It is accepted that the detailed mechanisms of changes in human hair growth patterns are poorly understood. It is this uncertainty that has encouraged many charlatans to operate in this area. From my perspective as an engineer, however, there is a simple mechanism that makes sense of these changes. I suggest this mechanism is closely connected with the evolution and function of hair. The fact that the presence of this mechanism can be demonstrated in the male pattern baldness scenario, raises a number of serious questions relating to fundamental physiology and the mechanisms of some serious diseases. As an amateur, it is difficult for me to gain access to up-to-date research data, so my references are derived from textbooks. I would therefore welcome comments from professionals who are involved in the areas indicated in this paper.