88 CORRELATED VARIATIONS. 



mer, it is much less. As, therefore, fertility is proved 

 to be inherited in man, and fecundity in the horse, it is 

 probable that both these characters are inherited in all 

 classes of life. 



The importance of this theory of Genetic Selection 

 will, perhaps, be better realised by quoting a concrete 

 case concerning man, this being the only one in which 

 statistics are at present available. Working on data con- 

 cerning 4000 families, principally of the Anglo-Saxon 

 race, and 1842 families of the Danish race, Professor 

 Pearson * determined that there is a sensible correla- 

 tion (about .18) between fertility and height in mothers 

 of daughters. Supposing genetic selection to have been 

 unchecked by natural selection, say for forty genera- 

 tions, the mean height of women would have been raised 

 about 3J inches. A factor which would alter stature 

 by about three inches in 1000 years is clearly capable 

 of producing very considerable results in the long 

 periods during which evolution may be supposed to have 

 been at work. The importance of the influence of 

 genetic selection in the case of man is also shown by the 

 fact that, as proved by these statistics, less than a quar- 

 ter of one generation, by reason of their fertility, pro- 

 duce more than half of the next generation. Correla- 

 tion between fertility and any mental or physical char- 

 acteristic must therefore work a progressive change. 

 For example, arguing from the class fertility statistics 

 which have been determined among the population of 

 Copenhagen, it is gathered that the artisan class pro- 

 duce a larger proportion of children than the profes- 

 sional classes, as their gross fertility is greater, and 

 *Proc. Roy. Soc., lix. p. 301, 1896. 



