48 EXPERIMENTAL EVOLUTION LECT. 



has allowed natural selection to operate, and allows 

 us to expect to push things further in the way of 

 direct experiment. 



I do not intend to recall here all the facts which 

 have been quoted by a large number of naturalists, up 

 to the present day. I shall merely call attention to 

 the most important of them, using again preferably, 

 as they may be less familiar to my hearers, those 

 which I have been able to collect from French 

 sources. 



One of the variable characters in most living beings 

 is colour, in most, not in all, for there is among the 

 human races a strong tendency to the preservation of 

 the race-colour, while among animals, and especially 

 plants, colour varies a great deal. And this is the 

 reason why Linnaeus wrote his ever-quoted nimium 



II. Physiological variations. 



Variations through diminished activity. Lateness of develop- 

 ment ; enfeeble - 

 ment of sexual ten- 

 dencies ; sluggish- 

 ness. 



earlier Precocity. 



exaggerated Increase in fertility, 



etc. 



stronger Vigour ; immunity 



from diseases, etc. 



To this list, as I shall show later on, we must make an important 

 addition in Group II., and add what I propose to call physiological or 

 chemical variation, although it differs entirely from the sort of variation 

 included by Cornevin under the same name 



