4 Darwin's Predecessors 
of what occurs in the case of domestic animals and cultivated plants, 
and by his elaboration of the theory of Natural Selection, which 
Alfred Russel Wallace independently stated at the same time, and of 
which there had been a few previous suggestions of a more or less 
vague description. It was here that Darwin’s originality was greatest, 
for he revealed to naturalists the many different forms—often very 
subtle—which natural selection takes, and with the insight of a 
disciplined scientific imagination he realised what a mighty engine of 
progress it has been and is. 
(IV) As an epoch-marking contribution, not only to Atiology 
but to Natural History in the widest sense, we rank the picture 
which Darwin gave to the world of the web of life, that is to say, of 
the inter-relations and linkages in Nature. For the Biology of the 
individual—if that be not a contradiction in terms—no idea is more 
fundamental than that of the correlation of organs, but Darwin's 
most characteristic contribution was not less fundamental,—it was 
the idea of the correlation of organisms. This, again, was not novel; 
we find it in the works of naturalists like Christian Conrad Sprengel, 
Gilbert White, and Alexander von Humboldt, but the realisation of 
its full import was distinctively Darwinian. 
As Regards the General Idea of Organic Evolution. 
While it is true, as Prof. H. F. Osborn puts it, that “‘ Before and 
after Darwin’ will always be the ante et post urbem conditam of 
biological history,” it is also true that the general idea of organic 
evolution is very ancient. In his admirable sketch From the Greeks 
to Darwin’, Prof. Osborn has shown that several of the ancient 
philosophers looked upon Nature as a gradual development and as 
still in process of change. In the suggestions of Empedocles, to take 
the best instance, there were “four sparks of truth,—first, that the 
development of life was a gradual process ; second, that plants were 
evolved before animals; third, that imperfect forms were gradually 
replaced (not succeeded) by perfect forms; fourth, that the natural 
cause of the production of perfect forms was the extinction of the 
imperfect”.” But the fundamental idea of one stage giving origin:to 
another was absent. As the blue Aigean teemed with treasures of 
beauty and threw many upon its shores, so did Nature produce like a 
fertile artist what had to be rejected as well as what was able to 
survive, but the idea of one species emerging out of another was not 
yet conceived. 
1 Columbia University Biological Series, Vol. 1. New York and London, 1894. We 
must acknowledge our great indebtedness to this fine piece of work. 
2 op. cit. p. 41. 
