VARIATIONS IN ANIMALS AND PLANTS 489 



intraspecific, that of individuals within the species. When members 

 of related species enter into competition in the same region, the 

 struggle becomes in a degree interspecific, one between the species them- 

 selves through their actual representatives. But as there is practically 

 no cooperation among members of the same species, except in the family 

 or band relation of the higher animals, the struggle must be in fact 

 always individual. The struggle against the environment in general is 

 in its essence non-competitive, but in the crowd of animals and plants 

 competition becomes part of the environment. Some seeds, we are told, 

 fell on stony ground, but the plants died because they had no depth of 

 earth. Some fell among thorns, and the thorns grew up and choked 

 them. Still others doubtless perished because they were planted too 

 close together. These three causes of the destruction of the great body 

 of animals and plants, the competition with like forms, that with unlike 

 forms, and the pressure of the environment, are present everywhere 

 with all life in varying degrees, and by it all life is forced into lines 

 of adaptation. 



With vital characters, selection preserves those which have no util- 

 ity by the simple action of heredity. All Southdown sheep have 

 tawny faces, although this trait bears no relation to the short firm 

 wool or to the fat and tender flesh, for which traits the Southdown 

 sheep are bred and valued. 



In similar fashion, many indifferent characters are traceable in the 

 various breeds and strains of domesticated animals and cultivated 

 plants. We may presume that similar characters in wild animals and 

 plants have been similarly carried along by inheritance from ancestors 

 possessing them. This phenomenon I have elsewhere called l the sur- 

 vival of the existing.' The actual traits are reproduced by heredity 

 without regard to any question of fitness. 



Dichromatism 



The phenomena of dichromatism belong to the category of indi- 

 vidual variation. In the vast majority of animals, we have the 

 dimorphism of sex. In the beginning the embryo is sexless. From the 

 beginning, by forces imperfectly understood, its development must be 

 directed in one way or another. It must assume the structures and 

 functions of one or the other sex. With certain insects, a polymorphic 

 condition exists. With bees, the caste of workers or atrophic females 

 exists, together with the type of drone and queen. With some ants, 

 still other types of individuals occur, but the dimorphism of sex, or 

 the polymorphism of the division of labor, rests on influences perhaps 

 not altogether inherent in the structure of the parent cell. 



In dichromatism, the individual from the first shows one or another 

 of two color patterns peculiar to the species. The screech owls are some 

 gray, some rusty red, within the same species, even in the same nest. 



