Units of Selection

For natural selection to proceed there must be heritable variation in phenotypes and the variation in phenotype must be associated with differential survival and/or reproduction (must be differential fitness). Then, any entities exhibiting heritable variation in rates of reproduction can evolve. In terms of entities that can be heritable we can consider genes, chromosomes, genomes, individuals, groups, demes, populations, species, etc. Each of these entities meets the requirements of units that can be acted upon by selection. Selection act on all levels the important unit of selection depends.