EVOLUTION 501 



complex descriptions by more comprehensive and simpler 

 descriptions — to discover in variation, growth, and heredity, 

 facts which can be described by a few formulae, nay, if 

 possible, by one brief formula. And now that quantitative 

 methods — as accurate as those of the physicist — are 

 being applied to life, we need not despair of rapid pro- 

 gress in this direction. 



As to the problem of evolution itself, we are learning 

 to see it under a new light. Natural selection combined 

 with sexual selection and heredity is actually at work 

 changing types. We have quantitative evidence of its 

 effects in many directions. The problem of evolution 

 can no longer be parodied by asking,^ " What is to secure 

 that two individuals of opposite sexes in the primeval 

 forest who have been both accidentally blessed with the 

 same advantageous variation shall meet, and transmit by 

 inheritance that variation to their successors ? " Varia- 

 tions do not occur accidentally or in isolated instances ; 

 autogamic and assortative mating are realities, and the 

 problem of the near future is not whether Darwinism is a 

 reality, but what is quantitatively the rate at which it 

 is working and has worked. If that problem should be 

 answered in a way that is not in accordance with the age 

 of the earth as fixed by certain physicists, it by no means 

 follows that it is biology which will have to retrace its 

 steps. When the rate is determined, it will be as exact 

 in its nature as physical appreciations ; and it will be a 

 question of superior logic, and not of the superiority of 

 the " exact " over the " descriptive " sciences which will 

 have to settle any disagreement of biology and physics. 



This is, however, for the future ; in the present the 

 unsolved problems are, indeed, fairly numerous and im- 

 portant — but they are so in all branches of science. 

 Luckily the statistical method indicates in most cases a 

 direct plan of attack. Of all these problems I look upon 

 the differentiation of maximum fertility, the correlation 

 between various stages of growth in the same individual, 

 and the rapidity of the action of natural selection as 



1 Presidential Address ; British Association, Oxford, 1894. 



