EVOLUTION AND MANKIND. 299 



individuals better adapted to secure such necessary ccmditiL^ns as 

 food, air, water, sunlight and ground space survived longer and 

 left more progeny than their less fortunate relatives. Doubtless 

 the total effect of this internal struggle among the individuals of 

 -ix species may be to raise the general level of the si)ecies" capacity 

 and to allow one species to encroach upon the ground of another. 

 Examples of this might be cited, such as the supplanting of the 

 Australian carnivorous marsupial, the Thylacine, by the dingo, a 

 tru-^ dog. The success of the latter is probably due to its being 

 hardier, possessing a relatively larger brain and Iveing more 

 adaptable to its environment. Darwin referred to the brown and 

 the black rat in connection with the struggle for existence. The 

 brown or Norway rat, Mus dccuuvanus, is an outdoor animal, a 

 burrower, keeping mostly to the ground. It may haimt sewers 

 and drains and is a scavenger. The black rat, Mtts rattus, on 

 the contrary, is more active, it has a longer body and can climb. 

 and in the East, it nests in trees or on housetops. It feeds on 

 grain, but is more shy than the brown rat. The Alexandrine rat 

 is the golden-brown variety oi the black rat. The story in the 

 popular books regarding the brown rat attacking and ousting the 

 black rat is not correct, for in the port of London the black rat 

 is increasing in numbers, as also in various suitable parts of 

 Europe. 



Another interesting example oif the struggle for existence 

 but of a different kind, may be considered. It is the relation of 

 a parasite to its host. It is not to the advantage of a para- 

 site to kill its host. Parasites which are frequently fatal ro. 

 their hosts, such as Tryp-anosoma rhodcsicnse, the causal agent 

 of Rhodesian sleeping sickness, are considered recent intruders, 

 that is. new parasites to their hosts. Parasite and host after a 

 time tend towards a mutual tolerance of each other. 



Analogies have been drawn between nations and communi- 

 ties of social insects, such as ants, bees, wasps and termites (white 

 ants). Such insect communities are really families, often pro- 

 duced ifrom a single pair. As Chalmers Mitchell writes : 



Their habits and customs have been described vi'ith a wealth of 

 picturesque language and an attribution of human motive excessive 

 even for writers on natural history, and I suspect that much new observa- 

 tion and careful interpretation arc required before we can really under- 

 stand what is going on. 



Without discussing details, for which there is not time, it must 

 be pointed out that in comparing insects with men the analogy is 

 vitiated, because of their great difference in mental constitution. 

 Social insects may represent the highest stage of instinctive action,. 

 man the highest development of conscious intelligent action. 



I cannot do better than to conclude this argument by quoting 

 at length from Dr. Chalmers Mitchell : — 



The strength and ferocity so frequently displayed in the animal 

 Icingdom, the restless pursuit of their prey by hungry animals, the use 

 of offensive weapons such as beaks and claws, Jiorns and teeth, are 

 frequently used as analogies for the activities and weapons of human 

 warfare. But the comparison does not bear close examination. The 



