112 THE WORLD OF LIFE 



tliis law that very extreme developments, whether of body or 

 of mind — gigantic stature or supreme genius — are rarely 

 transmitted to the next generation. But if this special su- 

 periority has already persisted in the family for several gen- 

 erations, and both parents belong to this same superior stock, 

 then the reversion towards mediocrity is less marked, and the 

 special quality will almost certainly be transmitted, sometimes 

 even in still larger degree, to some members of the family. 



It is by acting on this principle that breeders of animals or 

 j^lants for special purposes are able to improve the race. In 

 each generation they choose the most perfect individuals, from 

 their point of view^, to be the parents of the next generation, re- 

 jecting or destroying all the inferior ones. It is in this way 

 that our race-horses, our best milking cows, our heavy-woolled 

 sheep, our quickly fattening pigs, our luscious pears and 

 peaches, and hundreds of others, have been produced. Just 

 in proportion as we have bred only from the best for a long 

 series of generations does the transmission of these qualities 

 become more certain and the '' recession tow^ards mediocrity " 

 appear to be abolished. But it is not really abolished. The 

 average to w^hich there is a tendency to return has itself been 

 raised by careful selection of the best for many generations, 

 and the inferior individuals which were once the average of 

 the race are now so far removed that they can exert only a 

 very slight influence on each successive generation. Owing to 

 the numerical law above referred to, after five generations of 

 such selective breeding it is about 100 to 1 against the inferior 

 characters of the original average stock reappearing in the 

 offspring, while if the operation has been carried on for ten 

 generations it is about 2000 to 1 against such inferior types 

 presenting themselves. It is for this reason that our great 

 Colonial sheep and cattle breeders find it to their advantage 

 to give even thousands of pounds for pedigree bulls or rams 

 in order to improve their stocks. 



It is by what is substantially the same process, as wt shall 

 see farther on, that nature works to improve her stocks in the 



