

io8 NATURAL SELECTION AND 



whose domestic arithmetic was always accurate ; 

 and the people who believed that two and two 

 made five, whether on this planet or on that 

 other feigned by John Stuart Mill, would be 

 at a disadvantage in fighting with the people 

 who had established the doctrine that two and 

 two made four. Plato says that Agamemnon, 

 would have been a poor sort of general if he 

 had not been able to count his own feet ; 

 and Mr. Wallace himself admits the military 

 advantage possessed by the Romans in their 

 engineering skill. An Archimedes, though per- 

 haps less useful as a heavy-armed soldier than 

 a stupider man, was certainly of service to his 

 fellow-citizens in the carrying on of war. 



Elementary arithmetic and elementary per- 

 ceptions of spatial relations would undoubtedly 

 be useful to men living even under the rudest 

 conditions, and the brains capable of very 

 simple mathematical thinking may well enough 

 be the ancestors of brains capable of more 

 complex processes, if the capacity has been 

 accumulated by favourable combinations of 

 parents occurring again and again. It is not 

 difficult to account for the fact that mathe- 

 matical genius of a high order is sporadic, and 



