Do some evolutions require defeating Alphas?

The lock is species-specific. The Alpha you have to beat is the Alpha variant of the same creature you want to evolve, so clearing a different Alpha somewhere else does nothing for it. Until that fight is done, the evolution requirements cannot be met at all. A creature sitting at the right level with everything else in order will simply stay in its current form.

That makes Alpha hunting part of raising certain lines rather than optional side content. The fights are not a pure tax, though. Alpha bosses drop loot on top of opening the evolutionary path, so the trip pays for itself even for a species you were not planning to evolve.

Most evolutions are not like this. The usual trigger is reaching a certain level, and the Alpha requirement sits in the smaller group of evolutions with special conditions attached.

The other special evolution conditions

Alphas are one of several gates. Some Aniimo only evolve when traded to another player, which means that form is off the table if you are playing alone. Others branch instead of running in a straight line, giving you two path options decided by the quest choices you make and the items you have collected.

So when a creature refuses to evolve at the level you expected, the question is which of these it uses: an Alpha to defeat, a trade to arrange, or a branch whose conditions you have not met yet.

Not settled: Which Aniimo have Alpha-gated evolutions is not fully settled yet, so treat a stalled evolution as a prompt to check that species rather than assuming an Alpha fight is waiting.