BLENDING IMPLIES RETROGRESSION 197 



a blend, the offspring approach the ordinary specific type more 

 nearly than either parent ; that is, there is retrogression or 

 * regression ' as regards the progressive variations of both parents 

 a retrogression towards the specific mean. Again, suppose 

 there is exclusive inheritance, so that the peculiarity of one parent 

 is entirely lost. We noted that this very often happened in the 

 case of those numerous small redundancies, those small progressive 

 variations which offspring invariably display. 1 Here, again, there 

 is return to the specific type and retrogression. When offspring 

 inherit exclusively from the progressive parent, there is, of course, 

 no retrogression ; but this, as proved by the general tendency to 

 retrogression, happens comparatively infrequently, and, in any 

 case, there is no progression. 



324. Blended inheritance, therefore, nearly always implies 

 retrogression when parents differ. The characters in which they 

 differ tend to be lost, wholly or partially, within the limits of the 

 difference. It never implies progression. When progression 

 occurs, it is due, not to blending, not to the intermixture of 

 parental germ-plasms, but to that spontaneous variability which 

 is present in all forms of life, including parthenogenctic types. 

 Notwithstanding all that has been written on the subject, there is 

 absolutely no evidence that sex is ever a source of progressive 

 variations. Whenever we are able to trace its influence clearly, 

 blending (i.e. retrogression) is what we observe. It is true that 

 cross-breeding may reveal latent characters in a domestic species. 

 But this apparent progression is never real. Indeed, it frequently 

 implies retrogression. 2 Again, when varieties are crossed and 

 their constitution 'broken,' as it has been termed, the increased 

 variability which has been said to occur in descendants may well 

 be due to alteration, through retrogression, of that tendency to 

 vary only within narrow limits, which was imposed by Natural 

 Selection on both varieties after they became adapted to their 

 surroundings to a return to that condition of wider variability 

 which was imposed on them while they were becoming adapted. 

 Varietal crossing, however, is a rare phenomenon in nature. It is 

 one of the abnormalities which especially distinguish artificial 

 breeding. 



325. The function of sex, therefore, is to bring about 

 retrogression. But this retrogression does not occur at hap- 

 hazard. On the contrary, sex, a principal source of retrogression, 

 does its work with as much discrimination as Natural Selection, 



l See 194. a See 189. 



