Oh half-brother, where art thou? The boundaries of full- and half-sibling interaction

This study investigates sibling and “extended sibling” relations. Extended sibling relations refer to relations between nieces or nephews and aunts or uncles. Both cooperation and conflict between kin are investigated. We use an evolutionary family sociological framework for analysing kin relations in present day Finland and the UK. Cooperation is measured by kin support, emotional closeness, and contact frequency, while the outcome of sibling conflict is measured by toddlers’ unintended injuries, young adolescents’ reports of how much siblings picked and hurt each other, and adults’ self-reported disagreements with siblings. The study includes seven original articles and an introductory chapter.Article I shows that 3-year-old British children who live in the same household with their full siblings have a lower risk of unintended home injuries than do children who live with their full and half siblings or only with their half siblings. Article II finds that 11-year-old British children living with their full siblings only were more likely to report hurting or picking between siblings compared with children who live with their half siblings only. Article III describes two generations of adult Finns and shows that both younger (mean age 36 years old) and older (mean age 65 years) generations have more contacts with full than half siblings and more contacts with the children of full siblings than with children of half siblings. Based on article IV, older and younger Finns have more contact with their sisters’ children compared to their brothers’ children. Article V finds that childless younger women in Finland provide more childcare to their siblings’ children than do younger mothers. However, mothers and childless women provide equal amounts of support to their aunts and uncles. According to article VI, younger Finnish adults who have half siblings are more likely to have encountered unequal maternal treatment than younger adults who have full siblings only. Article VII shows that younger and older Finns are more likely to have conflicts with their full siblings than with their half siblings.Combined, these results show that kin relations tend to differ both between maternal and paternal kin and between full and half siblings. Moreover, kin support is more likely to flow from older individuals to younger ones than vice versa. Finally, parental unequal treatment seems to shape relations between siblings. At the end of the introduction chapter, policy and practical implications of the results are discussed.

To investigate the efficacy of different numbers of microhaplotype (MH) loci and the introduction of different reference samples on the identification of full sibling, half sibling and differentiation between full sibling and half sibling kinships, and to explore the effect of changing mutation rate on sibling testing. First, a family map involving three generations was established, and four full sibling identification models, five half sibling identification models and five models distinguishing full and half siblings were constructed for different reference samples introduced. Based on the results of the previous study, two sets of nonbinary SNP-MH containing 34 and 54 loci were selected. Based on the above MH loci, 100 000 pairs of full sibling vs. unrelated individuals, 100 000 pairs of half sibling vs. unrelated individuals and 100 000 pairs of full sibling vs. half sibling were simulated based on the corresponding sibling kinship testing models, and the efficacy of each sibling kinship testing model was analyzed by the likelihood ratio algorithm under different thresholds. The mutant rate of 54 MH loci was changed to analyze the effect of mutation rate on sibling identification. In the same relationship testing model, the systematic efficacy of sibling testing was positively correlated with the number of MH loci detected. With the same number of MH loci, the efficacy of full sibling testing was better than that of uncle or grandfather when the reference sample introduced was a full sibling of A, but there was no significant difference in the identification efficacy of the four reference samples introduced for full sibling and half sibling differentiation testing. In addition, the mutation rate had a slight effect on the efficacy of sibling kinship testing. Increasing the number of MH loci and introducing reference samples of known relatives can increase the efficacy of full sibling testing, half sibling testing, and differentiation between full and half sibling kinships. The level of mutation rate in sibling testing by likelihood ratio method has a slight but insignificant effect on the efficacy.

