| Abstract: |
This is an article which attempts to provide a background to the study of human adaptation. Adaptation is defined as the functional response of an organism or populations to the environment. Adaptation results from evolutionary change (specifically, as a result of natural selection) and is closely bound to biological models, health, and ecology. These changes are on three primary levels: genetic, developmental, short-term. Adaptation is closely linked to "fitness" as many studies deal with the reproductive success of a population in a particular region of the world. Fitness can be studied three ways: through an evolutionary context of reproductive success, the health status and well being (biobehavioral fitness) which are linked to developmental and short-term patterns of adaptation, or lastly, to the ability to perform sustained work or exercise (physiological fitness). The standard studies from which attempts to demonstrate that a population has found "the ability to adapt" to a particular environment are broad studies such as adaptations to temperature, altitude, growth and development, disease, and nutrition. Studies have been based on three different approaches to demonstrate this concept. The first is something possessed by the individual, such as adaptation to heat, second is adaptation as a state of being (e.g., high altitude), and lastly, as a process (acclimation and acclimatization). The ability to successfully respond environmental stress (heat, cold, altitude) revolves around the concepts of "stress" and "strain." Stress is define as the force causing the body to react to new pressures to the body, while strain, is the body's reaction, either favorable or unfavorably, to an environmental stimulus. Heat is the example provided. It illustrates both a negative feedback (of a physiological response that is beneficial to the person and also a positive feedback which detrimental. The negative feedback causes a decrease in body temperature through sweating but the alternative response is dehydration as a result of sweating. Another type is on the growth and development of the people. The term growth refers to an increase in mass or number of cells, whereas development refs to the differentiation of cells in to the different types of tissues and their maturation. There are two essential approaches to the study of growth and development: the adaptability model and the medical model. The adaptability models identifies growth as a facilitator or as the means of adaptation to the environment. The medical model, on the other hand, dictates growth as a measure of adaptation. Stated another way, if a child grows slowly, the child is either adaptively responding to disease or limited nutrition (adaptive model) or is just poorly adapted to this environment (medical model). While both approaches use the same methodology it is the type of questions being asked by the researcher that will determine the type of model used. The adaptive model would be used more by scientists interested in human adaptation and evolution will use more the adaptive model while typically health care researchers interested in applied health and growth will typically apply a medical model. Work on human response to infectious disease involves the co-evolutionary transformation of host/parasite resistance that may include genetic changes in both organisms or adaptations at other levels. Multiple factors affect the possible responses to infectious disease. These factors include genetic adaptation by resistance and susceptibility, developmental factors in resistance (behavioral, health, and immune status), and short-term adaptation factors linked to health. The emotional status has also been shown to affect the immune system. Research on the importance of adequate nutrition have been a major focus of the study of adaptation. Covariant and co-adaptive relationships with nutrition include growth, resistance to disease, reproduction, physical work capacity and strength, thermoregulation, learning, and emotionality. These may play a major or minor role in people's biological requirements as determined by age, sex, and reproductive, physiological, or activity status. In recent years a multidisciplinary approach to studies of adaptation have been undertaken. These have allowed greater insights to the myriad of possible factors that influence adaptation change that would not be available otherwise from a single investigator. As noted in the article, multidisciplinary studies are more expensive in the long run they are less expensive per research output due to the economy of sharing ideas. It is stressed that in order to substantially contribute toward our understanding of human biological and behavioral responses greater cross-disciplinary collaboration will need to be undertaken. It is important that anthropologists, instead of focusing on questions that only attempt to show WHY a particular response has occurred, they need to begin to ask HOW this complex relationship between environment and people's response to the environment came into being in the first place.
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