ABSTRACT

This chapter examines why the Ache begin reproduction when they do, and the related question about why they are the size that they are. As individuals grow they increase in body size with a resultant greater net energy production which can be channeled into fertility or survivorship. The body size and sexual maturity models allow for some speculation. The Ache fitness curve as a function of male body weight decreases sharply after about 65 kg primarily because the curve relating fertility to body weight also shows a sharp decrease at about the same place. Growth patterns represent the solution to a trade-off between decreasing survival to reproductive age and increasing survival or fertility after maturity. The consumption of energy is an increasing allometric function of body weight, with the power being less than one. Mammals are characterized by a pattern of determinate growth. The time spent growing delays sexual maturation and thus lowers the probability of surviving to reproductive age.