THE EVOLUTION OF THE BIRD
tions under which soaring flight is possible, and those aviators who have flown engineless aeroplanes (gliders) for hours at a time have been copying the eagles and giving us valuable information about the difficulties of the process, the chief of which is perhaps the recognition of the upward-directed currents of air on which it depends.
The other difficulty, the inability of the aeroplane to fly very fast or very slowly, depends on the long tail that all present-day aeroplanes have. As soon as it becomes possible to control an aeroplane that has no tail, or a very short one, man may be able to copy the manoeuvers of the eagles. From this point of view Archaeopteryx corresponds to a present-day aeroplane, the modern birds to the aeroplane of the future. It is certain that Archaeopteryx was clumsy, incapable of hovering over one spot and of alighting on a definite perch.
Archaeopteryx was therefore far inferior to the modern birds (see fig. 3) in its power of flight. It was clumsy, ill constructed, and lacked that perfection of form and motion which makes the sea gull a constant source of delight. Is it credible that a bird that was miraculously created in a moment should be so imperfect? Is not the imperfection of its machinery an evidence of evolution? Is it not more reasonable to recognize in Archaeopteryx a necessary stage in the long process by which a crawling reptile was gradually converted into the perfect flying bird of to-day?
I have here tried to bring together facts about the birds that bear witness to their evolution from more primitive ancestors. Comparative anatomy, embryology, and palaeontology unite in telling the same story. They agree in testifying that the bird is to-day a highly specialized descendant of some reptilian ancestor. Is it at all probable that there has been collusion among these witnesses and that their testi-
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