What doesn't make sense to me, like many others have said in this topic, why did the Zora need to evolve if the land was flooded. They are already excellent swimmers and this type of world best suits their physical features.
However, once they gained the ability to fly, Darwinism would say that because the swimming capabilities of the Rito were now obsolete, their survival was based solely on flying skill. While they didn't inherit wings as genetics and rather, were given them, they would never grow their own wings, but their 'fins' for swimming would probably disappear over the long haul. I suppose their beaks also formed because of survival of the fittest. Maybe the beak helps their flying capabilities, so those with poor or no beak slowly died off while the dominant beak Zora/Rita survived.
I suppose I'm probably over analyzing the Darwinism aspect of evolution. Either way, I wasn't quite happy with the Rito tribe evolution, if it even really is an evolution and not a completely different tribe. I'd much rather have them be different species all togethor. As a Zelda fan, the bigger the better, the more the marrier. Thus, rather than 'eliminating' one race to create another, they should have just introduced a whole new race (which they possibly even did so). I'd love to believe that and in future games see the Zora and Rito both in the same game, much as I'd like to see several of the other so called 'evolved' races blend in as well. A game with 10-12 different races would be sweet.