Alloparenting in humans: fitness consequences of aunts and uncles on survival in historical Finland

Nitsch, Aïda; Faurie, Charlotte; Lummaa, Virpi

doi:10.1093/beheco/art126

Cited by 20 publications

(19 citation statements)

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“…For instance, in the case of human families, a study on an Irish population suggested that philopatric siblings increased the overall amount of resources of the family, thereby benefitting the whole family (Strassmann & Clarke, ). In contrast, another study showed that the presence of nondispersed individuals in the family did not enhance the survival of their nephews and nieces (Nitsch et al ., ). In our population, unmarried siblings could remain in the family household until marriage (Moring, ), which suggests that dispersal decisions might be under individual rather than parental control.…”

Section: Discussionmentioning

confidence: 99%

“…Offspring resident at their parents were working at the farm or performing household tasks (Moring, ). However, no effect of the resident nonreproducing siblings on survival of other children residing in the same parish was detected in a previous study (Nitsch et al ., ). Therefore, the predominant household was composed of the eldest son, his wife, their children, his parents and one or more unmarried siblings (Moring, ).…”

Section: Methodsmentioning

confidence: 99%

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Sibship effects on dispersal behaviour in a pre‐industrial human population

Nitsch

Lummaa

Faurie

2016

J of Evolutionary Biology

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Understanding dispersal behaviour and its determinants is critical for studies on life-history maximizing strategies. Although many studies have investigated the causes of dispersal, few have focused on the importance of sibship, despite that sibling interactions are predicted to lead to intrafamilial differences in dispersal patterns. Using a large demographic data set from pre-industrial Finland (n = 9000), we tested whether the sex-specific probability of dispersal depended on the presence of same-sex or opposite-sex elder siblings who can both compete and cooperate in the family. Overall, following our predictions, the presence of same-sex elder siblings increased the probability of dispersal from natal population for both sexes, whereas the number of opposite-sex siblings had less influence. Among males, dispersal was strongly linked to access to land resources. Female dispersal was mainly associated with competition over availability of mates but likely mediated by competition over access to wealthy mates rather mate availability per se. Besides ecological constraints, sibling interactions are strongly linked with dispersal decisions and need to be better considered in the studies on the evolution of family dynamics and fitness maximizing strategies in humans and other species.

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Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Sibship effects on dispersal behaviour in a pre‐industrial human population

Nitsch

Lummaa

Faurie

2016

J of Evolutionary Biology

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“…This is because aunts and uncles are not expected to invest as heavily in their nieces and nephews as they would their own children. In 18th and 19th century Finland, for example, the presence of non-reproductive aunts and uncles was weakly or negatively correlated with the survival of their nieces and nephews (Nitsch, Faurie & Lummaa, 2014). Therefore, unlike the parent–offspring relationship, niece and nephews are less likely to be negatively impacted by the dilution of investment (e.g., a negative correlation in LRS is evidence of a quantity–quality tradeoff between offspring number and offspring fitness).…”

Section: Discussionmentioning

confidence: 99%

The impact of parental investment on lifetime reproductive success in Iceland

Lynch

2017

PeerJ

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BackgroundDemonstrating the impact that parents have on the fitness of their children is a crucial step towards understanding how parental investment has affected human evolution. Parents not only transfer genes to their children, they also influence their environments. By analyzing reproductive patterns within and between different categories of close relatives, this study provides insight into the genetic and environmental effects that parents have on the fitness of their offspring.MethodsWe use data spanning over two centuries from an exceptionally accurate Icelandic genealogy, Íslendingabók, to analyze the relationship between the fertility rates of close relatives. Also, using genetic data, we determine narrow sense heritability estimates (h2) to further explore the genetic impact on lifetime reproductive success. Finally, we construct four simulations to model the expected contribution of genes and resources on reproductive success.ResultsThe relationship between the reproduction of all full sibling pairs was significant and positive across all birth decades (r = 0.19) while the reproductive relationship between parents and offspring was often negative across many decades and undetectable overall (r = 0.00) (Fig. 1 and Table 1). Meanwhile, genetic data among 8,456 pairs of full siblings revealed a narrow sense heritability estimate (h2) of 0.00 for lifetime reproductive success. A resources model (following the rule that resources are transmitted from parents to children, distributed equally among siblings, and are the only factor affecting reproductive success) revealed a similar trend: a negative relationship between parent and offspring reproduction (r = − 0.35) but a positive relationship among full siblings (r = 0.28). The relationship between parent and offspring lifetime reproductive success (LRS) and full sibling LRS was strongly and positively correlated across time (r = 0.799, p < 0.001). Similarly, the LRS among full siblings was positively correlated with both the LRS among half siblings (r = 0.532, p = 0.011) and the relationship between the LRS of aunts and uncles with their nieces and nephews (r = 0.438, p = 0.042).DiscussionWe show that an individual’s lifetime reproductive success is best predicted by the reproduction of their full and half siblings, but not their parents, grandparents or aunts and uncles. Because all siblings share at least one parent, we believe parental investment has had an important impact on fitness. Overall, these results indicate that direct parental investment, but not genes, is likely to have had an important and persistent impact on lifetime reproductive success across more than two centuries of Icelandic history.

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“…More rigorously, Nitsch, Faurie, and Lummaa (2014) found almost no effect of childless aunts and uncles on survival of nieces and nephews in 18th century Finland. Sear and Mace (2008) reviewed 45 studies of effects of kin on child survival and found no effects of aunts, but positive effects of maternal grandmothers and siblings.…”

Section: A Case Study: Age and Parity In Slovakiamentioning

confidence: 97%

The formal demography of kinship II: Multistate models, parity, and sibship

Caswell¹

2020

Preprint

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BackgroundRecent kinship models focus on the age structures of kin as a function of the age of the focal individual. However, variables in addition to age have important impacts. Generalizing age-specific models to multistate models including other variables is an important and hitherto unsolved problem.ObjectivesOur aim is to develop a multistate kinship model, classifying individuals jointly by age and other criteria (generically, “stages”).MethodsWe use the vec-permutation method to create multistate projection matrices including age- and stage-dependent survival, fertility, and transitions. These matrices operate on block-structured population vectors that describe the age×stage structure of each kind of kin, at each age of a focal individual.ResultsThe new matrix formulation is directly comparable to, and greatly extends, the recent age-classified kinship model of Caswell (2019a). As an application, we derive a model that includes age and parity. We obtain, for all types of kin, the joint age×parity structure, the marginal age and parity structures, and the (normalized) parity distributions, at every age of the focal individual. We show how to use the age×parity distributions to calculate the distributions of sibship sizes of kin.As an example, we apply the model to Slovakia (1960–2014). The results include a dramatic shift in the parity distribution as the frequency of low-parity kin increased and that of high-parity kin decreased.ContributionThe new model extends the formal demographic analysis of kinship to age×stage-classified models. In addition to parity, other stage classifications, including marital status, maternal age effects, and sex are now open to analysis.

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Alloparenting in humans: fitness consequences of aunts and uncles on survival in historical Finland

Cited by 20 publications

References 53 publications

Sibship effects on dispersal behaviour in a pre‐industrial human population

Sibship effects on dispersal behaviour in a pre‐industrial human population

The impact of parental investment on lifetime reproductive success in Iceland

The formal demography of kinship II: Multistate models, parity, and sibship

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