An age-dependent ovulatory strategy explains the evolution of dizygotic twinning in humans

Abstract

An agedependent ovulatory strategy explains the evolution of dizygotic twinning in humans, Nature Ecology and Evolution 2020. DOI to be finalized. This function estimates lifetime reproduction in a cohort of women by simulating ovulatory cycles that can result in successful live singleton or twin births depending on inputs controlling prenatal and postnatal mortality, probabilities of single or double ovulation, maternal mortality both during child birth and independent of childbirth. It allows for up to 20 parities, makes an object that is a list of seven objects that can be further analysed and saves that object in the working directory as an .Rda file for future use. A set of input variables needed by the function, based on data from Gambia is provided by the function "prepGambiaBasic".

Mothers with higher twinning propensity had lower fertility in pre-industrial Europe

“…As for the other life-history traits, we quantified the effect of maternal age on the per-birth twinning probability while controlling for parity since both variables are strongly correlated (Spearman’s rho = 0.69 in our dataset) and potentially associated with twinning 1 . The GLMM fitted to our data is consistent with S1: we replicated the well-established result that the maximal per-birth twinning probability is reached when mothers were in their mid to late thirties 11 (Fig. 4c ; Supplementary Table 6 ).…”

“…2 raises a new question: how does the negative relationship between per-birth twinning probability and total births come about? One possibility is that maternal age, which we explicitly did not control for in the previous analysis, drives the relationship due to its influence on the per-birth probability of twinning 1 , 11 . For example, mothers that start reproducing from the age of 30 onwards show an increased probability of twinning but will have a short reproductive lifespan and few total births.…”

“…Building on the knowledge of human life histories, and the effects of maternal age and parity on human twinning in particular 1 , 5 , 9 , 11 , 20 , 23 , 38 , 39 , we hypothesised four non-mutually exclusive mechanisms that might shape the relationship between per-birth twinning probability and total births (Fig. 3 ).…”

“…Human twin births are rare but ubiquitous 1 , 2 . Despite a substantial research effort, evolutionary biologists 3 – 11 , as well as developmental biologists 12 , and geneticists 13 , 14 , continue to struggle to understand why twinning occurs and what influences its prevalence. Twinning also represents a practical challenge for public health since, even in the presence of high-quality medical care, twin births increase hospital costs and mortality rates for both mothers and offspring across populations 15 – 18 .…”

The 2021 Congress of the International Society for Twin Studies: Twin Research at the Cutting Edge/Twin Research: Maternal Bonding with Twins; Twins with Peters Anomaly; Selective Termination in Dichorionic Twin Pairs; Neuropsychological Function in Twins with Neurofibromatosis/News Reports: World’s Most Premature Survivor — A Twin; Twins Confuse Giants’ Baseball Fans; Malaysian Twins Switched at Birth; ‘Biracial’ Twins

“…(3) Dr David Anderson suggested the 'insurance ova hypothesis', namely that DZ twinning may represent an insurance mechanism compensating for chromosomal defects (Anderson, 1990). ( 4) Recent empirical work has supported Anderson's insurance hypothesis in humans (Hazel et al, 2020). ( 5) MZ twinning is a puzzling phenomenonbut it is not just a developmental accident.…”