By inference then, any entities exhibiting heritable variation in rates of reproduction can evolve .
Nature is organized in a hierarchical fashion.
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. First, some historical context. Populations have their own rates of origination and extinction and selection could thus operate at the level of the group. In general selection at the level of the individual would be much stronger than selection at the level of groups.