130 HISTORY OF BOTANY 



Huxley's resume is as follows : " Observation proves 

 the existence among all living beings of phenomena of 

 three kinds, denoted by the terms heredity, variation, 

 and multiphcation. Progeny tend to resemble their 

 parents ; nevertheless all their organs and functions are 

 susceptible of departing more or less from the average 

 parental character ; and their number is in excess of 

 that of their parents. Severe competition for the means 

 of living, or the struggle for existence, is a necessary 

 consequence of unUmited multiplication ; while selection, 

 or the preservation of favourable variations and the 

 extinction of others, is a necessary consequence of severe 

 competition. ' Favourable variations ' are those which 

 are better adapted to surrounding conditions. It follows, 

 therefore, that every variety which is selected into a 

 species is so favoured and preserved in consequence of 

 being, in some one or more respects, better adapted to its 

 surroundings than its rivals. In other words, every 

 species which exists, exists in virtue of adaptation, and 

 whatever accounts for that adaptation accounts for the 

 existence of species." 



Wallace's epitome is in the form of a table consisting 

 of two parallel columns, the first containing proved facts ; 

 the second, legitimate deductions from these facts, which 

 deductions are afterwards transferred to the first column 

 as proved facts. The table has at least the merit of 

 placing vividly before you the fundamental principles 

 on which the whole theory rests, although you must 

 bear in mind that each sentence really stands for a volume. 

 It is more in the nature of a guide to a library than a key 

 to any one volume in it. Starting with the two acknow- 

 ledged facts, (i) that organisms left to themselves increase 

 at an enormously rapid rate, and (2) that, despite this, 

 the total number of individuals at any given time remains 

 on the whole stationary, the conclusion drawn is, (3) that 

 there is a struggle for existence, the deaths on the average 

 equalHng the births. Accepting the struggle for existence 



