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  • Print publication year: 2003
  • Online publication date: August 2009

3 - Human variation: growth, development, life history, and senescence

Summary

Many emphasize the uniqueness of humans among animals, while others see them as simply another mammal in the order primates. To understand current patterns of life and death, one must first examine human evolutionary history, the type of creatures from which we evolved, how their adaptations shaped their ancestors' physiology and function, and how these led to our current long lives and extended infant, child, adolescent, reproductive, and late-life periods compared with other similarly sized primates (Figure 3.1). Over the past several million years, hominids (hominins; members of the family Hominidae including bipedal primate mammals, and modern humans and their immediate ancestors and relatives) have comprised a primate group that was relatively terrestrial and mobile and likely exploited marginal environments for subsistence, while, over time, adopting a material–cultural life style (Dunbar 1988; Hunt 1994). Most primates are omnivorous, what set later hominids apart was the inclusion of gathering/scavenging/hunting in their behavioral repertoire. Given a reliance on marginal environments with scattered resources, early hominids may have experienced strong selective pressures for enhanced memory (remembering landmarks and resources), group cohesion (recognizing relatives and kin), and communication skills. Extension of life stages and life span improves such traits by allowing enhanced opportunities for learning through experience and for retaining group knowledge. These various trends coincided and co-evolved during hominid and, ultimately, human evolution. Specific patterns of inter-relationships among these trends remain unclear.