FECUNDAL AND INSTITUTIONAL SELECTION. 207 



Another result from the combined action of these two laws is that, 

 in species well adjusted to the environment, the typical, that is the average, 

 form of the species is not only the best adapted, hut it is the most fertile; 

 and this correlation between fertility and adaptation in the average 

 form of the species or race is a strongly conservative principle, tending 

 to prevent the rapid transformation of the race or species. Giants, 

 dwarfs, and extreme departures from the type of other kinds are more 

 likely to be sterile than the typical form of the species ; and therefore 

 if, through change in the environment or in the social conditions, some 

 extreme form has an advantage in gaining subsistence, it will usually 

 fail of propagating its kind with the relative rapidity of the less-favored 

 average form. This is at present true of highly intellectual variations 

 of civilized man. Those of moderate capacities are more prolific and 

 accordingly persist, though less successful in other respects than the 

 intellectual. But so long as the most successful individuals are those 

 surpassing the average in intellectual endowment, so long will the aver- 

 age endowment be more or less steadily advancing ; for, of intellectual 

 families, those that are fairly fertile will leave more impress on succeed- 

 ing generations than those that are sterile; and of fertile families, those 

 that are above the average in intellect will have the advantage in leav- 

 ing descendants to inherit their endowments. 



(16) Institutional selection is a form of exclusive breeding closely re- 

 lated to social selection, but differing from it very much as artificial 

 selection differs from natural selection. Institutional selection is 

 the influence of institutions, customs, and laws in determining what 

 classes of individuals have an opportunity to raise children. In most 

 civilized countries criminals convicted of important offenses are 

 usually so confined as to prevent their adding to the population of the 

 community during the time of their confinement. This is a method 

 of improving the race that might be carried farther than it has been. 

 In some countries the insane, the imbecile, and lepers are confined in 

 asylums and not allowed to marry, and in other countries eccle- 

 siastical and military restrictions prevent certain portions of the 

 community from raising families. 



(17) * Pradential selection is due to the delay of marriage and other methods 

 of limiting the number of children for prudential reasons. 



(18) Result of the foregoing survey of selectional intension. — The analy- 

 sis we have now completed shows us that certain changes in the form 

 of selection are due to changes in the environment and that others are 



*As section (17) does not occur in the original paper, it is printed in different 

 form. 



