Testing the evolutionary basis of the Predictive Adaptive Response hypothesis in a preindustrial human population

Background and objectives: The thrifty phenotype hypothesis proposes that late-life metabolic diseases result from mismatch between early-life and adulthood nutrition. More recently, the predictive adaptive response (PAR) hypothesis has suggested that poor early-life environmental conditions induce metabolic changes which maximise health and fitness in similarly poor adult conditions, but reduce fitness if conditions later improve. Therefore later-life survival and reproduction should be maximised where environmental conditions during development and adulthood match, but few studies in humans have addressed the consequences of poor early conditions on fitness traits in varying later conditions. Methodology: We tested key evolutionary predictions of the PAR hypothesis using detailed longitudinal data with several environmental parameters from a natural fertility preindustrial human population, to investigate how combinations of early- and late-life environmental conditions affected annual probabilities of survival and reproduction. Results: We found no suggestion that fitness was maximised when developmental and later-life conditions matched, but rather poor environmental conditions during development or later life and their combination were associated with lower survival. Conclusions and implications: Our results are more consistent with predictions of ‘silver spoon’ models, whereby adverse early-life conditions are detrimental to later health and fitness across all environments. Future evolutionary research on understanding metabolic disease epidemiology should focus on determining whether adaptive prediction maximises infant survival where conditions match during development and immediately after birth, rather than drawing attention to the unlikely long-term fitness benefits of putative metabolic changes associated with poor early nutrition

Luonnonvalinnan vai kulttuurin tuotteita?

Ihminen (Homo sapiens sapiens L.) on laajalle levinneenä ja moneen sopeutuvana lajina melkeinpä minkä tahansa mittapuun mukaan yksi tämän hetken menestyneimmistä selkärankaisista. Ihmisen lisääntymisstrategioiden evolutiivinen ymmärtämisen luulisi siis saavan osakseen paljon huomiota – lisääntymisstrategialla tarkoitetaan niitä keinoja, joita soveltamalla yksilö saavuttaa tuottamiensa jälkeläisten määrän

Self sacrifice and kin psychology in war : threats to family predict decisions to volunteer for a women's paramilitary organization

The conditions that propel humans to make sacrifices for groups of unrelated, and often unknown, individualshas received considerable attention across scientific disciplines. Evolutionary explanations for this type of sa-crifice have focused on how men form strategic coalitions organized around kin networks and reciprocity whenfaced with out-group threats. Few studies, however, have analyzed how women respond to external threats.Using data from one of the largest female paramilitary organizations in history we show that women who havemore brothers, women whose husbands serve in the military and women without children are more likely tovolunteer. These results provide qualified support for the hypothesis that women are more likely to sacrifice fortheir country when members of their family are at risk. Overall, our analysis suggests that self-sacrifice andintense bonding with an imagined community of unknown individuals, such as the nation state, may arise out ofa suite of psychological adaptations designed to facilitate cooperation among kin (i.e. kin psychology). Theseresults can be interpreted within the framework of kin selection showing how individuals come to view un-related group members as family. They may also shed light on various theories of group alignment, such as‘identity fusion’–whereby individuals align their personal identity and interests with those of the group–and onour understanding of evolutionary adaptations that cause women to direct altruism toward in-groups.Peer reviewe

Reproductive cessation and post-reproductive lifespan in Asian elephants and pre-industrial humans

Conclusions: Our results show that the reproductive and survival patterns of Asian elephants differ from other long-lived animals exhibiting menopause, such as humans, and extreme longevity alone does not promote the evolution of menopause or post-reproductive lifespan, adding weight to the unusual kin-selected benefits suggested to favour such traits in humans and killer whales.</p

Natural Selection on Female Life-History Traits in Relation to Socio-Economic Class in Pre-Industrial Human Populations

Life-history theory predicts that resource scarcity constrains individual optimal reproductive strategies and shapes the evolution of life-history traits. In species where the inherited structure of social class may lead to consistent resource differences among family lines, between-class variation in resource availability should select for divergence in optimal reproductive strategies. Evaluating this prediction requires information on the phenotypic selection and quantitative genetics of life-history trait variation in relation to individual lifetime access to resources. Here, we show using path analysis how resource availability, measured as the wealth class of the family, affected the opportunity and intensity of phenotypic selection on the key life-history traits of women living in pre-industrial Finland during the 1800s and 1900s. We found the highest opportunity for total selection and the strongest selection on earlier age at first reproduction in women of the poorest wealth class, whereas selection favoured older age at reproductive cessation in mothers of the wealthier classes. We also found clear differences in female life-history traits across wealth classes: the poorest women had the lowest age-specific survival throughout their lives, they started reproduction later, delivered fewer offspring during their lifetime, ceased reproduction younger, had poorer offspring survival to adulthood and, hence, had lower fitness compared to the wealthier women. Our results show that the amount of wealth affected the selection pressure on female life-history in a pre-industrial human population

