Life-history theory = understand ways in which the stages of life and the associated behaviors are organized. Look at ultimate causes for developing these traits. First need to determine ecology of typical ancestral population. Then decide if changing environment was responsible for evolution of a particular trait. There was no clear-cut ancestral ecology so used african village (1950-1975). Emphasis was placed on picking population with strong social dynamic. Look at stages of human life history through ecology perspective. Evolutionary ecologists predict that human life history is unique because of our large brain. Other primates have much smaller brains relative to body size. Selection pressures influencing mortality and fertility favor particular life-history strategies. Grandmother hypothesis: women stop reproducing to help their own kids reproduce. Parents can start weaning (stop breastfeeding) sooner and grandmother can take care of kid so mom can get kid 2 going. Grandmother being present lowers average child bearing age of mother by 1.