Check if one Pokémon is evolutionarily related to another Pokémon

[Motas]

So I'm working on modifying the Dubious Clause that is found in Mej71's Challenge Modes/Uranium Nuzlocke Scripts. I have a question on a particular problem that I've run into.

$PokemonGlobal.nuzlockeMaps.push([$game_map.map_id,1]) if ($PokemonGlobal.dubiousClause  && !@battlers[1].owned)

Instead of checking @battlers[1].owned, I want to check all forms of that pokemon (i.e. all evolved stages).

For example. Let's say I caught a Poliwhirl in the wild and I ended up running into a Poliwag on a later route. I don't own a Poliwag, but the dubious clause will count that Poliwag as the first Pokemon on the route, so if I miss it, I won't be able to catch another. I want the if statement to count Poliwag as owned since I already have a Poliwhirl.

So how do I check for something like the following:

$PokemonGlobal.nuzlockeMaps.push([$game_map.map_id,1]) if ($PokemonGlobal.dubiousClause  && !in_array(evolutionArray(@battlers[1])))

in_array() is just a function I know in PHP, I'll end up looping through it or doing something similar in Ruby if I need to, this is just for the example's sake.

If there is already a predefined method available, I would like to know what it is. If not, a hint on how to start would be great. I'm learning how to code in Ruby so I don't need the answer given to me. I just need to know where to start looking.

Thanks in advance!