Table 1.
A comparative overview of evolutionary hypotheses on the fertility transition. Theoretical approaches are organized into three different phases: the origins, spread and maintenance of low fertility.
| Evolutionary Hypothesis | Low fertility adaptive? | Level of analysis | Psychological mechanisms | Causal model | What's different about market economies? | Key publications | |
|---|---|---|---|---|---|---|---|
| ORIGINS | Adaptive lag | no | individual | Natural selection has not shaped psychologies to optimize family size | Sex and reproduction are decoupled; selection pressure low | Modern contraception | Laland & Brown [22] |
| Embodied capital maximisationa | no | individual | Parents invest in skills and knowledge acquisition | Energetics of reproduction decoupled from resource and skill accumulation; QQTO | Wage-labour markets require embodied capital, investment potentially unlimited | Kaplan [10]; Kaplan et al. [24]; Grafen [42] | |
| Coevolution of wealth inheritance and fertilitya | no | individual | Parents invest in wealth or status accumulation | Wealth inheritance affects ability to marry and reproduce; QQTO | Unlimited opportunities for wealth creation, status competition | Mace [7,43,44] | |
| Stabilizing-/lineage- selection on long-term reproductive success | yes | lineage | Status striving; avoid lineage extinction | Intermediate clutch sizes maximize fitness of next generation or avoid lineage extinction | Social stratification; wealth inheritance; competition between lineages | Low et al. [45]; Mueller [46]; Kaplan et al. [24]; Hill & Kern-Reeve [47]; Boone & Kessler [48] | |
| Social mobility strategy | yes | family | Parents invest in wealth or status accumulation | Differential marginal reproductive returns to up- or downward mobility | Social stratification; Reproductive failure at the bottom of the hierarchy | Rogers [49]; Harpending & Rogers [50]; Rogers [51] | |
| Variance or risk compensation | yes | individual | Parents invest in wealth or status accumulation | Over-reproduce when uncertainty is high, under-reproduce when low | Mortality decline | Winterhalder & Leslie [52]; Leslie & Winterhalder [53]; Low et al.[54] | |
| Cultural versus biological 'parentage' | no | individual | Individuals invest in own wealth or status accumulation | Reduce fertility to maintain or obtain prestige position | Stiff competition for prestige-positions | Richerson & Boyd [55]; Boyd & Richerson [21] | |
| Loss of kin influence | no | individual (or group) | Teaching bias; give pronatal advice to kin | Loss of kin in social networks reduces their potential impact on reproductive norms | Social networks widen and become more diffuse | Newson et al. [56,57] | |
| SPREAD | Cultural niche construction | no | group | Frequency-dependent bias; Conformity bias | Distribution of cultural trait 1 alters percolation of cultural trait 2 via horizontal/oblique transmission | Mass education, communication networks, social networks widen | Cavalli-Sforza & Feldman [20]; Ihara & Feldman [58]; Kendal et al. [59]; Borenstein et al. [60]; Fogarty et al. [61] |
| Prestige- / success- biased transmission | no | individual | Prestige- or success-biased copying | One-to-many transmission, small 'effective' population size of traits; cultural 'drift' | High status people have sacrificed fertility to keep their prestige-positions | Richerson & Boyd [35]; Henrich & Gil-White [62] | |
| Cultural group selection | individual no; group yes | group | Frequency-dependent bias; Conformity bias; Selective migration; Prestige-bias | Competition between groups for development, resources, immigrants | Globally interconnected networks of mutual investment and competition | Richerson et al. [63]; Richerson & Boyd [64]; Dang [65]; Dang & Bauch [66]; Henrich [67] | |
| MAINTENANCE | Cultural evolutionary population dynamics | no | group | Cultural innovation; vertical and horizontal transmission of preferences and lifestyles; frequency-dependent bias | Lifestyle innovation is faster than natural selection on low fertility | Lifestyle innovation is faster, mass communication | Kolk et al. [68]; Ghirlanda & Enquist [69]; Ghirlanda et al. [70] |
aThese hypotheses also make partial use of the logic of adaptive lag, in that they argue the strategy was adaptive in the past, even though the reproductive outcomes today may not maximise fitness (QQTO: quality–quantity trade-off).