What if fertility decline is not permanent? The need for an evolutionarily informed approach to understanding low fertility

Abstract

‘Demographic transition theory’ assumes that fertility decline is irreversible. This commonly held assumption is based on observations of recent and historical reductions in fertility that accompany modernization and declining mortality. The irreversibility assumption, however, is highly suspect from an evolutionary point of view, because demographic traits are at least partially influenced by genetics and are responsive to social and ecological conditions. Nonetheless, an inevitable shift from high mortality and fertility to low mortality and fertility is used as a guiding framework for projecting human population sizes into the future. This paper reviews some theoretical and empirical evidence suggesting that the assumption of irreversibility is ill-founded, at least without considerable development in theory that incorporates evolutionary and ecological processes. We offer general propositions for how fertility could increase in the future, including natural selection on high fertility variants, the difficulty of maintaining universal norms and preferences in a large, diverse and economically differentiated population, and the escalating resource demands of modernization.

The cultural evolution of fertility decline

“…One demographer has speculated that richer countries may end up with higher fertility than poorer ones in the future [ 113 ]. While many demographers are sceptical about a return to high fertility, since short-term baby booms in the recent past have not dampened the general trend towards low fertility, assuming that this will be a long-term equilibrium state without a strong theoretical grounding may be dubious [ 114 ]. HBEs might interpret bounce-back as a sign that the adaptive lag in human responses to our radically altered ecological niche is coming to an end, or that, as more people become wealthy and educated, the marginal advantages to investment in quality over quantity are declining, leading to relaxed reproductive competition and to higher fertility.…”

Life-history theory and climate change: resolving population and parental investment paradoxes

“…Our current results suggest that while both r- and K -selected strategies can lead to higher carbon emissions, future orientation may mitigate expected carbon emissions through lowering fertility and interacting with parental investment, particularly in the context of higher education. Nevertheless, evidence for fertility rate increases in countries with the highest levels of development [36] suggests more research is needed into how orientation, and evolutionary approaches in general, can explain global patterns of human LH [28]. Future orientation and related psychological processes (e.g.…”

Nicotinamide and Demographic and Disease transitions: Moderation is Best

“…200–220 It will be ironic if meat equity could have avoided such high global populations and high meat and cattle needs that are a major contributor to deforestation and ‘green-house’ gases through the use of fertilisers, water, and fossil fuels. Technological advances, often invoked to show that Malthus was wrong, could be temporary and ultimately cataclysmic fixes unless technology changes its biases towards optimal meat intake rather than more and more cereals delaying demographic transitions 221–226 (Figure 8).…”