 His answer to the question of what a gene is, is that a gene is evolutionary just insofar as it is something heritable that is subject to rates of selection that exceed the mutation rate. This is a definition, not a discovery. If it is favorably or unfavorably selected and heritable, it is an evolutionary gene. According to this definition, items that are not made of DNA can be classed as evolutionary genes so long as they match Williams’ definition (Lu &amp; Bourrat 2018).