The Significance of Mendelism for Evolutionary Theory: a re-assessment

It is well-known that the rediscovery of Mendelian genetics at the turn of twentieth century offered Darwin's theory a much-needed lifeline, by showing how Fleeming Jenkins’ famous “blending” objection could be rebutted. However, Mendelism has another fortuitous consequence for evolutionary biology that is less widely appreciated. By bequeathing the notion of allelism to biology, Mendelism shows how two difficult conceptual issues for evolutionary theory can be resolved. The first issue concerns the notion of population. By definition, evolutionary change is change in the composition of a population, but what is the relevant definition of “population”? The second issue concerns Darwin's notion of “struggle for existence.” Is this struggle an essential part of evolution by natural selection or not? In a Mendelian population, these issues can be simply resolved, since the selective competition is at root between alleles at a locus, who are necessarily playing a zero-sum game, rather than between organisms, who may or may not be doing so.