A universal generative tendency toward increased organismal complexity
Characterizing internal variance as complexity needs justification, because in colloquial usage, complexity connotes so much more. A complex organism is ordinarily understood to be not just more internally varied, or more differentiated, but more capable as well. The human brain is thought to be complex not simply because it has many cell types, but because of its impressive functional capabilities, because of what it can do. Thus, as conventionally understood, complexity depends on both structure and function. However, in biology, a narrower view has been adopted, herein complexity refers to number of part types, or degree of differentiation among parts. Complexity has other aspects besides number of part types. For example, there is complexity of spatial arrangement of parts, a kind of second-order complexity (where number of part types is first order), and number of types of connections among parts. The chapter introduces three simple models to illustrate the internal-variance principle and also to reveal its robustness. In each successive model, the variations introduced are more finely tuned in such a way as to negate or overcome the internal-variance principle. © 2005 Elsevier Inc. All rights reserved.