FC02-01 - Risk for hospitalization for schizophrenia and affective disorders among full and half siblings of probands with schizophrenia: A population-based study

Cancer risk in siblings of children with congenital malformations

PurposeTo investigate the association between sibling relatedness and pubertal development in girls and boys. MethodsThis cohort study consisted of 10,657 children from the Puberty Cohort, Denmark. Information on sibling relatedness was obtained by self-report. Information on pubertal markers was obtained half yearly from age 11 and throughout puberty. Mean age difference at attaining pubertal markers was estimated using interval-censored regression models according to sibling relatedness (full, half and/or step siblings; half and/or step siblings; no siblings; relative to full siblings). ResultsGirls with both full, half and/or step siblings (−1.2 (CI 95 %: −2.5; 0.1) months), only half- and/or stepsiblings (−2.2 (CI 95 %: −3.7; −0.7) months), and no siblings (−5.5 (CI 95 %: −8.5; −2.5) months) entered puberty earlier than girls with full siblings. Boys with full, half and/or step siblings (−1.4 (CI 95 %: −2.7; −0.1) months), only half and/or step siblings (−1.2 (CI 95 %: −3.0; 0.6) months), and no siblings (−4.5 (CI 95 %: −8.8; −0.3) months) entered puberty earlier than boys with full siblings. ConclusionsChildren with sibling relatedness other than full siblings entered puberty earlier than their peers with full siblings even after adjustment for parental cohabitation status, childhood body mass index and childhood internalizing and externalizing symptoms.

Populações de cinco diferentes tipos de acasalamento, submetidas à seleção baseada no melhor preditor linear não-viesado (BLUP), foram avaliadas quanto às perdas genéticas por fixação de alelos desfavoráveis e limite da seleção, durante 50 gerações. Foram utilizados dados simulados na obtenção do genoma dos indivíduos de todas as populações. Uma característica quantitativa de herdabilidade 0,10 foi estudada em populações de seleção, com a seguinte estrutura de dados: razão sexual de 10, 20, 25 e 50 e tamanho efetivo da população de 36,36, 19,05, 15,38, e 7,84, respectivamente. Para cada razão sexual, formaram-se populações correspondentes aos tipos de acasalamento efetuados entre os reprodutores, em todas as gerações: acasalamentos preferenciais entre meios-irmãos e irmãos completos, acasalamentos preferenciais entre meios-irmãos, acasalamentos ao acaso, exclusão de acasalamentos entre irmãos completos e exclusão de acasalamentos entre meios-irmãos e irmãos completos. Valores percentuais mais baixos para locos fixados desfavoravelmente e limite da seleção mais alto foram observados na menor razão sexual (d= 10), na qual houve também melhor distinção entre os tipos de acasalamento estudados.

Background Due to the increasing family instability and multipartner fertility in Western countries, more children have half- and stepsiblings. While numerous studies link family instability and complexity with mental health problems, the focus has typically been on the parents while a small but growing literature suggest that sibling constellations with half- and stepsiblings may also be important for adolescent mental health. Methods This study is based on administrative register data of all children born in Finland in 2000 and residing there at ages 0 − 15 (n = 56,372). We identified the biological parents, their cohabiting partners, and any full, half and step siblings that the index child has from birth to age 15. We used Cox proportional-hazards models to compare differences in psychiatric disorders from age 16 to 19 for boys and girls by different sibling constellations. Psychiatric disorders were identified as any disorders treated in specialized outpatient or hospital care (n = 7,999). Results Almost one in five children in the birth cohort had a cohabiting half sibling and almost 4% had a step sibling. Psychiatric disorders in late adolescence were more prevalent among children in different sibling compositions with half or step siblings. For example, the preliminary results show that adjusting for confounders such as socioeconomic status and living with both biological parents or not, boys and girls with an older half sibling had a 44% (95% confidence interval 34-55) higher risk of psychiatric disorders when compared to children with biological siblings only. The corresponding difference in risk for those with younger half siblings was 24% (11-55). Conclusions Psychiatric disorders were more prevalent in late adolescence among children with half and/or step siblings. Future studies on family complexity are likely to benefit from including information on sibling characteristics in addition to those of the parents. Key messages • Adolescents growing up with half or stepsiblings had a higher prevalence of psychiatric disorders in late adolescence. • More studies on sibling composition and adolescent psychiatric disorders are needed to inform the type of supportive measures that may benefit children living with half and stepsiblings.

