488 POPULAR SCIENCE MONTHLY. 



the distinctions between genera are maintained. Consequently, 

 the progress of evolution is not a smooth and uniform progression, 

 but one that proceeds by jerks, through successive " sports " (as 

 they are called), some of them implying considerable organic 

 changes, and each in its turn being favored by natural selection. 



Galton's explanation of this specific stability is as follows: 

 The child inherits in part from the parents, in part from more 

 remote ancestors ; and since the sum of its ancestry, or, as Galton 

 terms it, the mid-parentage, is on the average nearer than the ex- 

 ceptional parents to the mean of the race, the children of selected 

 parents are on the average more mediocre than their parents. 



I have tried to show that, while the child is descended from a 

 long line of ancestors, it inherits from none but the two parents, 

 and that it can only be said in a figurative sense to inherit from 

 more remote ancestors. I shall soon refer to proofs that the per- 

 sistency of inherited types is due to natural selection, and not to 

 any principle of organic stability independent of selection. 



If this is true, if the stability of specific types is due to the 

 survival of the fittest, why do we have a type and not a fixed 

 standard ? If speed and strength and courage are good things, 

 why is not every individual as swift as the swiftest, as brave as 

 the bravest, and as strong as the strongest ? Why does not every 

 individual have every useful quality developed to the highest 

 excellence to which it may attain in any individual of the spe- 

 cies ? Why should we find that diversity among individuals 

 which usually passes under the name of " variation " ? 



We can measure strength and can treat it abstractly, and we 

 can artificially select and breed from the strongest members of a 

 stock, neglecting all other features; but this is not what takes 

 place in Nature. 



Here the most favored individuals are not the strongest, but 

 the ones in which all the qualities of the species are most per- 

 fectly co-ordinated with each other in relation to the external 

 world. Excessive strength may involve deficiency in some other 

 essential, and the mean or average strength of the species is that 

 degree of strength which is most in harmony with the mean de- 

 gree of development of all the other characteristics of the species ; 

 and the individuals who depart too widely from this mean, either 

 through excess of strength or deficient strength, are the ones 

 which are exterminated. 



Galton has himself given such a clear statement of the way a 

 type is established by selection that it can not be improved upon, 

 and I quote it in his own words : 



"Suppose," he says, "that we are considering the stature of 

 some animal that is liable to be hunted by certain beasts of prey 

 in a particular country. So far as he is big of his kind, he would 



