ARTHUR, W.; University of Sunderland (UK): What determines the direction of evolutionary change?

In this presentation, I examine the deceptively simple question posed in the title. I begin with a historical approach. I look at the views of Darwin and Wallace; Fisher and Ford; Gould and Lewontin. I then pose the question: is there a current consensus view? If so, is it a pluralist or a ‘monist’ (e.g. pan-selectionist) one? I then give my personal view of what the answer should be, which involves a mixture of three things, two widely accepted and one not. The former are natural selection and historical contingency. The latter is the structure of variation in development, including both mutation bias and developmental bias. I attribute a much more substantial role to this variational structure than it is conventional to do. I will explain why I have reached this conclusion and why I believe that other biologists should do likewise. I will emphasize that my conclusion covers both situations where evolution proceeds through making use of a population’s standing variation and those where it proceeds through the occurrence of novel mutations.