Biology subjects

Young, E. A.

Publications and source records attributed to Young, E. A..

7 recordsLinked to original sources

bioRxiv2026

Mothers face immediate, but family-size dependent, costs of sons in preindustrial Finland

The expensive son hypothesis posits that mothers incur higher fitness costs when caring for sons versus daughters in species with male-biased size dimorphism. Evidence for maternal survival costs of sons in humans is limited to shortened overall lifespans; whether having more sons reduces short-term survival during reproductive years is unknown. Here, we utilised life-history data from 5,456 mothers from preindustrial Finland to examine whether mothers with more sons had reduced survival within one year of their last birth. While mothers with few children but more sons showed no differences in survival, at higher family sizes, mothers with more sons had increasingly lower survival. These differences peaked at [~]0.4% lower survival per son among mothers with five children, suggesting accumulated physiological costs of sons. These differences then declined and reversed among mothers with more children, potentially due to selective disappearance of frailer mothers. Our results suggest that studies focusing on post-menopausal mothers may bias estimates of the fitness costs of sons and reproductive costs more broadly. We recommend future research further examines the overlooked short-term fitness costs of sons during reproductive years, which is vital for understanding how life-history trade-offs, sexual dimorphism, and their interaction have shaped human evolution.

evolutionary biology↗

bioRxiv2026

Nucleotide diversity is a poor predictor of short-term adaptive potential

Significance statementThe current paradigm in conservation genetics suggests that species with the lowest molecular genetic diversity have the lowest capacity to adapt. Despite previous concern that traditional measures of molecular genetic variation are not useful predictors of adaptive potential, the conflation of genetic diversity and adaptive potential remains prevalent in both scientific literature and global policy. By combining new theory with a large dataset of genetic variation across hundreds of species, we show that molecular sequence variation is weakly related to the level of heritable variation in traits across species. This demonstrates that genetic diversity does not reliably predict adaptive potential, and highlights the urgent need to move beyond simple measures when assessing the evolutionary resilience of populations. A capacity to adapt is essential for a population to avoid extinction in a changing world and is recognised as a global conservation priority. Adaptation requires additive (heritable) genetic variation for traits that influence survival and fecundity, but measuring this variation is difficult, particularly in species of conservation concern. Instead, molecular genetic diversity is often used to infer adaptive potential. However, previous research has cast doubt on the suitability of traditional molecular markers (allozymes and microsatellites) for this purpose given their weak relationship with heritability - a common measure of additive genetic variance. Recent advances in sequencing technology have since shifted focus towards nucleotide diversity and variation in functional regions, but their practicality for predicting adaptive potential remains debated and untested. Furthermore, heritability itself is a poor proxy for adaptive potential because it depends on environmental variance. We collated 2,113 published estimates of evolvability - a measure of additive genetic variance that avoids environmental confounding - across 193 eukaryotic species, and evaluated how well evolvability is predicted by molecular diversity. We find that microsatellite and nucleotide diversity are not significantly correlated to each other, and neither predict evolvability (nucleotide diversity explains 0.7% of interspecific differences in evolvability and doubling nucleotide diversity only corresponds to a 9.2% increase in evolvability). With new theoretical work, we show that such weak associations are expected. Together, our results suggest that simple molecular measures of genetic variation are insufficient for predicting adaptive potential and continued reliance on these metrics risks misinforming conservation management.

evolutionary biology↗

bioRxiv2025

Life-history traits as predictors of expected genetic contributions 15 years later in a cooperatively breeding bird

An individuals life history plays an important role in how successful individuals are in passing on their genes to future generations. However, exactly which life-history traits best approximate an individuals long-term genetic contributions remains poorly studied, especially in cooperative breeders. Here, we use a genetic pedigree and long-term data of the closed population of the Seychelles warbler (Acrocephalus sechellensis) to calculate the expected individual genetic contributions (IGC) after 15 years (or [~]3 generations) across 11 cohorts. Using a Bayesian analysis we then quantified and compared how well six important life-history traits predict IGC in each sex of this cooperatively breeding species. The life-history traits compared were: acquisition of a dominant breeding position, age at first breeding attempt, tenure as a dominant breeder, lifespan, and LRS (measured as both the number of independent [surviving 3 months+] and recruited [surviving 1 year+] offspring produced over an individuals lifetime). An individuals lifetime reproductive success (LRS) was the strongest predictor of IGC and this predictive power did not differ across the different measurements used. However, this predictive power did differ between sexes, explaining [~]61-62% of IGC variation in males versus [~]47-49% in females owing to the larger variation among males in their annual reproductive success. Across other life-history traits the predictive power of IGC was similar across both sexes but differed between life-history traits considerably (2-37%). Comparing these predictive powers suggested that lifespan and the duration of a dominant breeding position are far more important in shaping long-term genetic contributions than if and when in their life they acquired dominance. Overall, these findings give insight into the individual and population-level processes influencing future gene pools and illustrate how life-history evolution is shaped by sex-specific reproductive patterns and cooperative breeding dynamics.

