title: 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.
authors.affiliation: School of Anthropology and Conservation, University of Kent, Canterbury CT27NR, UK Max Planck Institute for Demographic Research, Konrad-Zuse-Strasse 1, Rostock 18057, Germany ofb@kent.ac.uk.
authors.forename: Oskar
authors.initials: O
authors.lastname: Burger
authors.affiliation: School of Biological Sciences, University of Nebraska, Lincoln, Lincoln, NE, USA.
authors.forename: John P
authors.initials: JP
authors.lastname: DeLong
mesh_terms: D005075:Biological Evolution; D003710:Demography; D005298:Fertility; D006801:Humans; D012641:Selection, Genetic; D012922:Social Change; D012959:Socioeconomic Factors
keywords: demographic transition; evolutionary demography; fertility transition; resource constraints