At the risk of sounding obtuse, I'm puzzled by some aspects of the course of evolution.
I read that vertebrates - reptiles, birds - are descended from bony fish that came out of the seas and became adapted to life on land. It said that some reptiles evolved into birds, but that the two front legs evolved into wings. But what must have these reptiles done in order to evolve into birds and for the two front legs to have evolved into wings?
By contrast, in some mammals - like humans, it said - the front legs evolved into arms. But, like the fish 400 million years ago that came out of the sea via their bony fins, thus gradually evolving into amphibians etc., what must these mammals have started doing so that their front legs evolved into arms?
I'm just struggling to get it clear in my head exactly where adaptation, the actions of an animal or chance variations come into play and have an influence in the course of the evolution of species.
I read that vertebrates - reptiles, birds - are descended from bony fish that came out of the seas and became adapted to life on land. It said that some reptiles evolved into birds, but that the two front legs evolved into wings. But what must have these reptiles done in order to evolve into birds and for the two front legs to have evolved into wings?
By contrast, in some mammals - like humans, it said - the front legs evolved into arms. But, like the fish 400 million years ago that came out of the sea via their bony fins, thus gradually evolving into amphibians etc., what must these mammals have started doing so that their front legs evolved into arms?
I'm just struggling to get it clear in my head exactly where adaptation, the actions of an animal or chance variations come into play and have an influence in the course of the evolution of species.