xxiv] SIR CHARLES LYELL 419 



possible origination, so early as the Miocene, was due to 

 my " want of appreciation of the immensity of time at our 

 disposal, without going back beyond the Newer Pliocene." 



To this objection I replied (May 24) as follows : " With 

 regard to the probable antiquity of man, I will say a few 

 words. First, you will see, I argue for the possibility rather 

 than for the necessity of man having existed in Miocene 

 times, and I still maintain this possibility, and even pro- 

 bability, for the following reasons. The question of time 

 cannot be judged of positively, but only comparatively. We 

 cannot say a priori that ten millions or a thousand millions 

 of years would be required for any given modification in man. 

 We must judge only by analogy, and by a comparison with 

 the rate of change of other highly organized animals. Now, 

 several existing genera lived in the Miocene age, and also 

 anthropoid apes allied to Hylobates. But man is classed, 

 even by Huxley, as a distinct family. The origin of that 

 family — that is, its common origin with other families of the 

 Primates — must therefore date back from an earlier period 

 than the Miocene. Now, the greater part of the family 

 difference is manifested in the head and cranium. A being 

 almost exactly like man in the rest of the skeleton, but with 

 a cranium as little developed as that of a chimpanzee, would 

 certainly not form a distinct family, only a distinct genus of 

 Primates. My argument, therefore, is, that this great cranial 

 difference has been slowly developing, while the rest of the 

 skeleton has remained nearly stationary ; and while the 

 Miocene Dryopithecus has been modified into the existing 

 gorilla, speechless and ape-brained man (but yet man) has 

 been developed into great-brained, speech-forming man. 



" The majority of Pliocene mammals, on the other hand, 

 are, I believe, of existing genera, and as my whole argument 

 is to show how man has undergone a more than generic 

 change in brain and cranium, while the rest of his body has 

 hardly changed specifically, I cannot consistently admit that 

 all this change has been brought about in a less period than 

 has sufficed to change most other mammals generically, except 

 by assuming that in his case the change has been more 



