SUMMARY 437 



the specific mean. It follows also that the germ-plasm of every 

 species is less susceptible to the direct action of influences to which 

 it has long been subjected than to influences of which it has had 

 little or no previous experience. All, or nearly all, the variations 

 which furnish material for Natural Selection are fluctuations ; that 

 is, they are small plus or minus variations of characters previously 

 existing, and, even so, not of the whole character but only of parts or 

 qualities of it. By their accumulation and blending during ages, 

 old characters are lost and new characters created ; or, more 

 commonly, old characters are so modified as to be in effect new 

 creations. All development is an abbreviated and inaccurate re- 

 capitulation of the life-history of the species. Retrogression plays 

 as important a part in evolution as progression. Variations are 

 either progressive or retrogressive. Natural Selection has so dealt 

 with species that retrogressive variations tend to predominate 

 somewhat over progressive variations because they tend to be more 

 numerous, or larger, or prepotent in the blend, or on all these 

 accounts. As a consequence all characters tend to retrogress on 

 cessation of selection. Species fit their environments so closely, 

 and their physical and mental parts and qualities interlock so 

 exquisitely, that in nature mutations can rarely be adaptive. 

 Owing to their size, and to the alternative mode in which muta- 

 tions tend to be reproduced, they have an appearance, but only an 

 appearance, of great stability. When reproduction is bi-parental 

 and the species is sexually dimorphic, all individuals have three 

 sets of characters, a non-sexual set of characters all of which are 

 patent, and two sets of sexual characters of which one set is patent 

 and the other latent. The function of sex is to blend characters, 

 and the ultimate effect of blending, combined with the prepotency 

 of retrogressive variations, is to cause the retrogression of useless 

 variations and characters and to make evolution depend, not on 

 the persistence of the variations of individuals, but on the per- 

 sistence of the blended variations of the race as a whole. All bi- 

 parental inheritance is blended, the apparent non-blending of the 

 sexual and Mendelian characters being due to the fact that the 

 patent set from the one parent blends with the latent set from 

 the other. Natural Selection differs from Artificial Selection 

 in that the former is founded mainly on fluctuations, whereas the 

 latter is founded mainly on mutations. Mendelian reproduction is 

 an anomaly of sexual reproduction whereby non-sexual characters 

 are reproduced and blended in the same mode as sexual characters, 

 one of each allelomorphic pair being patent and the other latent. 



