138 RETROGRESSION 



differs in different species, but always bears a close relation to 

 the number of offspring which it is possible to rear. Plants and 

 low animals, whose characters are developed wholly or almost 

 wholly under the stimulus of nutriment, do not protect nor train 

 their young, which are able to fend for themselves from the first. 

 Therefore their offspring may number millions. The physical and 

 mental characters of the higher animals are developed largely 

 under the stimulus of use ; the individual is born more or less 

 helpless, and must be protected and trained during development. 

 Therefore the number of offspring that can be reared is very small 

 compared to that in the lower types. Everywhere we find an 

 adaptation as regards fertility which would have been impossible 

 unless individual peculiarities in fertility had been transmissible 

 and had thus afforded materials for Natural Selection. It is said 

 sometimes that, throughout nature, intelligence and fertility are in 

 inverse ratio to each other. This is true ; but not for the reason 

 alleged that they are fundamentally antagonistic to one another. 

 It is true only because intelligence has to be trained. 1 The greater 

 the intelligence achievable by an animal, the more helpless it is at 

 birth and the more prolonged and strenuous must be its preliminary 

 training by its parents. Therefore, since intelligent animals are 

 able to protect and train only a few offspring, parsimonious nature 

 has rigorously limited the number of the latter. In the case of 

 man, as proved in the laboratory and more massively by Registrar- 

 Generals and the officials that correspond to them in foreign countries, 

 there are considerable differences in fecundity in the number 

 of offspring actually produced as distinct from the number which 

 might be produced between races and classes. This may indicate 

 differences in fertility ; but before the question can be decided, we 

 must pass, as in the cases of ' ability ' and resisting power to disease, 

 outside the laboratory and inquire into a multitude of circumstances, 

 such as the customs of the people, average age at marriage, religion, 

 morality, sanitation and general health, physiological knowledge, 

 desire for large or small families, and the like. Unless these are 

 considered, every deduction concerning human fertility which 

 expands an induction that was reached through a statistical con- 

 sideration of fecundity is illegitimate. 



230. Numerous biometric studies of variability have been pub- 

 lished. In each case various characters in a number of individuals 

 (the more the better) of the same race have been measured and 

 the dimensions tabulated. In this way a very considerable 



1 See 624. 



