Natural selection is an important force that shapes the evolution of all living things by determining which individuals contribute the most descendents to future generations. The biological unit upon which selection acts has been the subject of serious debate, with reasonable arguments made on behalf of populations, individuals, individual phenotypic characters and, finally, individual genes themselves. In this essay, I argue that the usual unit of selection is the gene. There are powerful logical arguments in favor of this conclusion, as (...) well as many real-world examples. I also explore the possibility that epigenetic differences between individuals may be heritable between generations. Although few such examples exist, epigenetic differences provide an exciting source of potentially heritable variation that may allow rapid evolutionary change to occur, perhaps in response to environmental influences. (shrink)

This chapter contains sections titled: Introduction Natural Selection Operates within Genomes without Regard for Phenotypic Effect Selective Forces, Heritable Variation, and the Definition of Function Natural Selection Can, and Does, Act on the Products of Individual Genes Natural Selection Can Act Directly on Genes Themselves What Are the Limitations on the Unit of Selection Being “the Gene”? The “Complexity” Argument: Do Complex Phenotypes Require Complex Explanations? Do “Epigenes/Epialleles” Provide a “Non‐genetic” Source of Heritable Variation Upon Which Natural Selection May Act? (...) Summary Points: The Usual Unit of Selection Is the Gene Postscript: Counterpoint Note References. (shrink)