The theme for day 20 is "baby" pokemon. The idea of a baby pokemon was another afterthought added in subsequent versions of the game, but it raises questions. When a pokemon evolves, is it reaching a higher level of power? Does evolution have something to do with sexual maturity? It must, otherwise the baby pokemon themselves could mate with each other.
Also, is it possible to create new species of pokemon by crossbreeding existing species? Is that how they got from 150 to 600-whatever they're at now?
Either that or it's an effort for them to just make existing pokemon cuter, to encourage people to buy further variations of the game.