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

4 - Human variation: chronic diseases, risk factors, and senescence


Humans interface with their physical environment through a complex series of biocultural mechanisms. This range of interaction allows a wide variation in phenotypes. Humans use culture so extensively that inclinations for complex symbolic communication and patterns of social interaction may be genetically programmed as are the physical and neurological structures on which these activities depend (Durham 1991). Inter-individual communication allowing experiences to be retained across generations provides opportunities to inhabit a variety of ecological settings. Therein, local populations may develop both biological and social/cultural/behavioral variability while responding to environmental and sociocultural circumstances. Such local adaptive responses allow populations to differ significantly in phenotype from others residing elsewhere (Crews and Bindon 1991). All populations tend to maintain relatively constant living environments that provide human needs for food, shelter, reproduction, and infant/child care, and promote survival of their members. This similarity across multiple external environments allowed humans to maintain a 99.5% genetic similarity across their range. Although cultural systems alter local populations by restricting mate choice and concepts of ideal mates, thereby producing socioculturally determined selection, wide-ranging human populations remain a single interbreeding species, unlike many wide-ranging non-human groups (Lasker and Crews 1996). Humans all share the same physiology and basic life history, and remain susceptible to the same internal processes of senescence. With larger numbers of individuals surviving to their later decades of life, this similarity is revealed as a senescing soma that loses function across multiple integrated systems associated with chronic degenerative processes. Local selective pressures (e.g., malaria, cold, hypoxia, solar radiation, plant toxins, viruses, bacteria) produce variations in behavioral, sociocultural, and biological responses across populations, but the underlying degenerative processes remain the same.

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