Focus of the chapter:
- Categorization of human variation
- Study of human growth, development, and aging
- Evolution of human strategies for survival and reproduction
- Human adaptations to cold, hot, and high-altitude environments
- Influence of nutrition on all stages of the human life cycle
Race is not a biologically meaningful concept, but it has a long history within anthropology. Anthropologists began to challenge the concept of race in the early 1900s. Today, modern anthropologists focus on clines, or variations, categorized according to geographic gradients.
Human variation can be studied in terms of the human life cycle or life history and encompasses conception through aging (the postreproductive years). The stages in human life are the prenatal stage, the postnatal stage, and the adult stage. By examining biological changes at each stage in the life cycle, we can better understand such important human traits as large brain size and the long postreproductive phase.
Unlike the nonhuman primates, humans survive and reproduce within a cultural context. Some theories, such as the grandmothering hypothesis, focus on humans’ long postreproductive period within the evolutionary context of caring for children, which gives longevity an evolutionary advantage.
Adaptation to environments can take four different forms. Genetic adaptation occurs at the population level. Developmental adaptation occurs at the individual level during growth and development. Acclimatization takes place at the individual level and occurs at any point during an individual’s lifetime. Cultural adaptation refers to the use of material culture to adapt to the environment.
Humans are able to adapt to heat stress through sweating and vasodilation, due to evolution in tropical environments. Genetic adaptations in body size and shape (Allen’s and Bergmann’s rules) can also be seen in humans. Clinal variation in skin color associated with solar radiation is also seen. Humans deal with cold stress though vasoconstriction and changes in basal metabolic rate. The high-altitude stress of hypoxia (low oxygen levels) results in a range of adaptations from genetic (large chest cavity) to acclimatizing (production of extra red blood cells).
Nutrition exemplifies the biocultural nature of humans: food intake both influences and is influenced by cultural practices. The majority of human populations face increasing undernutrition (fewer than 2,000 calories per day), whereas other nations face epidemics of overnutrition (diets in excess of average daily requirements).