CREATION BY EVOLUTION 



extended the distance covered in these leaps by stretching 

 out their freely movable fore legs so that they acted like the 

 wings of an aeroplane and came to support more and more 

 of the weight of the body. Their value as wings may have 

 been greatly increased by the fact that they were already 

 covered with feathers, which formed a fringe along the 

 hinder edge of the arm, exactly as the scales do to the hind 

 leg of a crocodile. The use of the fore legs as wings in this 

 way, however, merely supports the front end of the body 

 and head and leaves the tail trailing behind. But just as 

 scales cover the whole of a lizard so feathers covered the 

 whole of the bird ancestor, including its tail, and if these 

 feathers retained the arrangement which they had as scales 

 and followed the crocodile pattern they formed lateral keels 

 along that organ. These keels will also act as wings, and if 

 they become large enough are quite capable of supporting 

 the weight of the hinder half of the animal. 



Even after the bird ancestor had progressed to the point 

 where it could rapidly move by a series of leaps, whose length 

 was increased by gliding, while it gained speed by an 

 increase in the power of the hind legs, the transition to true 

 flight was a great step, which depended on the adoption of 

 a flapping action of the wings. Such flapping, to be effec- 

 tive, must be regulated in a definite way, the course taken 

 by the wing in its down stroke being different from that 

 which it follows as it is brought up again to begin a new 

 stroke. This perfect regulation of flight can be most easily 

 assured by so shaping all the faces by which the bones move 

 on one another and so arranging the ligaments by which 

 they are tied together that no other movements are possible. 

 In the modern birds this end is accomplished with great 

 perfection by an arrangement that results in the fusion of all 

 the originally separate bones of the palm of the hand and 



[248] 



