Classical population genetics describes how the fate of an allele is driven by four forces: mutation, migration, selection and drift. However, these are sometimes insufficient to explain how the observed allele frequency changes and, therefore, another factor must be invoked: cultural transmission of fitness (CTF). CTF is the non-genetic transmission of any kind of behaviour that affects reproductive success. There are several clearly documented examples of CTF, and theoretical studies have shown that it affects effective population size, linkage disequilibrium and coalescent times. It is therefore a factor that must be taken into account to explain the structure of genetic diversity. In this article, we will present documented cases of how CTF affects the genetic diversity of populations and yields dramatic changes in allele frequencies.