56 DARWINISM AND THE PROBLEMS OF LIFE 



is no sharp distinction between a species and a 

 variety. 



This modern discovery has thoroughly shaken the 

 old Linnean principle : " There are as many species 

 as there were distinct forms created." We now know 

 that species are changeable, and have actually changed ; 

 that one species may be formed from another. The 

 question is often raised, in the form of an objection, 

 why no species has been changed within our experience ; 

 in fact, it is urged that history shows the forms of 

 animals and plants to be just the same as they were 

 6,000 years ago, since the ancient Egyptians depicted 

 lions and other animals just as we have them to-day. 

 The objection seems to have some strength, but we 

 know of several cases in which species have been 

 so much modified within the historical period that 

 they can no longer be crossed with their earlier 

 relatives. 



In the year 14 19 rabbits were introduced on the 

 isle of Porto Santo, near Madeira, and increased until 

 they became a plague of the country. But the de- 

 scendants have become very unlike their ancestors, 

 and differ from them in their peculiar colour, rat-like 

 shape, small size, nocturnal habits, and extraordinary 

 savageness. But the most remarkable point is that 

 they can no longer be crossed with the European 

 rabbit, and have, therefore, formed a new species in 

 this comparatively brief space of time.^ 



However, this was an exceptional case. The 



1 The facts are related by Ernst Haeckel, who gave the Porto Santo 

 rabbit the name of Lepus Huxhyi. 



