I believe that Darwin wasn't really talking about birds...it was an analogy and he was in fact thinking light years ahead of his time when he came up with this idea of "survival of the fittest." He was thinking to a time when 25 million people would live in an area so small, they would be living on top of each other, literally.
Picture this, a paved 2 way road, 12 feet across that has no sidewalks and needs to allow cars, bikes and pedestrians to move from place to place. Now, where I'm from the order of right-of-way is pedestrians, bikes and then cars. Sort of makes sense....but here in one of the most populous countries in the world. Watch out, because if you expect to be given right-of-way as a walker, you just became filler for that pothole you just tried to avoid. Cars do not stop for people and bikes expect you to get out of the way. In a land where they drive on the other side of the street, they also expect you to duck and run if you see a car coming.
Survival of the fittest just became a reality for me in this urban jungle. Lions and tigers and bears oh my? Forget it. I'm worried about teeny tiny cars that my nephew could probably push around his yard in a real life game of Cars.