xlii Centennial An7iiversari/ 



of evolution was held by some of the* Greek philosophers. Just 

 at the beginning of our century Lamarck developed the idea of 

 evolution into something like a scientific theory. 



Yet it is no less true that the epoch of evolution in human 

 thought began with Darwin. Manifold suggestions there were of 

 genetic relationships between different organisms, whether organic 

 forms were studied by the systeraatist or the embryologist, the 

 geograplier or tlie paleontologist ; but each and all found the path 

 to any credible theory of organic evolution blocked by the stub- 

 born fact that variations in species appeared everywhere to be 

 limited in degree, and to oscillate about a central average type, 

 instead of becoming cumulative from generation to generation. 

 In the Darwinian principle of natural selection, for the first 

 time, was suggested a force, whose existence in nature could not 

 be doubted, and whose tendency, conservative in stable environ- 

 ment, progressive in changing environment, would account at 

 once for the permanence of species through long ages, and for 

 epochs of relatively raj^id change. However Darwin's work may 

 be discredited by the exaggerations of Weismannism, however it 

 may be minified by Neo-Lamarckians, it is the theory of natural 

 selection which has so nearly removed the barrier in the path of 

 evolution, impassable before, as to lead, first the scientific world, 

 and later the world of thought in general, to a substantially unani- 

 mous belief in the derivative origin of species. Certain it is that 

 no discovery since ISTewton's discovery of universal gravitation has 

 produced so profound an effect upon the intellectual life of man- 

 kind. The tombs of jSTewton and Darwin lie close together in 

 England's Yalhalla, and together their names must stand as the 

 two great epocli-making names in the history of science. 



Darwin's discovery relates primarily to the origin of species by 

 descent with modification from preexisting species. It throws no 

 direct light upon the question of the origin of life. But analogy 

 is a guide that we may reasonably follow in our thinking, provided 

 only we bear in mind that she is a treacherous guide and some- 

 times leads astray. Conclusions that rest only on analogy must 

 be held tentatively and not dogmatically. Yet it would be an 

 unreasonable excess of caution that would refuse to recognize the 

 direction in which analogy points. When we trace a continuous 

 evolution from the nebula to the dawn of life, and again a con- 



