* [[Professor Rowan]] is said in the games to have studied Pokémon evolution and determined that 90% of all Pokémon are related in some way by evolution. As of [[Generation
VII]], with 146 Pokémon out of 809 total not evolving, this is only slightly inaccurate, as a little under 82% of all Pokémon undergo at least one evolution before being fully evolved. In previous generations:
** 25 out of 151 Pokémon did not evolve in Generation I, meaning 83% of all Pokémon undergo at least one evolution.
** 43 out of 251 Pokémon did not evolve in Generation II, meaning 83% of all Pokémon undergo at least one evolution.
** 104 out of 649 Pokémon did not evolve in Generation V, meaning 84% of all Pokémon undergo at least one evolution.
** 115 out of 721 Pokémon did not evolve in Generation VI, meaning 84% of all Pokémon undergo at least one evolution.
By far, a plurality of three-stage evolution families were introduced in Generation I, with 27 such families having their roots there (though not necessarily their most unevolved or most evolved forms). Because of branch evolution, 29 of the second-evolution Pokémon can count themselves as members of a Generation I evolution family. Generation V has the second most, with 19 three-stage families (none due to branching). Generation III has the next most, with 16 three-stage families that end in 18 Pokémon (again due to branching), while Generations II, VI, VII, and IV have the least, with only nine, eight, eight, and six families, respectively, that end in a third member.
** Generation V, however, has introduced the most original three-stage evolutions, as many of the three stage-evolutions stemming from Generation I include Pokémon not introduced in the same generation as their evolutionary relatives.
* Generation VII is the only generation to introduce Legendary and Mythical Pokémon that are a part of an evolutionary family.