CONCLUSION 



CTARTING from the origin of matter, we have now arrived 

 ^ at the realization of the human form, linking these two 

 extremes by a continuous chain of facts, solidly riveted by 

 careful arguments based on a small number of principles. 

 Most of these principles were formulated long ago, discussed 

 and then abandoned, because they were first stated in a general 

 form and afterwards discovered to be inadequate. Each, 

 however, had a value of its own, and it was only necessary to 

 give them intelligent co-ordination in order to obtain a rational 

 explanation of Life and its activities. 



It is undoubtedly true, as Cuvier x had already insisted in 

 opposition to many of his contemporaries, and as Pasteur 

 has since triumphantly demonstrated, that the spontaneous 

 generation of living beings no longer occurs in Nature ; but it 

 has been equally well demonstrated that the sun alone can 

 sustain life on earth, and that if the sun were extinguished 

 life would vanish with it. But this makes it probable that life 

 was born from rays which the sun has lost, 2 but which we may 

 now actually hope to produce by artificial means, thus opening 

 the door to the realization of the wildest anticipations. It is 

 also true that the variations in plant and animal species are so 

 gradual, or so slight when they are sudden, that we might 

 suppose their forms to be fixed, as the majority of naturalists 

 once believed; yet these variations do nevertheless take place, 

 and, slow though they may be, we can, by expending great 

 care, induce plants to vary from their original condition. But 

 time is needed, and in the days when Cuvier defended the fixity 

 of species, no one considered the shortness of the period during 

 which we have made any observations at all, as compared 

 with one of the geological periods whose history we have been 

 able to reconstruct. 



Lamarck attributed the variations of species to habits 

 imposed upon animals by the stimuli of their external 



1 Regne animal, 3rd edition, vol. i, p. 9. 



2 Cf. p. 70. 



