6o A STUDY IN HEREDITY 



time it did not exist. Then, from small beginnings, 

 it grew, under the influence of selection, perhaps 

 to a great magnitude. If it becomes useless, it 

 is no longer subjected to selection, and reversion 

 sets in. Ancestors more and more remote are 

 approximated to, till, if the process be continued 

 long enough, that most ancient condition is reverted 

 to when the character did not exist. We cannot 

 trace the course of reversion among wild plants 

 and animals, for the process is slow, and our means 

 of observing it with precision is insufficient ; but 

 we know from the evidence of vestigial remains, 

 that degeneration occurs among them, and the 

 phenomena of reversion among our artificially 

 evolved plants and animals enables us to determine 

 the nature of the degeneration. 



But whether it be agreed or not that degenera- 

 tion is caused by the reappearance of the ancestral 

 type, it is agreed by all authorities that this at 

 any rate is true, that whenever a character ceases 

 to be useful it undergoes degeneration, and tends 

 to disappear. That fact is of immense importance 

 to our main inquiry. 



I have now completed the introductory portion 

 of my work, and may in comfort proceed with my 

 proper theme. The ground is cleared, and by 

 anticipation I have met some objections, which 

 would otherwise have been raised. The four main 



