Abstract

There is still a great deal of debate over what counts as a constraint and about how to assess experimentally the relative importance of constraints and selection in evolutionary history. I will argue that the notion of a constraint on variation, and thus the selection-constraint distinction, depends on two specifications: (1) what counts as a variant -- constraints limit or bias the production of what? and (2) range of assessment -- over what range of times or conditions is the variation assessed? Specifications 1 and 2 help us to understand empirical work on the relative importance of constraint and selection in evolution.