400 SCIENTIFIC THOUGHT IN THE NINETEENTH CENTURY. 



some of the Greek philosophers. Just at the beginning of our cen- 

 tury Lamarck developed the idea of evolution into something like a 

 scientilie 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 systematist or the embryologist, 

 the geographer or the paleontologist; but each and all found the path 

 to any credible theory of organic evolution blocked by the stubborn 

 fact that variations in species appeared everywhere to be limited in 

 degree and to oscillate about a central average type instead of becom- 

 ing cumulative from generation to generation. In the Darwinian 

 principle of natural selection for the hrst time was suggested a force 

 whose existence in nature could not be doubted, and whose tendency, 

 conservative in stable environment, progressive in changing environ- 

 ment, would account at once for the permanence of species through 

 long ages and for epochs of relatively rapid change. However Dar- 

 win's work maj' be discredited by the exaggerations of Weismannism, 

 however it may be minitied by Xeo-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 Newton's discovery of universal gravitation has pro- 

 duced so profound an effect upon the intellectual life of mankind. 

 The tombs of Newton and Darwin lie close together in England's Val- 

 halla, and together their names must stand as the two great epoch- 

 making names in the history of science. 



Darwin's discovery relates primarily to the origin of species I)}' 

 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 maj^ reasonably follow in our thinking, provided only 

 we bear in mind that she is a treacherous guide and sometimes leads 

 astray. Conclusions that rest only on analogy nmst be held tenta- 

 tively and not dogmatically. Yet it would be an unreasonable excess 

 of caution that would refuse to recognize the direction in which anal- 

 ogy points. When we trace a continuous evolution from the nebula 

 to the dawn of life, and again a continuous evolution from the dawn 

 of life to the varied flora and fauna of to-day, crowned, as it is, with 

 glory in the appearance of man himself, we can hardly fail to accept 

 the suggestion that the transition from the lifeless to the living was 

 itself a process of evolution. Though the supposed instances of spon- 

 taneous generation all resolve themselves into errors of experimenta- 

 tion, though the power of chemical synthesis, in spite of the vast 

 progress it has made, stops far short of the complexity of protoplasm, 

 though we must confess ourselves unable to imagine any hypothesis 



