354 NATURAL SCIENCE. December, 



who are authorities on more than one. Professor Poulton is a 

 geologist as well as a zoologist ; he was, therefore, doubtless wdse in 

 choosing a subject which depends on the evidence of both sciences. 

 His text was one of the arguments used by Lord Salisbury at Oxford. 

 It may be remembered that the Premier, in his Presidential Address, 

 claimed that the limitations placed on the age of the earth by Kelvin 

 and Tait were a proof that evolution had been physically impossible. 

 Evolution demands many hundred million years ; physics prove that 

 no more than ten or a hundred million years can be allowed. This 

 conclusion has recently been attacked by Professor Perry, who has 

 shown that of the three arguments on which it once rested, the only 

 one to which any weight was still attached is utterly valueless. He 

 has shown that Lord Kelvin's case rests on a series of assumptions, 

 which are not only unproved, but of which the truth is almost 

 impossible. Professor Poulton quotes Darwin to the effect that 

 " Thomson's views of the recent age of the world have been for some 

 time one of my sorest troubles," and that to his mental vision their 

 author was "an odious spectre." In this judgment Darwin was truer 

 than he knew ; for Perry's examination of Lord Kelvin's assumptions 

 has shown that Darwin troubled himself needlessly ; the argument, 

 as mathematically stated, is at first sight as unintelligible and alarm- 

 ing as a spectre, but it is as harmless. Perry's position is based on 

 mathematical reasoning, of which the principles are simple, but the 

 language obscure to the non-mathematical mind. Professor Poulton 

 has done a useful service by summarising the controversy in non- 

 technical language which anybody can understand. 



The second part of the address considers the biological evidence 

 in support of the geological view of the immense antiquity of the 

 earth. Professor Poulton's thesis is that the evolution of the ancestor 

 of each of the higher animal phyla probably occupied a very long 

 period, and that the time required for the evolution of the separate 

 phyla from their original common ancestor can only be expressed as the 

 period represented by all the fossiliferous rocks multiplied many 

 times over. He points out that in the Cambrian period most of the 

 hard bodied phyla were represented, and that in most cases, e.g., the 

 echinoderms, they were as distinct and separate as at present. He 

 therefore demands a prodigious period of time before the Cambrian, 

 during which life was slowly evolving. That he is right in his main 

 contention no geologist is likely to deny, although when we come to 

 his individual arguments we may doubt whether some of his estimates 

 are not exaggerated. Even if we were to accept the exceeding slow- 

 ness of evolution that finds favour with Professor Poulton, we might 

 still maintain that it advanced far more rapidly in pre-Cambrian 

 times, for groups in their youth vary more than in maturity, though 

 perhaps less than when in decay. Brooks has suggested causes as 

 likely to have accelerated the early development of the phyla, which, 

 when once well established, remained remarkably stable. Hence, we 



