38 ANIMAL LIFE AND HUMAN PROGRESS 



food plant, that is to say are adapted to it, more or less closely, 

 though the amount of dependence of a caterpillar on a par- 

 ticular food plant varies a good deal in different species. 

 Often, however, closely allied species are attached to different 

 plants. Analogous cases might be cited of the Sphegidae, the 

 species of which are attached to particular species of other 

 insects, or spiders, which they store in various ways as food 

 for their grubs. 



It would be easy to multiply instances, especially from 

 insects, whose habits have been so closely studied, but those 

 I have given will suffice to illustrate the point I wish to raise. 

 In each of these cases, do not these nearly related forms of 

 animal life withdraw from competition with one another, 

 rather than enter into it ? 



In every instance the adaptation that we admire enables 

 the organism to occupy some new territory and thus to avoid 

 competition for food or shelter with its nearest relatives. I 

 submit that this aspect of the question has not been sufficiently 

 considered, and that too much stress has been laid upon the 

 competition alleged to take place between individuals of a 

 species and closely related forms. In this connection it is 

 necessary to remember that Darwin derived his conception 

 of the struggle for existence from Malthus, thus applying to 

 the rest of the animal kingdom an idea borrowed from a 

 student of human sociology. It is true that mankind, largely 

 in consequence of the dominion he has gained over the lower 

 animals, has entered into the fiercest competition with 

 own kind ; nation with nation, tribe with tribe, individual 

 with individual. But I am by no means clear that this 

 principle enters, to the extent attributed to it, into the polity 

 of the lower animals. And if it does not, Natural Selection 

 ceases to have the importance attributed to it by Darwin and 

 Wallace ; still less the omnipotence (Allmacht) claimed for 

 it by Weismann. 



To further illustrate this point, I will take the case of 

 Lamellibranchiate (Bivalve) molluscs. They are a very 

 ancient and a very successful group, in the sense that they 

 are numerous in individuals, wide-ranging, and abundant in 



