Institute of Human Origins, School of Human Evolution and Social Change, Arizona State University
March 26, 2015 8:00, Grand Ballroom D
Life history theory explains variation in the pace of life as the outcome of how selection operates on a series of trade-offs in the allocation of an organism’s energetic budget. Mammalian life histories lie along a spectrum with endpoints termed “live fast, die young” and “live slow, die old.” Human life history incorporates elements of both schedules: long gestation, altricial offspring, enlarged brains, slow maturation rates, increased lifespan, and protracted periods of offspring dependence suggest a “live slow” strategy, whereas relatively early weaning, short interbirth intervals, and the ability to overlap births (resulting in the presence of multiple offspring) suggest a “live fast” schedule. Understanding when, and under what conditions, selection assembled this unique package of life history attributes is central to reconstructing the ecological, demographic, and energetic constraints that have shaped what it means to be human.
In this review, I highlight what is known, unknown, and perhaps unknowable about the evolution of hominin life history by synthesizing data from studies on extantprimate biorhythms, dental development, isotopic and dietary ecology, reproductive biology, and comparative energetics. Combined data suggest that models reconstructing all early hominins as possessing apelike life histories are likely too simplistic and ignore subtle differences in how large-bodied, large-brained apes differentially allocate energetic resources to reproductive scheduling (weaning) and overall growth. A model will be presented demonstrating that varying life history strategies likely characterized major australopith groups and early/later species of Homo, and were tuned to localized differences in diet, ecology, and energetic budgets.