NECESSARY TRUTHS 137 



a lower type, and that the offspring of human beings are also 

 human ; that is to say, that human beings tend to reproduce 

 parental characteristics. It is likewise a patent truth that 

 man has more intellectual ' ability ' than any lower animal, 

 and another that some human races, those that have suffered most, 

 are more resistant to disease than others. At least, all these truths, 

 however ignored in the laboratory, are universally believed. Again, 

 it is a patent truth that a species or race is merely an aggregate of 

 related individuals, whence it follows that if one generation of a 

 species or race tends to transmit its characters to the next, then 

 individuals must tend to transmit their characters also. Conse- 

 quently it is inconceivable that human ability and powers of 

 resisting disease can have been evolved unless the paternal 

 characteristics, including variations, in these respects tended to be 

 inherited. Given the evolution, the general tendency to inherit 

 degrees of capacity is a necessary corollary which hardly needs 

 biometric confirmation. Here, as always, we create much better 

 science when we deduce one truth as a necessary corollary from 

 another (i.e. when we link the two truths together by a chain of 

 causation) than when we state them separately as isolated facts or 

 hypotheses. 1 This unnecessary isolation of hypotheses is a principal 

 feature and fault of nearly all laboratory work. Science describes 

 nature ; and nature is a unity in which nothing is isolated. More- 

 over we have no means of estimating the ability of individuals 

 except by noting the degree of intelligence observable, and, as we 

 shall see later, intelligence depends largely on mental training, on 

 education, which differs greatly in different classes and races and 

 cannot be estimated in the laboratory. We have no means of 

 estimating resisting power to disease except by observing the degree 

 of resistance displayed under conditions of food, general health, 

 intensity of exposure to disease, and the like, all of which may vary 

 with time and place and are also outside the range of the 

 laboratory. 



229. Similarly biometricians have sought to demonstrate that 

 individual degrees of fertility in men and horses tend to be 

 transmissible. But how, unless we presuppose some recent and 

 extraordinary change in nature, is the contrary conceivable ? 

 Manifestly the relative fertility of species (groups of related 

 individuals) is an adaptation, a product of evolution, which could 

 not have arisen unless the variations, the peculiarities, of individuals 

 had tended to be inherited by offspring. The degree of fertility 

 1 See 75 (footnote), 352 (footnote). 



