Adaptation and adaptability

Adaptation and adaptability are central concepts in biological anthropol￾ogy because they are the processes whereby beneficial relationships between humans and their environment are established and maintained. 

They are also the processes that alIow change or accommodation to new conditions or circumstances. Adaptation has been considered from four perspectives: genetic, physiological, behavioural and cultural (Ellen, 1982; Harrison, 1993). 

Genetic adaptation takes place through selection of the genotype, the genetic structure of the popUlation being shaped by differential fertility and mortality. Physiological adaptation involves the shorter-term changes which individuals show in response to any of a variety of environmental stressors, among them low food availability. 

Behavioural adaptation includes types of behaviour that can confer some advantage, ultimately reproductive. Such behaviours may include proximate determinants of reproductive success, including patterns of resource acquisition, especially food and energy. Cultural adaptation involves the transmission of a body of knowledge and ideas, objects and actions being the products of those ideas. Although cultural structures can evolve as adaptive systems in response to environmental factors, not all aspects ofculture can be assigned adaptive significance (Morphy, 1993). 

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The four types of adaptation do not exist in isolation from each other. Rather, they are linked across time and feed back on each other (Fig. 1.1). Genetic adaptation takes place across generations, as do many aspects of cultural adaptation. In this sense, genetic and cross-generational cultural adaptation can be regarded as codes. Adaptation as process arises out of' adaptation as code and includes physiological and behavioural adaptation. The physiological processes have a basis in genetics, while the processes that have a basis in culture are the behaviours that operate within the lifespan of the individual. They range from the extremely short-term behaviours, such as instantaneous decisions. to longer-term behaviours, such as the choice of marriage partner. If either physiological or behavioural processes serve to enhance reproductive success, either directly or indirectly, then they can become fixed in the genetic and cultural codes, respectively. 

Thus there is feedback between processes and codes: physiological processes operating within the lifespan feed back on genetic code, influencing genetic adaptation, while behavioural processes, also taking place within the lifespan, feed back on cultural code. Behaviour and culture also influence genetic adaptation through, for example, kinship patterns and marriage laws which may affect differential reproductive success and biologial population structure through assortative mating. Furthermore, behaviours may influence physiological processes, while the diffusion of culture that has not evolved cross-generationally but has been adopted from another group or population is ofincreasing importance in a world in which the transmission of information across traditional barriers is ever increasing. 

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Although there is considerable overlap between definitions of human adaptation and adaptability (Ulijaszek, I 995), adaptability does not overlap with genetic adaptation. Furthermore, adaptability is also the ability to adapt. However, to be ofsome analytical value, it is important to define the limits of this ability, whether it be physiological, behavioural or cultural adaptation. From Fig. 1.1, it is clear that there are adaptive processes that· take place across generations, and processes that occur within the lifespan but have influence on. or drive. cross-generational processes. The term adaptability has from the outset been reserved for the kind of responses that individuals make to changes in their environment that facilitate their survival and reproduction and is thought of as a property ofan extant group (Harrison, 1993).

Figure 1.1. can be redrawn to include human adaptability as a within-generational process (Fig. 1.2) and adaptation as a cross-generational process. Thus, human adaptability includes physiological and behavioural processes, as well as the adoption of cultural factors that may be of adaptive significance from other popula￾tions. There may also be behavioural adaptability in the choice of what cultural factors are adopted.

For example, physiological responses to low dietary energy availability include weight loss and body composition changes, as well as possible down-regulation of basal metabolism. Once body size matches energy resources, homeostasis is regained at a lower level of intake. However, a behavioural response might be to reduce physical activity. These are not mutually exclusive, and the mix of physiological and behavioural adapta￾bility is constrained by cultural and genetic codes and states nested in both higher and lower levels of organisation than that of the individual. 

At a lower level, the physiological state of different organs and tissues will determine the ability of the individual to undergo weight loss without functional impairment. In the maintenance of individual physiological homeostasis, there are circumstances in which a reduction in physical activity may be preferable to weight loss. This may, however, be in conflict with strategies suggested at higher levels of organisation, such as the group or community. For example, the need to perform arduous time-limited seasonal tasks such as planting or harvesting of crops to ensure food supplies for the coming year may rule out the possibility of red uced activity in the face of low food availability.