204 THE FUNCTION OF SEX 



ment. When considering Natural Selection, we are apt to think 

 of the progressive variations of the individual as passing unchanged 

 to his descendants. As a fact, apart from his variations, the 

 descendant is, so to speak, a composite photograph of ancestors 

 from which useless characters are, more or less, excluded. It is 

 largely because conjugation has planed away redundancies and 

 blended into a congruous whole much that enabled the survivors in 

 past generations to persist till they had offspring that the individual 

 is so closely adapted to the average environment of his race. 



336. Self-fertilization is not uncommon in plants, and it occurs 

 also amongst vegetative marine animals. Doubtless it has arisen 

 as a substitute for cross-fertilization, owing to the uncertain 

 occurrence of the latter amongst the individuals of stationary and 

 scattered types. The germ-cells of an individual differ amongst 

 themselves, but not, on the average, to the same extent as germ- 

 cells derived from different individuals. In self-fertilization, 

 therefore, the influence of conjugation, though still potent, is less 

 than in cross-fertilization. Presumably, however, it is sufficient 

 for the needs of the comparatively simple types among which 

 it is found. Parthenogenesis is comparatively rare, and occurs 

 as a rule among simple forms, the multiplication of which is very 

 rapid, and which thus provide very abundant materials for Natural 

 Selection. The theory that the function of sex is to bring about 

 the retrogression of useless characters by the blending of paren- 

 tal traits, therefore, accords well, not only with the facts of 

 bi-parental reproduction, but also with those of self-fertilization 

 and parthenogenesis. 



337. The problem of sex occupies at present a disproportionate 

 share of biological attention. The study of it, under the name of 

 Mendelism, is very fashionable. Nevertheless, from a practical 

 point of view, indeed from every point of view, it is of lesser im- 

 portance than many other biological problems. A complex and 

 difficult question, it cannot be solved except by examining it from 

 all points of view, by utilizing all the evidence available, and testing 

 our thinking carefully. It cannot be too often or too forcibly 

 reiterated that the only extensive body of evidence in our possession 

 relating to normal intra-varietal breeding and the crossing of natural 

 varieties is that drawn from human races. That evidence indicates 

 decisively that offspring blend parental characters. To restrict our 

 data to the scanty and imperfect material obtainable by crossing 

 domestic varieties for a few generations, and even then by observ- 

 ing only the inheritance of glaring parental differences, is to court 



