 Another philosophical issue raised by population genetics is reductionism. It is often argued that the population-genetic view of evolution is inherently reductionistic, by both its critics and its defenders. This is apparent from how population geneticists define evolution: change in gene frequency. Implicit in this definition is the idea that evolutionary phenomena such as speciation, adaptive radiation and diversification, as well as phenotypic evolution, can ultimately be reduced to gene frequency change. But do we really know this to be true? Many biologists, particularly ‘whole organism’ biologists, are not convinced, and thus reject both the population-genetic definition of evolution and the primacy traditionally accorded to population genetics within evolutionary biology (Pigliucci 2008).