Low Fertility in Evolutionary Perspective

Abstract

From an evolutionary point of view humans have been extremely successful. They now number about 5 billion and are increasing by some 80 million each year. A sizable proportion of humans view the explosive multiplication of their species as a global catastrophe that has helped to expand poverty to extinguish thousands of other species to pollute the air to waste resources and to create congestion. For many observers the current below-replacement fertility in the industrial countries is a blessing not a calamity. Since these countries are in a minority however their self-restraint with respect to fertility reduces global population growth only slightly. Instead it gives the industrial countries aging populations and international complications. While these costs are leading some governments to pursue or consider pronatalist programs they are hardly great enough to justify programs that will do much more than achieve zero growth. To evaluate the present below-replacement fertility of the industrial nations one must recall the millions of years when humans like other animals hunted and foraged. Under those conditions a rapid expansion of human numbers was suicidal because it would lead to environmental exhaustion tribal warfare and disease. In some animals population stabilization is achieved by very high mortality but in others including humans it is achieved by moderate fertility which fits the evolutionary niche that humans have carved for themselves-namely a reliance on culture and technology. This reliance has succeeded best when emphasis was placed on the training of offspring rather than the number of offspring. With agriculture man began to live by controlling rather than simply skimming his environment. The switch was so profound and sudden that normal feedback mechanisms restraining population growth became partially inoperable. By greatly expanding production in agriculture and in other sectors of the economy and by finally inventing scientific medicine industrialism lowered death rates dramatically with consequent unbridled population growth. Since an industrial system must invest ever more heavily in the training of the young it soon exerts a downward pressure on fertility. With full industrialism the family which has survived up to this point becomes a weak institution and the output of babies becomes inadequate to replace the population.