492 TRANSMISSION 



fertility that fixes type, unless its effects happen to be overcome 

 by some other form of selection ; that is to say, the type of 

 highest fertility will become most numerous, and will therefore 

 naturally determine the type of the race. 



It is evidently the lessened fertility on the part of extremes, 

 and the higher breeding powers of the mediocre individuals, 

 that in nature assist selection in holding the principle of pro- 

 gression in check, thus generally, but not always, preventing 

 the splitting up of races into smaller varieties ; indeed, type is 

 mainly the resultant of relative fertility and selection, very 

 largely of the former. This is why breeders of highly improved 

 races must needs look well to fertility, for at that point their 

 first troubles will arise, all regression tables indicating that they 

 will never suffer from lack of variability, as seen in the following 

 section. 



SECTION IX PROGRESSION. PARENTS IN GENERAL PRO- 

 DUCE A FEW INDIVIDUALS MORE EXTREME 

 THAN THE RACE 



What is true of averages is not necessarily true of individuals 

 or of selected groups. Regression applies to the mass, not to 

 the separate individuals that compose it. 1 



Parents in general produce individuals both inferior and 

 superior to themselves, forming a frequency distribution whose 

 mean lies somewhere between that of the parent and the general 

 mean of the race. But the individuals extend both ways from 

 this mean and some of them lie well beyond the range repre- 

 sented by the parentage. On this point see any row in any 

 regression table, as row e in the table of statures (page 480). 



For example, in the case at hand, but 5 mid-parents, and pos- 

 sibly only 4 (10 or 8 parents), are above the height 72.5 inches 

 (see row ), but 31 children are recorded at 73.2 or above (see 

 columns 14 and 15). The number of extreme children is thus 

 more than three times as great as the number of extreme 



1 For example, we have shown that, on the average, offspring are more mediocre 

 than their parents ; but for a highly selected offspring (72-inch stature) we should 

 find the parents to be nearer mediocrity than the offspring. 



