-
Why do we have hair in only certain places?
Nick Lewis-Barned, an endochrinologist at the Otago Medical School, responded.
The answer to this can be thought of at several different levels. Firstly the presence of hair is the distinctive feature of mammals. It is not true to say that we only have hair only in certain places. In keeping with virtually all mammals, we have hair all over our bodies but it is simply thicker and longer in some areas than others.
The principle influences of hair growth are of cellular differentiation in the skin, giving some cells greater sensitivity to factors which promote hair growth than other skin cells. Men and women differ principally in their exposure to different hormones so that exposure to male hormones (androgens) result in the typical male hair distribution while exposure principally to oestrogens results in the female hair distribution. This of course can be reversed by hormonal manipulation and from time to time medical interventions can cause this.