CREATION BY EVOLUTION
In this account of the origin of the birds I have dealt only with certain selected parts of the body, and with only a few of the changes in the conditions of life. For example, I have not referred to the modifications of structure that are needed to enable a bird to perch on a twig. The features that I have mentioned were selected because they can be explained without presenting too much detail, and because they show the retention in birds of features whose presence is due to their existence as useful modifications of like features in their reptilian ancestors. The points considered may be summarized as follows:
1. The bird owes the presence of two, three, four, or five phalanges, or joints, in its toes to the fact that its reptilian ancestor, owing to its straddling gait, required toes that increased in length from the first to the fourth, whereas in the bird the second toe, which has three phalanges, and the fourth toe, which has five, are actually of the same length.
2. The bird owes the anomalous manner in which its aorta crosses from the left to the right side of the center of the body to the fact that in reptiles only this one of the pair of aortae transmits pure blood.
3. The bird owes its possession of only the first three fingers and not, as might have been expected, the fourth and fifth fingers, to the fact that the first three fingers are those which are most useful in the reptilian ancestor for clasping food between the two hands.
4. The bird owes the character of its brain to its descent from an animal having a brain like a crocodile.
This list might be extended indefinitely, but these four examples are sufficient to show that the peculiarities of the bird’s structure—the points in which it seems to be clumsily constructed—are at once explained as relics derived from its reptilian ancestor.
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