PROFESSOR HUXLEY'S LECTURES. 297 



evolution does require so great a time ? The biologist knows nothing 

 whatever of the amount of time which may be required for the pro- 

 cess of evolution. It is a matter of fact that those forms which I 

 have described to you occur in the order which I have described in 

 the tertiary formation. But I have not the slightest means of guess- 

 inn- whether it took a million of years, or ten millions, or a hundred 

 millions, or a thousand millions of years, to give rise to that series of 

 changes. As a matter of fact, the biologist has no means of arriving 

 at any conclusion as to the amount of time which may be needed for 

 a certain quantity of organic change. He takes his facts as to time 

 from the geologist. The geologist, taking into consideration the rate 

 at which deposits are formed and the rate at which denudation goes 

 on upon the surface of the earth, arrives at certain more or less justi- 

 fiable conclusions as to the time which is required for the deposit of a 

 certain amount of rocks, and if he tells me that the tertiary forma- 

 tions required 500,000,000 years for their deposit, I suppose he has 

 good ground for what he says, and I take that as the measure of the 

 duration of the evolution of the horse from the Orohippus up to its 

 present condition. And, if he is right, undoubtedly evolution is a 

 very slow process, and requires a great deal of time. But suppose, 

 now, that an astronomer or a physicist for instance, my friend Sir 

 William Thomson comes to me and tells me that my geological 

 friend is quite wrong, and that he has capital evidence to show that 

 life could not possibly have existed upon the surface of the earth 

 500,000,000 of years ago, because the earth would have been too hot 

 to allow of life, my reply is: " That is not my affair; settle that with 

 the geologist, and when you have come to an agreement between 

 yourselves I will adopt your conclusion." We take our time from 

 the geologist, and it is monstrous that, having taken our time from 

 the physical philosopher's clock, the physical philosopher should turn 

 round upon us, and say we are going too fast. What we desire to 

 prove is, is it a fact that evolution took place ? As to the amount of 

 time it took, we are in the hands of the physicist and the astronomer, 

 whose business it is to deal with those questions. 



I think, ladies and gentlemen, that I have now arrived at the con- ' 

 elusion of the task which I set before myself when I undertook to de- 

 liver these lectures before you. My purpose has been, not to enable 

 those of you who have not paid attention to these subjects before to 

 leave this room in a condition to decide upon the validity or the in- 

 validity of the hypothesis of evolution, but to put before you the 

 principles by which all such hypotheses must be judged; and, further- 

 more, to make apparent to you the nature of the evidence and the 

 sort of cogency which is to be expected and may be obtained from it. 

 To this end I have not hesitated to regard you as genuine students 

 and persons desirous of knowing the truth. I have not hesitated to 

 take you through arguments, even long chains of arguments, that I 



