386 ANNUAL EEPORT SMITHSONIAN INSTITUTION, 1915. 



becomes common property, views more reasonable and, I may add, 

 more humane, are likely to prevail. 



To all these great biological problems that modern society must 

 sooner or later face there are many aspects besides the obvious ones. 

 Infant mortality we are asked to lament without the slightest 

 thought of what the world would be like if the majority of these 

 infants Avere to survive. The decline in the birth rate in countries 

 already overpopulated is often deplored, and we are told that a 

 nation in which population is not rapidly increasing must be in a 

 decline. The slightest acquaintance with biology, or even schoolboy 

 natural history, shows that this inference may be entirely wrong, 

 and that before such a question can be decided in one way or the 

 other hosts of considerations must be taken into account. In normal 

 stable conditions population is stationary. The laity never appre- 

 ciates what is so clear to a biologist, that the last century and a 

 quarter corresponding with the great rise in population has been an 

 altogether exceptional period. To our species this period has been 

 w'hat its early years in Australia were to the rabbit. The exploita- 

 tion of energy capital of the earth in coal, development of the new 

 countries, and the consequent pouring of food into Europe, the 

 application of antiseptics, these are the things that have enabled 

 the human population to increase. I do not doubt that if popula- 

 tion Avere more evenly spread over the earth it might increase very 

 much more, but the essential fact is that under any stable conditions 

 a limit must be reached. A pair of wrens will bring off a dozen 

 young every year, but each year you Avill find the same number of 

 pairs in your garden. In England the limit beyond which under 

 present conditions of distribution increase of population is a source 

 of suffering rather than of happiness has been reached already. 

 Younger communities living in territories largely vacant are very 

 probably right in desiring and encouraging more population. In- 

 crease may, for some temporary reason, be essential to their pros- 

 perity. But those who live, as I do, among thousands of creatures 

 in a state of semistarvation will realize that too few is better than 

 too many, and will acknowledge the wisdom of Ecclesiasticus who 

 said, " Desire not a multitude of unprofitable children." 



But at least it is often urged that the decline in the birth rate of 

 the intelligent and successful sections of the population (I am speak- 

 ing of the older communities) is to be regretted. Even this can not 

 be granted Avithout qualification. As the biologist knows, differenti- 

 ation is indispensable to progress. If population Avere homogeneous 

 ciA'ilization Avould stop. In eA'ery army the officers must be com- 

 paratively few. Consequently, if the upper strata of the community 

 produce more children than Avill recruit their numbers some must fall 

 into the lower strata and increase the pressure there. Statisticians 



