Biology, culture and the environment

The word population may have different meanings to distinct specialists. The point to be emphasized, however, is that it has structure. When the question is asked about how populations change in size over time (mainly a historical question), both intrinsic and extrinsic factors should be considered. In most general terms population behavior depends on individual behavior, that in turn is adjusted in a complex way by both genetic and environmental factors. The latter may comprise the physical environment, with its variables of temperature, humidity and general geologic conditions; or the socioeconomic system, developed by our cultural skills, which can also serve as a buffering layer that protects us from the rigors of the outside world.

Members of a Mendelian (sexual and cross-fertilizing) population have sex, and the proportion between males and females (the sex ratio) may significantly influence its future. People are born and die, and factors related to fertility, morbidity and mortality should also be considered. People also move (with the exception of those who already died!), and intra- and interpopulation mobility should be taken into consideration. In evolutionary terms, these different agents ultimately condition the opportunity for the action of natural selection, leading to the survival of the genetically best endowed and the elimination of those with lower ‘fitness’.

Ideally, concepts from the several areas of knowledge mentioned above should closely interact, to obtain answers to the problems raised by different aspects of population fate. Unfortunately they seldom act this way. Good examples of such interactions, however, can be found in the works of Harrison and Boyce (1972), Ward and Weiss (1976), Harrison (1977), Adams et al. (1990), and Boëtsch et al. (1996).