Why organisms live, have so many life spans. Not all organisms age in the same way that we age. = branch of evolutionary biology devoted to explaining variation in reproductive strategies. Bats survive ~30 years, yearly reproduction once mature. Brown antechinus one breeding season, then dies. By the end of the season, all their hairs fall out, they"re riddled with parasites and they die. California poppy, flower in 1 season, then die. Offspring almost the size of their parent when they are born. 1 clutch every 2 weeks, as long as they are fed. Born inside the mother, mates inside the mother w/ a sibling. Evolution by natural selection leads to traits that increase lifetime reproductive success relative to conspecifics. Facts: limited supply of e/nutrients (resources) available to organism, limited time available for biological processes. Organisms must balance competing demands for time and energy.