The Long-Term Success of Mandatory Vaccination Laws After Implementing the First Vaccination Campaign in 19th Century Rural Finland

In high-income countries, childhood infections are on the rise, a phenomenon attributed in part to persistent hesitancy toward vaccines. To combat vaccine hesitancy, several countries recently made vaccinating children mandatory, but the effect of such vaccination laws on vaccination coverage remains debated, and the long-term consequences are unknown. Here we quantified the consequences of vaccination laws on vaccination coverage, monitoring for a period of 63 years (1837-1899) rural Finland's first vaccination campaign against the highly lethal childhood infection smallpox. We found that annual vaccination campaigns were focused on children up to 1 year old and that their vaccination coverage was low and declined over time until the implementation of the vaccination law, which stopped the declining trend and was associated with an abrupt coverage increase, of 20%, to cover >80% of all children. Our results indicate that vaccination laws can have a long-term beneficial effect of increasing the vaccination coverage and will help public health practitioners to make informed decisions on how to act against vaccine hesitancy and optimize the impact of vaccination programs

Changes in Length of Grandparenthood in Finland 1790-1959

The importance of grandparents for their grandchildren is well-studied in several disciplines, and studies are now also addressing the potential effects of grandchildren on grandparental wellbeing. Any such effects are limited by the time grandparents share with their grandchildren. Changing child mortality rates, grandparental longevity, and childbearing patterns may have profoundly altered the length of grandparenthood across the demographic transition, but this has received little scientific attention. Using a genealogical dataset from Finland, we investigate changes in this shared time, from the late 18th to mid-20th century. We found the number of shared years between grandparents and grandchildren was low until roughly the onset of industrialisation in Finland, after which point shared time increased rapidly, from both the grandchild and grandparent perspectives. Understanding changing patterns in the opportunity for intergenerational transfers between grandparents and grandchildren has implications for several fields of study, including biology, demography, sociology, health studies, and economics

Child volunteers in a women’s paramilitary organization in World War II have accelerated reproductive schedules.

Understanding how conditions experienced during development affect reproductive timing is of considerable cross-disciplinary interest. Life-history theory predicts that organisms will accelerate reproduction when future survival is unsure. In humans, this can be triggered by early exposure to mortality. Previous studies, however, have been inconclusive due to several confounds that are also likely to affect reproduction. Here we take advantage of a natural experiment in which a population is temporarily divided by war to analyze how exposure to mortality affects reproduction. Using records of Finnish women in World War II, we find that young girls serving in a paramilitary organization wait less time to reproduce, have shorter inter-birth intervals, and have more children than their non-serving peers or sisters. These results support the hypothesis that exposure to elevated mortality rates during development can result in accelerated reproductive schedules and adds to our understanding of how participation in warfare affects women.Peer reviewe

Nearby grandmother enhances calf survival and reproduction in Asian elephants

Usually animals reproduce into old age, but a few species such as humans and killer whales can live decades after their last reproduction. The grandmother hypothesis proposes that such life-history evolved through older females switching to invest in their existing (grand) offspring, thereby increasing their inclusive fitness and selection for post-reproductive lifespan. However, positive grandmother effects are also found in non-menopausal taxa, but evidence of their associated fitness effects is rare and only a few tests of the hypothesis in such species exist. Here we investigate the grandmother effects in Asian elephants. Using a multigenerational demographic dataset on semi-captive elephants in Myanmar, we found that grandcalves from young mothers (< 20 years) had 8 times lower mortality risk if the grandmother resided with her grandcalf compared to grandmothers residing elsewhere. Resident grandmothers also decreased their daughters' inter-birth intervals by one year. In contrast to the hypothesis predictions, the grandmother's own reproductive status did not modify such grandmother benefits. That elephant grandmothers increased their inclusive fitness by enhancing their daughter's reproductive rate and success irrespective of their own reproductive status suggests that fitness-enhancing grandmaternal effects are widespread, and challenge the view that grandmother effects alone select for menopause coupled with long post-reproductive lifespan