128 SPECIES. 



varieties would result among plants from the influence of the 

 physical medium, we must add to the notion of this medium, 

 as regards animals, the nervous activity of the ancestors. 



By the side of this creating influence we must recognise in 

 the medium a parallel destructive influence. Now, we can 

 appreciate this every day. The present tells us about the 

 past ; we cannot doubt but that species formerly disappeared 

 exactly as we see them still disappear under our eyes by the 

 manifestation of some new condition of the medium; these 

 may be sudden; volcanic phenomena, floods, extreme varia- 

 tions of temperature, diseases, famines, enemies all these 

 hypotheses are possible, and all equally reasonable : the dodo 

 has disappeared some years ago, having been destroyed by the 

 hand of man ; they say that the apterix will soon disappear in 

 the same way, devoured by cats. But actions only moderately 

 destructive were doubtless otherwise very important, and we 

 find here all the phenomena which have been so well described, 

 and so well explained by Darwin* under the name of vital com- 

 petition. By this we see, even since the most ancieni historic 

 periods, that certain savage animals, like the lion,f crocodile, J 

 and hippopotamus, || retire before mankind; that the black 

 rat is disappearing in Europe to give place to the field mouse, 

 and that a race of savages disappears when their country begins 

 to be inhabited by a more civilised race, even when the victors 

 in this organic, as well as political, struggle, are not able to 

 reproach themselves with any cruelty. 



Now, let us apply to man the theory of the origin of species 

 which we wish to be dominant, for there is no reason to think 

 that man forms any exception to the common rule. Before all 



* See On the Origin of Species, chap. iii. 



f Lions hindered the army of Xerxes in Macedonia. They abounded in 

 the province of Africa in the time of the Eoman Emperors. At the present 

 time, however, Gerard was obliged to watch for three hundred nights in order 

 to kill only thirty or forty. 



J The crocodile, which used to swarm on the Delta, is now only found in 

 Upper Egypt. 



|| The hippopotamus, since the Eoman occupation, has successively re- 

 tired from the mouth of the Nile to the fourth cataract. Some years ago, 

 there existed one, and one only, at the Island of Argo, on this side of New 

 Dongolah. Some hunters killed it, and since then, they have only been found 

 at the Berber level. 



