Another kind of complexity

In Chapters 7 and 8 we looked at the situation of an individual faced with a complex environment, and described some conditions under which it is best for the individual to meet this environmental complexity with a complex organic response. This is not the only type of organic system which can be complex or simple; another is the population. This chapter is about population-level responses to environmental complexity, and the relation between individual-level and population-level responses.

Complexity in the case of individuals was understood as heterogeneity. Complexity in populations will be understood the same way. A complex population is one which contains a diversity of types or forms. A simple population is homogeneous. The models of Chapters 7 and 8 examined a particular kind of individual-level complexity: the ability of an individual to do a variety of different things in different circumstances. In this chapter we will look at a particular case of population-level complexity: heterogeneity or “polymorphism” in the genetic make-up of the population. We will also investigate the relations between two different realizations of biological complexity, the relations between (i) simple populations of complex individuals, and (ii) complex populations of simple individuals.

The first part of this chapter is only indirectly relevant to the environmental complexity thesis. The aim is an understanding of a pattern of externalist explanation of complexity in biology, and certain work on genetic polymorphism will be discussed as a case study.