THE EXISTENCE OF SPECIES 



Organization through Interwoven Lines of Descent a Characteristic of Species- 

 Biology Not Advanced by Ignoring this Fundamental Condition — 

 Eugenics a Problem of Maintaining the Species, rather 

 than of Separating Varieties. 



O. F. Cook, 

 Bureau of Plant Industry, U. S. Department of Agriculture, Washington, D. C. 



THAT all the plants and animals 

 are organized into species is a 

 fundamental fact of biology. If 

 the organization of species were 

 confined to a few groups of plants or 

 animals it woiild have been considered 

 very remarkable and would have been 

 made the subject of special investiga- 

 tion. But being universal and altogether 

 familiar, the existence of species is 

 taken entirely for granted in some 

 branches of biology and as completely 

 disregarded in others. 



Darwin had deeper insight into the 

 problems of evolution and heredity than 

 many of his successors, because he saw 

 that these problems relate to species; 

 that is, to species in the sense of natural 

 groups of interbreeding organisms. Tax- 

 onomic complications regarding species 

 have been allowed to confuse the issues 

 to such an extent that current writers 

 on general biological problems leave the 

 phenomenon of specific organization 

 entirely out of account or even deny that 

 species have any real existence. A single 

 instance may serve to illustrate this 

 tendency : 



"We have devised a scheme whereby 

 we regard animals as segregated into a 

 series of groups — species, genera and so 

 on — subordinated one to another. We 

 arbitrarily separate these groups by sharp 

 lines. While the scheme expresses, to 

 some extent, our ideas concerning the past 

 history of animals, the groups themselves 

 have no real existence 'in nature,' as we 

 say. There these sharp lines do not exist. 

 The species or other group has no definite 

 limits in space, no form, no integrity. It 

 has no organization as a whole." 



Plants and animals can be investi- 

 gated in many ways without taking 



account of the organization of species. 

 The interwoven lines of descent that 

 bind the members of a species into a 

 coherent organization may be separated, 

 as in the breeding of varieties of our 

 domesticated plants and animals, and 

 endless experiments can be made with 

 such varieties without considering their 

 derivation from an ancestral specific 

 organization. Many investigators prefer 

 to study varieties rather than species 

 because varieties have more uniform 

 characters and more definite differences, 

 so that the results of experiments are 

 more readily reported in statistical form. 

 When this preference is taken into 

 account it is not surprising that theories 

 of heredity should have been based upon 

 facts drawn from the study of varieties, 

 without considering the organization of 

 the species. 



THE SPECIES IN EUGENICS. 



As long as our interest is limited to the 

 varieties that are brought into the gar- 

 den or the breeding pen for experimental 

 purposes, it may appear better policy to 

 avoid reference to species, but in the 

 study of eugenics this policy can hardly 

 be maintained, for eugenics does not 

 have the same purpose of develop- 

 ing specialized uniform varieties. The 

 problem of eugenics is to learn how to 

 improve the human species in other 

 ways, without destroying individual 

 diversity or the normal network of 

 descent. Human progress, to be perma- 

 nent and secure, must be made in normal 

 evolutionary ways, instead of by any 

 direct imitation of the method of pro- 

 ducing our short-lived varieties of 

 domesticated plants and animals. Hence 



155 



