254 TROPICAL NATURE, AND OTHER ESSAYS. 



with are the influence of locality, or of some unknown 

 local causes, in determining the colours of insects, and, 

 to a less extent, of birds ; and the way in which certain 

 peculiarities in the distribution of plants may have been 

 brought about by their dependence on insects. The 

 latter part of my address will deal with the present state 

 of our knowledge as to the antiquity and early history 

 of mankind. 



ON SOME RELATIONS OF LIVING THINGS TO THEIR 

 ENVIRONMENT. 



Of all the external characters of animals, the most 

 beautiful, the most varied, and the most generally 

 attractive are the brilliant colours and strange yet often 

 elegant markings with which so many of them are 

 adorned. Yet of all characters this is the most difficult 

 to bring under the laws of utility or of physical con- 

 nection. Mr. Darwin as you are well aware has 

 shown how wide is the influence of sex on the intensity 

 of coloration ; and he has been led to the conclusion 

 that active or voluntary sexual selection is one of the 

 chief causes, if not the chief cause, of all the variety 

 and beauty of colour we see among the higher animals. 

 This is one of the points on which there is much di- 

 vergence of opinion even among the supporters of Mr. 

 Darwin, and one as to which I myself differ from him. 

 I have argued, and still believe, that the need of protec- 

 tion is a far more efficient cause of variation of colour 

 than is generally suspected ; but there are evidently 

 other causes at work, and one of these seems to be an 

 influence depending strictly on locality, whose nature 



