Physical, hormonal and behavioural aspects of sexual development in the marmoset monkey, Callithrix jacchus.

Measurements of growth, plasma progesterone and testosterone levels, and copulatory behaviour were obtained from captive marmosets from birth until 600-800 days of age. Body weight and knee-to-heel length were similar for both sexes. Males exhibited a neonatal testosterone surge from 15-100 days and testosterone levels began to rise again, coincident with the growth of the testis, at about 250 days. The males were copulating by 400-500 days of age. Paired females were apparently ovulating and able to conceive from about 400 days. In peer groups, only the dominant female became pregnant, because subordinate females failed to ovulate.