Document Type



Rhesus monkeys from the thirtieth day of pregnancy were fed a semisynthetic diet affording 1, 2, or 4 g protein/kg of body weight each day until delivery. They were housed in individual cages located in a screened, roofed enclosure that exposed them to normal climatic variations. The 50 infants born of these mothers were weighed and x-rayed at birth. Birth sizes were significantly affected by conception weights of the mothers, by the season in which the pregnancy occurred, and by the sex of the infants, but not by maternal protein intake. The absence of birth-size differences between the progeny of the three dietary groups suggests that compensatory factors are in operation. One important way of controlling birth size is by regulating gestation length. It is proposed that the pregnant primate with her single infant can monitor the environment and the progress of the conceptus to exercise significant control over its development.