12 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



relations of the present to the past inhabitants of that 

 continent. These facts, as will be seen in the later 

 chapters of this volume, seemed to throw some light on 

 the origin of species — that mystery of mysteries, as it has 

 been called by one of our greatest philosophers." 



" On my return home it occurred to me (in 1837) that 

 something might perhaps be made out of this question by 

 patiently accumulating and reflecting on all sorts of facts 

 which could possibly have any bearing on it. After five 

 years I allowed myself to speculate on the subject, and 

 drew up some short notes ; these I enlarged (in 1844) into 

 a sketch of the conclusions which then seemed to me 

 probable ; from that period to the present day I have 

 steadily pursued the same object. I hope I may be 

 excused from entering on these personal details, as I give 

 them to you to show that I have not been hasty in coining 

 to a decision." 



Darwin founded his theory of " Natural Selection " on 

 four axioms : — 



1. That no two plants or animals are identical in all 

 respects. 



2. That the offspring tend to inherit the peculiarities of 

 their parents. 



3. That of those who come into existence, few reach 

 maturity. 



4. That those on the whole best adapted to the circum- 

 stances in which they are placed are the most likely to 

 leave descendants. 



It is an easily observed fact that in every generation of 

 every species, far more individuals are born than can 

 possibly survive, so that there is a constant battle for 

 life going on amongst all organic beings. In this struggle 

 for existence, those individuals, which are best fitted, by 

 any slight variation, which can be of use in the struggle, 



