Risks of childbirth increase for both early teens, first pregnancy, and for older women, and after multiple pregnancies. Hence natural selection always encounters physiological risks. .Mating can be socially delayed, and available mates restricted, by cultural practise, controlled by elders, in societies close to their ecological carrying capacity. Tribal warfare seems one such means of population blood letting, also a characteristic of apes. A trend to earlier female puberty onset, noted by some, with suspects of environment estrogens from chemicals, also limits the fully grown adult height.