Evolutionary Model of Pubertal Maturation and Adult Reproductive Behavior in Human Males

Benjamin Campbell, Boston University
Kenneth Campbell, University of Massachusetts at Boston

The timing of male adolescent maturation is hypothesized to be the critical link between male reproduction and other physiological systems. The hypothesis is developed with reference to the Turkana, pastoral nomads of Northern Kenya among whom male puberty comes late (at 16 years) but boys continue to grow into their early 20s. Two separate physiological mechanisms are implicated. Lower fat stores alter the adrenal gland toward cortisol rather than DHEA, delaying the onset of puberty. Low caloric intake also blocks the development of secondary sexual characteristics and leads to slow though continued bone growth. One consequence of high cortisol is behavioral inhibition, possibly in social interactions with females, contributing to less promising adult reproductive strategies. Over the course of human evolution, better nutrition has led instead to earlier puberty, giving some males an edge in interactions with the opposite sex and eventually in fertility.