GREAT STEPS IN ORGANIC EVOLUTION 879 



enough, light enough, and mobile enough to serve as wings? An 

 answer — certainly not unreasonable — is that the primitive winglets 

 served as surfaces on which the air-tubes were spread out, thus 

 securing more effective respiration, and also as parachutes for 

 gliding when the Proto-insects were so disposed. 



THE ORIGIN OF BIRDS.— The appearance of birds, in Triassic or 

 Jurassic Ages, was one of the great events in animal evolution. Like 

 the rise of insects, it expressed a new emancipation, for typical birds 

 broke the tether that binds most life to earth. And while the Flying 

 Dragons or Pterodactyls, and the Bats, of much later origin, also 

 solved the problem of true flight, the feathered wing stands quite 

 by itself, not comparable with the skin wing of Pterodactyls and 

 Bats, and totally distinct from the chitinous outgrowths of insects. 



We take the origin of birds as an illustration of a kind of problem 

 of which we can give only two or three instances — that of the 

 pedigree of a particular type. It may be noted at the outset that the 

 case of bird-pedigree brings out very clearly the strength — and the 

 remaining weakness, too — of the evolutionist way of looking at 

 things. As to the strength, every competent zoologist is convinced 

 that primitive birds emerged millions of years ago from some stock 

 of extinct reptiles. As to the weakness, every careful zoologist will 

 hesitate before committing himself to a statement in regard to the 

 particular group of extinct reptiles from which birds took origin. 

 He will make negative statements to the effect that it could not have 

 been the Pterosaurs, nor the Iguanodons, or their like, that were 

 birds' ancestors. Moreover, if he goes the length of saying, as many 

 have done, that birds sprang from an "Ornithischian" group of 

 bipedal Dinosaurs, he will probably add: "But by what factors the 

 change came about, I know not." 



Returning to the first proposition, that birds sprang from a stock 

 of extinct reptiles, it may well be asked why zoologists are so sure 

 of this. For it is a very startling conclusion that the soaring creatures 

 of the air are the scions of a stock that crept or plodded on the 

 earth. No two adjacent classes seem more sharply contrasted than 

 do reptiles and birds. 



We quote two paragraphs, expressive of this contrast, from 

 Heilmann's Origin of Birds (London, 1926): — 



"Every move of the bird is characterised by its warm pulsating 

 blood; its passions are strong, and its feeling so intense as to find 

 expression in song. Its gait is upright; powerful wings lift it without 

 apparent effort into the highest regions of the air; and thence it is 

 able to descend to the earth with the utmost speed, protected by its 

 warm plumage from the greatest variations in temperature; while 

 its vision may be adjusted instantaneously to any distance, thus 

 enabling it, with equal ease, to sight its quarry from afar or near. 



