THE AGE AND AREA LAW 



441 



be its distribution in that country. It will be conceded by 

 most botanists that, as a rule, the species of Angiosperms are 

 not dying out, and, as the law of age and area applies only as 

 a fundamental, liable to be altered by a variety of causes in 

 particular instances, it follows that it applies, as a rule, to 

 Angiospermous species. It must be remembered that there 

 are numerous exceptions to the law of gravity and to most 

 other fundamental laws, and these are explained by modify- 

 ing causes. The law of gravity is not considered disproved 

 because a balloon or an aeroplane rises. 



By including a whole-hearted adherence to the theory of 

 the origin of species by mutation, an undue emphasis in his 

 first papers on the invalidity of natural selection as a cause 

 of the origin of species, and on the conclusion that endemic 

 species are, as a rule, younger than non-endemic species, Willis 

 has somewhat obscured the issue and brought upon his theory 

 the criticisms of natural selectionists and those who consider 

 endemic species to be as a rule relics of ancient floras. He 

 has also to face those ecologists who, by intensive study of 

 micro-species and their environment, seek to establish causal 

 relations between the concomitant circumstances of certain 

 modifications of environment and the distribution of these 

 micro-species. 



By a mass of statistics which are distasteful to the biological 

 mind, and which leave the biologist still sceptical and dis- 



D 



a 



b 



d 



f 



Fig. 1. 



h 



B 



trustful, Willis proves that practically all genera and all 

 families have the same type of distribution. It is, however, 

 unnecessary, except as the last stage of the proof, to put the 

 facts in a statistical form. If the area ABCD, fig. 1, be any 

 given region into which species arrive from outside regions 

 at AD, then the first group of species to arrive would have 

 29 



