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SCIENCE 



[N. S. Vol. XXV. No. 631 



potent in changing the bearings of paleon- 

 tology upon the doctrine of evolution. 



In Darwin's two chapters on geology 

 in the 'Origin of Species,' he marshaled 

 with great skill the geological facts then 

 known which appeared favorable to evolu- 

 tion. Yet he recognized in the facts of 

 paleontology ' perhaps the most obvious and 

 serious objection which can be urged 

 against my theory.' He cited a long list 

 of recognized authorities in geology and 

 paleontology, still living or recently dead 

 at the time of the publication of his first 

 edition, who were believers in the immu- 

 tability of species — Cuvier, Agassiz, Bar- 

 rande, Pictet, Falconer, Forbes, Lyell, 

 Murchison, Sedgwick. Of these Lyell 

 alone lived to become a convert to evolu- 

 tion. 



Of course the objection which Darwin 

 felt so strongly himself, and which seemed 

 conclusive to so many paleontologists at 

 the time, was the absence of gradation 

 between different forms. The theory of 

 evolution, and especially the strictly Dar- 

 winian form of that theory, requires fine 

 gradation between species — not indeed be- 

 tween different species now existing, but 

 between existing species and species now 

 extinct, and between fossil species of suc- 

 cessive periods. In general, such grada- 

 tions do not appear. Fossil species are 

 about as sharply defined as recent ones; 

 and whole groups of species — orders, 

 classes, sub-kingdoms — have appeared 

 without recognizable ancestry. Darwin's 

 answer to this objection was given in the 

 phrase now become classical, 'the imper- 

 fection of the geological record.' 



In the half-century since the publica- 

 tion of Darwin's first edition, the attitude 

 of paleontologists has completely changed. 

 Not only is it true at present that paleon- 

 tologists are substantially unanimous in 

 accepting the doctrine of evolution; but it 

 has come to be generally believed that the 



very science which afforded a half-cen- 

 tury ago the strongest objection to evolu- 

 tion now affords its strongest support. 

 This change is in large part due to the 

 discoveries which have so shattered the ob- 

 jection that once appeared so strong. In- 

 numerable links then missing have been 

 brought to light. Intermediate forms be- 

 tween orders and classes formerly sup- 

 posed to be widely separated from each 

 other have been discovered in great 

 abundance. Numerous series of genera 

 may be traced through successive geo- 

 logical periods, exhibiting a gradually pro- 

 gressive change which almost irresistibly 

 suggests to the mind the belief that the 

 series are truly genetic. The fossils of our 

 western plains have afforded a goodly share 

 of the most important of these new evi- 

 dences of evolution. 



When the first edition of the 'Origin 

 of Species' was published, the classes of 

 birds and reptiles seemed to stand widely 

 asunder. But in the very next year (1860) 

 an odd feather of Archseopteryx was dis- 

 covered, and a year later the skeleton now 

 preserved in the British Museum. But 

 Archffiopteryx was a solitary representa- 

 tive of the birds of markedly reptilian char- 

 acter until the discovery of Ichthyornis 

 and Hesperornis in the Cretaceous of 

 Kansas, of which preliminary descriptions 

 were published by Marsh in 1872. Both 

 these remarkable types show reptilian 

 affinities, in the possession of teeth, in the 

 structure of the skull (though unhappily 

 the palatal region is but imperfectly 

 known), and in the pelvis; and Ichthyornis 

 very notably in its slightly biconcave ver- 

 tebrae, contrasting strongly with the saddle- 

 shaped articulating surfaces of the ver- 

 tebra of modern birds. However strongly 

 these genera suggest the idea of an evolu- 

 tionary connection between reptiles and 

 birds, their own place in the evolutionary 

 series is not easy to determine. Ichthy- 



