THE EVOLUTION OF THE BIRD
the wrist into a single element and a corresponding fusion of the two bones of the forearm.
But the adoption of a life in the air not only requires a modification of the physical structure of the wings and body but affects the relative importance and even the character of the senses as well as of the brain that makes use of the information they afford. The sense of smell becomes much less useful to a flying animal than it was to a crawling animal, which carries its head so close to the ground that it can recognise the presence of other animals by the odours which they leave behind them. We therefore find that the nose of a bird—its sense of smell—is in no way better than that of a crocodile.
In order to utilize fully the improved senses and to adjust them delicately to the conditions on which flight depends modifications must be made in the structure of the brain. The brain of a bird consists of the same parts as that of a crocodile and resembles it very closely in its fundamental arrangement, but that part (the cerebellum) which coördinates the muscular movements and adjusts them to the conditions under which the bird finds itself is much larger and is more complicated in structure. The part of the brain that is concerned with vision is larger, and the part that is concerned with smell is smaller.
More important in some respects is an enlargement of the front part of the brain to enable the bird to bring together there all the information that comes to it from its senses and to decide on its behaviour in the light of the memories of past events that are stored there. It is to the development of this part of their brains that birds owe all those competencies in building their nests and in caring for and protecting their young which have long endeared them to moralists.
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