Board Thread:Suggestions forum/@comment-32918765-20171030193812/@comment-26149161-20171105142800

You're assuming that the change will be random and be good for everyone. For example, a dog that grew wing-stumps would not be fit to survive, and almost certainly wouldn't. But in other (insect) species, due to luck or more rapid adaptation, wing-stumps could grow and mutate into wings. That's on the largest end of the spectrum, though--most changes are far smaller. However, the stacking of those small changes is the true thing that leads to large-scale evolution.

Take dinosaurs. Feathers were initially a mutation in the gene, which became a form of display and heating tool. Over time, their arms became able to flap and support themselves in the air, leading to flight. As we can see, these changes are usually not so simple as "the dog grew wings". There's a lot of elements that go into this stuff, and it isn't just a "Boom. You have wings."

Ithilion, Discussions Moderator (Auta i lómë)