SCIENCE IN THE LAST HALF CENTURY. 85 



in living beings, which nil admitted as a matter of fact, the selective 

 influence of conditions, which no one could deny to be a matter of fact 

 when his attention was drawn to the evidence, and the occurrence 

 'of great geological changes which also was matter of fact, could bo 

 used as the only necessary postulates of a theory of the evolution of 

 plants and animals which, even if not, at once, competent to explain all 

 the known facts of biological science, could not be shown to be incon- 

 sistent with nuy. So far as biology is concerned, the publication of the 

 " Origin of Species," for the first time, put the doctrine of evolution, in 

 its application to living things, upon a sound scientific foundation. It 

 became an instrument of investigation, and in no hands <lid it prove 

 mo're brilliantly profitable thaFi in those of Darwin himself. His pub- 

 lications on the effects of domestication in plants and animals,. on the 

 influence of cross-fertilization, on flowers as organs for effecting such 

 fertilization, on insectivorous plants, on the motions of plants, pointe<l 

 ont the rontes of exploration which have since been followed by hosts 

 of inquirers, to the great profit of science. 



Darwin found the biological world a more than sufficient field for 

 even his great powers, and left the cosmical part of the doctrine to 

 others. Not much has been added to the nebular hypothesis since the 

 time of Laplace, except that the attempt to show (against that hy])Oth- 

 €sis) that all nebulae are star clusters, has been met by the spectro- 

 scoi)ic proof of the gaseous condition of some of them. Moreover, phy- 

 sicists of the present generation appear now to accept the secular cool- 

 ing of the earth, which is one of the corollaries of that hypothesis. In 

 fact, attempts have been made, by the help of deductions from the data 

 of physics, to lay down an approximate limit to the number of millions 

 of years which have elapsed since the earth was habitable by living 

 beings. If the conclusions thus reached should stand the test of further 

 iuvestigption, they will undoubtedly be very valuable. But, whether 

 true or false, they can have, no influence upon the doctrine of evolu- 

 tion in its application to living organisms. The occurrence of succes- 

 sive forms of life upon our globe is an historical fact which can not be 

 disputed, and the relation of these successive forms, as stages of evolu- 

 tion of the same type, is established in various cases. The biologist 

 has no means of determining the time over which the process of evolu- 

 tion has extended, but accepts the computation of the physical geologist 

 :and the x^hysicist, whatever that may be. 



Evolution as a philosophical doctrine applicable to all phenomena, 

 •whether physical or mental, whether manifested by material atoms or 

 by men in society, has been dealt with systematically in'the "Synthetic 

 Philosophy" of Mr. Herbert Spencer. Comment on that great under- 

 taking would not be in place here. I mention it because, so far as I 

 iknow, it is the first attempt to deal on scientific principles with modern 

 scientific fiicts and speculations. For the " Philosophic positive" of M. 

 Comte, with which Mr. Spencer's system of philosophy is sometimes 



