When husbands are somewhat older than wives (but neither much older nor much younger), selective fitness is high, as operationalized by rates of short-term infant survival and neonatal breastfeeding

Pelham, B. W. (2021). The husband-older age gap in marriage is associated with selective fitness. Journal of Personality and Social Psychology, Jan 20201. https://doi.org/10.1037/pspi0000319

h/t David Schmitt "When husbands somewhat older than wives (but neither much older nor much younger)...8 cross-cultural replications w/ 225,000 mothers in low- to moderate-income nations...revealed husband-older age gap & life history tradeoff in lifetime selective fitness

Abstract: Wives are usually younger than their husbands. Although this has been replicated across time and culture, there is no previous evidence of the likely evolutionary underpinnings of this age gap. Study Set 1 replicated the marriage age gap—and its moderators—in 6.4 million American marriages that led to U.S. births between 2016 and 2018. This effect also replicated in three million unmarried unions. Study 2 directly examined the life history tradeoff that connects the marriage age gap to selective fitness. When husbands are somewhat older than wives (but neither much older nor much younger), selective fitness is high, as operationalized by rates of short-term infant survival and neonatal breastfeeding. This pattern held independent of the robust effects of maternal age. Eight cross-cultural replications involving more than 225,000 mothers in low- to moderate-income nations examined lifetime selective fitness (total number of living children) rather than single birth outcomes. In all eight nations, analyses revealed both a husband-older age gap and a life history tradeoff in lifetime selective fitness. Life history tradeoffs account well for the husband-older age gap in marriage.