264 SCIENCE PROGRESS 



the late Lord Kelvin dogmatically asserted that geologic time 

 must be compressed within ioo millions of years, Darwin was 

 seriously perturbed, not so much on account of the truth of the 

 crucial fact of evolution, as of his own particular theory of 

 natural selection. The cause for alarm has now been removed, 

 but it still remains true that the subjects of geologic time and of 

 methods of evolution are closely interrelated. 



If we consider the interrelation from the biological standpoint, 

 and endeavour to ascertain what light can be thrown on our 

 subject with the aid of the bare facts of that science, we discover 

 that very little information is available. We soon find ourselves 

 arguing in a vicious circle. We know (for example) that man 

 has developed from a pithecanthropoid form since the Pliocene, 

 and that the horse has evolved from a beast with five small hoofs 

 on each spray foot since the early Eocene. But if we desire to 

 state the time in figures, we can only say that the Pleistocene is 

 the period that has been required to develop man, and that man 

 has developed during the Pleistocene. The biologist has no 

 independent standard of time. Vague as are the data of the 

 geologist, those of the biologist are still more uncertain. 



It is, of course, possible to utilise the fact that no considerable 

 natural change has been observed, during the historical period, 

 in any organic form, and from this fact to posit a minor limit. 

 Here, however, the Mendelian theorist, who has been so 

 prominent of late years, will assert that evolution proceeds by 

 jerks, and that the observed forms of life are in the resting 

 phase. Improbable as such speculations may seem, there are no 

 plain and obvious facts by which they can be refuted, so, here 

 again, the biologist is referred to geological data. As in the 

 time of Kelvin and Huxley, so to-day, it still remains for those 

 who deal in physical and geological data to find the measure of 

 time to which the biologist must fit his theories. There is so 

 much theory in modern biology. 



A number of biologists, of whom Prof. Poulton is the most 

 prominent, admit this statement, so far as it deals with known 

 fossiliferous rocks, but express the opinion that biologists can 

 confidently assert that these represent but the last phase of an 

 evolution which represents a vaster vista of time, an evolution 

 of which all record has been lost. 1 As Prof. Poulton has shown, 

 all the known phyla of the animal kingdom are found in the 



1 Essays on Evolution, pp. 1-45. 



