Historical Rules · 3 May 2019
Rule 702.99a
Official source text from the 3 May 2019 Rules release
Evolve is a triggered ability. “Evolve” means “Whenever a creature enters the battlefield under your control, if that creature’s power is greater than this creature’s power and/or that creature’s toughness is greater than this creature’s toughness, put a +1/+1 counter on this creature.”