1036 LIFE : OUTLINES OF GENERAL BIOLOGY 



the Fair Island Field Mouse {A. fridariensis), which occurs on 

 Fair Isle, with a variety on Yell. Many would add a fifth British 

 species, the southern Yellow-Necked Field Mouse {A. flavicollis). 

 So the question is where the Foula mouse comes in, and the 

 answer that the experts have given is that it is a sub-species of 

 the Fair Island Field Mouse, and should be called A. fridariensis 

 thuleo. How very thrilling! 



But that is just what it is, for in these insular forms we have 

 plainly to do with species in the making, with what the impatient 

 anti-evolutionist is always demanding and never looking for. Just 

 as the Fair Isle field mouse, the Hebridean field mouse, and the St. 

 Kilda field mouse are derivable from the widespread common long- 

 tailed field mouse {Apodemus sylvaticus), so the Foula mouse is at 

 present — of course, a long present — diverging from the Fair Island 



Fig. 179. 



The Foula Mouse, Apodemus fridariensis thuleo, a variety or incipient species 

 which has recently arisen in the island of Foula from introduced specimens 

 of the Fair Isle mouse {Apodemus fridariensis), which had itself a similar 

 origin from the mainland long- tailed Field Mouse {Apodemus sylvaticus). 



Species. Charles Darwin said in regard to the ten or so different 

 species of giant tortoise on ten adjacent islands of the Galapagos 

 archipelago, that he felt himself "brought near to the very act of 

 creation", and the naturalist of to-day must say the same when he 

 looks at the "Hill Mice" of Foula. Evolution is certainly going on, 

 and for men as well as for mice. 



It is reasonable to ask whether the Foula mice have any salient 

 features. But the answer to this question is bound to be disap- 

 pointing, for the species of field mouse differ from one another in 

 minutiae — the straws from which the expert knows how the evolution 

 wind has been blowing. Species of mice do not have much in the 

 way of salient features; they differ mainly in the details of their 

 skull bones! Yet it may be noted that the Foula mouse has parti- 

 cularty large hind feet, white on their dorsal surface, and with 

 small sole pads. It is a sturdy mouse, but distinctly smaller than its 

 Fair Isle ancestor. The two agree exactly in colour, having dark 



