No. 546] SHORTER ARTICLES AND DISCUSSION 375 



cause those individuals which do become well placed thrive. The 

 burden of starvation passes by a number of the individuals to 

 fall upon the others. In this way, the evil effects of a general 

 underfeeding, which is the necessary result of direct sustentative 

 selection, is avoided. In cases, then, where indirect sustentative 

 selection is operative, the reproductive rate is that which will 

 produce enough individuals to find many of the favored places 

 and withstand the non-sustentative causes of death. Where 

 direct sustentative selection might be theoretically expected, as 

 in the case of the large birds of pn-y. in regions where they are not 

 persecuted, the rigors of a possible struggle are avoided by low 

 reproductive rates. 



While the reproductive rate must be looked upon as a char- 

 acteristic which has its adaptations like other characteristics, it 

 has one peculiarity — its increase is always opposed by lethal se- 

 lection. The chances of life are reduced by reproducing inas- 

 much as more danger is entailed by the extra activities of court- 

 ship, and later, of the care of the young, since they reduce the 

 normal wariness of individual life. The species, therefore, al- 

 ways keeps the reproductive rate at the lowest point which will 

 suffice for the reproductive needs of the species. For this reason 

 alone we should expect the non-sustentative selection to be the 

 predominant kind. 



Gulick and Pearson have shown that there is a normal conflict 

 between natural selection and fecundal selection. Fecundal se- 

 lection is said by them to be constantly tending to increase the 

 reproductive ratio, while lethal selection asserts its power to re- 

 duce it, because the reproductive demands on the parents reduce 

 their chances of life by interference with their natural ability of 

 self-protection. This is quite true, but the analysis is incomplete, 

 for an increased number of progeny not only decreases the life 

 chances of the parents, but also of the young, by reducing their 

 endowment and care. 



A further reason for believing in the predominance of non- 

 sustentative selection is the fact that the species that have 

 evolved furthest are well known to be of low fecundity. Man, 

 himself, even where there is no artificial restraint, has one of the 

 smallest reproductive rates known. If sustentative selection had 

 been predominant, we should expect higher fecundities in these 

 highly evolved species than in the lower ones. 



The fundamental formula of Malthusianism, that the number 

 of individuals iu a species tends to increase in geometrical ratio, 



