Debate about adaptationism in biology continues, in part because within “the” problem of assessing adaptationism, three distinct problems are mixed together. The three problems concern the assessment of three distinct adaptationist positions, each of which asserts the central importance of adaptation and natural selection to the study of evolution but conceives this importance in a different way. As there are three kinds of adaptationism, there are three distinct “antiadaptationist” positions as well. Or putting it more formally, there are three different dimensions here, and strongly adaptationist views, strongly antiadaptationist views, and moderate views are possible for each dimension.

Understanding the distinctions between the three adaptationist positions will not remove all controversy, but some progress can be made through clarifying the distinctions. In particular, progress can be made by recognizing that evidence against one kind of adaptationism need not also be evidence against other kinds. So the main aims of this chapter are classification and clarification. I describe the three kinds of adaptationism and then discuss the evidence relevant to each one. In particular, I try to say which problems might be solved directly through empirical research, and which are more philosophical in character.

A STATEMENT OF THE DISTINCTIONS

Here are the three kinds of adaptationism I recognize: empirical adaptationism, explanatory adaptationism, and methodological adaptationism.

Empirical Adaptationism: Natural selection is a powerful and ubiquitous force, and there are few constraints, except general and obvious ones, on the biological variation that fuels it. To a large degree, it is possible to predict and explain the outcome of evolutionary processes by attending only to the role played by selection. No other evolutionary factor has this degree of causal importance.