evolutionary biology↗

bioRxiv2025

Age- and sex-dependent sibling effects on early-life survival in preindustrial humans

Siblings are an important part of an individuals early-life environment and may therefore play an important role in shaping an individuals fitness. The quantification of sibling effects is challenging, especially in long-lived species with extended parental care and overlapping generations, such as humans. Here we quantify how the survival status, age, and sex of older siblings shape childhood survival across 2941 focal individuals born between 1750-1870 using historical parish data from Switzerland. While the total number of older siblings was not associated with an individuals childhood survival, distinguishing between siblings by their survival status, age, and sex revealed several associations, which in some cases also interacted with the sex of the focal individual: While older brothers close in age reduced the survival of girls but not boys, having more older sisters born close in age improved their younger siblings survival. Our results, therefore, show that sibling interactions play an important role in shaping early-life survival, and highlight that the strength and direction of these effects are context-dependent and can arise through biological and cultural factors. We encourage future studies on sibling interaction to consider siblings survival, age and sex, in both humans and other species.

evolutionary biology↗

bioRxiv2025

Genetic variation in life-history traits is not correlated with estrogen-receptor positive breast cancer risk

Estrogen receptor-positive breast cancer (ER+ BC) is one of the most prevalent cancers, but the evolutionary processes shaping genetic variation in ER+ BC risk are poorly understood. Both evolutionary life-history theory and evidence from studies of individual ER+ BC risk variants suggest that increased genetic ER+ BC risk is associated with faster maturation, earlier reproduction, and/or increased reproductive success (i.e., there is a trade-off), but it is unclear how well this pattern is replicated when considering the polygenic architecture of these traits after controlling for potential biases. Here, we estimate genome-wide genetic correlations between ER+ BC risk and three reproductive traits (age at menarche, age at first birth, and the number of children) using genomic restricted maximum-likelihood analyses on Lifelines biobank data and linkage disequilibrium score regressions on population and family-based genome-wide association study data. Regardless of the data or method used, genetic correlations were low and not statistically significant. Further analyses decomposing genome-wide genetic variance into local regions detected only three loci exhibiting significant pleiotropy between ER+ BC risk and age at menarche, suggesting little shared genetic architecture between ER+ BC risk and reproductive traits. Thus, the role of life-history trade-offs in shaping ER+ BC risk in European populations appears, at most, small, and the evolutionary processes giving rise to this life-threatening disease remain unclear. Future studies could examine the impact of evolutionary mismatches in shaping ER+ BC risk, where conducting longitudinal studies on populations transitioning to reproductive patterns observed in contemporary European populations would be most useful.

evolutionary biology↗

bioRxiv2024

Lifespan costs of reproduction increase during the Great Finnish Famine

Evolutionary theory of aging predicts that women with increased reproductive effort live shorter lives, but evidence is inconsistent. These inconsistencies could be because environmental conditions influence how much a mothers life span is reduced when having more children, i.e. their life-span cost of reproduction. Using a structural equation measurement model, we compare how reproductive effort affects the life span of 4,684 women exposed across different life-stages, or not at all, to the Great Finnish Famine. We find that life span costs of reproduction became higher in mothers exposed to the famine during reproduction, and for these mothers amounted to lower life expectancy of [~]0.5 years per child. Conversely, reproduction did not shape the life spans of mothers not exposed to the famine, or exposed post-reproduction or during development. This natural experiment reveals how environmental adversity can influence reproductive costs, providing a biological explanation for previous inconsistent findings, while showing how reproductive behavior has shaped the evolution of aging in humans. TEASERMothers with more children had shorter lives during a famine, suggesting that harsh conditions increase costs of reproduction.

evolutionary biology↗

bioRxiv2022

Lifetime reproductive success is an imprecise but largely unbiased predictor of long-term genetic contribution in historical humans

An individuals lifetime reproductive success (LRS) measures its realised genetic contributions to the next generation, but how well does it predict these over longer periods? Here we use human genealogical data to estimate expected individual genetic contributions (IGC) and quantify the degree to which LRS, relative to other fitness proxies, predicts IGC over longer periods in natural populations. This allows an identification of the life-history stages that are most important in shaping variation in IGC. We use historical genealogical data from two non-isolated local populations in Switzerland to estimate the stabilised IGC for 2,230 individuals ~10 generations after they were born. We find that LRS explains 30% less variation in IGC than the best predictor of IGC, the number of grandoffspring. However, albeit less precise than the number of grandoffspring, we show that LRS does provide an unbiased prediction of IGC and overall predicts IGC better than lifespan and similarly when accounting for offspring survival to adulthood. Overall, our findings demonstrate the value of human genealogy data to evolutionary biology and showing that reproduction - more than lifespan or offspring survival - impacts the long-term genetic contributions of historic humans, even in a population with appreciable migration.

evolutionary biology↗