The Evidence for Evolution 



to believe, is the older group of the two, and that from which 

 the apes have sprung. It is supposed, then, that Madagascar 

 was separated from Africa before the ape had evolved. The 

 lemurs thenceforward were free from the competition of their 

 more highly developed relatives, and have branched out into a 

 great variety of types, while still remaining on a relatively low 

 plane of intelligence and specialisation. The distribution of the 

 Lemurs is shown in Fig. 13. 



In Dr. Alfred Russel Wallace's book on Island Life there 

 are set forth a great number of interesting facts on the subject 

 of the animal population of islands, and many striking inter- 

 pretations of these facts in the light of the Evolution theory. 

 Coral islands, and those caused by volcanic eruptions, are peopled 

 with inhabitants which have accidentally come thither by flight, 

 or have been brought, for example, on floating timber by ocean 

 currents. On the other hand, islands which represent separated 

 fragments of continents have usually a fauna of the same general 

 type as that of the continent of which they have formed a part. 

 But the actual species are frequently different, and if the separation 

 is of more ancient date, the differences are still more marked. 

 The fact of this divergence of an isolated animal population from 

 that from which it has originated is sufficiently striking, and 

 would remain an inexphcable problem, were we without an 

 Evolution theory. According to the Evolution hypothesis, how- 

 ever, the restricted and somewhat special environment favours 

 a modification of the original types with which the island was 

 provided, and a satisfactory explanation is offered. 



Finally, we may mention the evidence that has been gathered 

 from the study of embryology and development. It has been 

 stated, in a metaphor which is perhaps more clever than it is 

 exact, that every animal climbs up its own ancestral tree ; and 

 while it would be absurd to say, for instance, that a mammalian 

 embryo resembles successively a fish, an amphibian, and a reptile, 

 still many of the broad facts in the evolution of a race seem to 

 be repeated, in a more or less blurred and indistinct fashion, in 

 the development of the individual. Thus, for example, gill-slits 