Journal Digest: Home Environment; Postpartum Mental Illness; Placebo in Psychedelic Study; Single Gene Mutation; Topiramate

Sibling relations are typically close but ambivalent, including both altruism and competition. Full siblings are often assumed to exhibit more altruism and less competition than half-siblings. However, previous empirical findings indicate that this assumption may not hold for sibling conflicts in contemporary humans. We study self-reported occurrence of sibling conflicts among adults in two generations with nationally representative data from the Generational Transmissions in Finland surveys in 2012. Respondents represent an older generation (born between 1945 and 1950, n = 2,015) and their adult children (born between 1962 and 1993, n = 1,565). Based on kin selection and parent-offspring conflict theory we expect reports of any conflict to be more likely between full siblings than half siblings, between maternal half siblings than paternal half-siblings, and among the younger generation compared to the older generation. Results mostly support our hypotheses. Full siblings were more likely to report conflicts than were maternal and paternal half siblings in the younger generation. In the older generation, full siblings were more likely to report conflicts with paternal but not maternal half siblings. The younger generation was also more conflict-prone than the older. Results held when controlling for contact frequency, emotional closeness, unequal parental treatment, and several socioeconomic variables, as well as for within-family effects. Thus, although full siblings are typically closer and have more contact in adulthood than half siblings do, they also appear to have more conflicts. We suggest that this can be explained by diluted resource competition over parental investment between half siblings in societies with serial monogamy.

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.

Diferentes tipos de acasalamentos foram avaliados, por meio de dados simulados, em populações submetidas à seleção com base no BLUP, durante 50 gerações. Considerou-se uma característica quantitativa de herdabilidade 0,10 e a seguinte estrutura das populações de seleção: valores de razão sexual: 10, 20, 25 e 50; números de machos selecionados por geração: 10, 5, 4 e 2; tamanhos efetivos de população: 36,36; 19,05; 15,38; e 7,84, respectivamente. Em cada valor de razão sexual, as populações foram acasaladas segundo um dos tipos de acasalamentos: acasalamentos preferenciais de meios-irmãos e irmãos completos, acasalamentos preferenciais entre meios-irmãos, acasalamentos ao acaso, exclusão de acasalamentos entre irmãos completos e exclusão de acasalamentos de meios-irmãos e irmãos completos. Os parâmetros genéticos avaliados foram valores fenotípicos médios e consangüinidade média por geração. No menor valor de razão sexual, observou-se melhor desempenho fenotípico de todos os tipos de acasalamentos. Os tipos de acasalamentos que não permitiram acasalar irmãos proporcionaram maiores ganhos fenotípicos e foram os mais efetivos no controle da consangüinidade, no curto prazo, embora não tivessem impedido seu aumento e acúmulo, ao longo das gerações.

An adoption study of genetic effects on obesity in adulthood was carried out in which adoptees separated from their natural parents very early in life were compared with their biological full and half siblings reared by their natural parents. The adoptees represented four groups who by sampling from a larger population were categorised as either thin, medium weight, overweight, or obese. Weight and height were obtained for 115 full siblings of 57 adoptees and for 850 half siblings of 341 adoptees. In full siblings body mass index (kg/m2) significantly increased with weight of the adoptees. Body mass index of the half siblings showed a steady but weaker increase across the four weight groups of adoptees. There were no significant interactions with sex of the adoptees, sex of the siblings, or (for the half siblings) sex of the common parent. In contrast with the findings in half siblings and (previously) the natural parents there was a striking, significant increase in body mass index between full siblings of overweight and obese adoptees. The degree of fatness in adults living in the same environment appears to be influenced by genetic factors independent of sex, which may include polygenic as well as major gene effects on obesity.

Half siblings are brothers and sisters who share only one biological parent and are thus, half biologically related. Although half siblings may be the result of extramarital/partnership affairs or post-bereavement, most are the result of a divorce and remarriage. Half sibling research is rare, and existing research and even national and international statistical reporting agencies often incorrectly conflate half siblings with stepsiblings. Research that can be found on half siblings often illustrates a “deficit-comparison” approach where half and stepsiblings are compared to full biological siblings and studied for how they fall short of biological sibling outcomes. Early research speculates that children who reside with half siblings experience poorer educational outcomes, report significantly more depressive symptoms, exhibit poorer coping skills, are more likely to engage in risky behavior such as early sexual activity and drug and alcohol use, and have more strained sibling and parental relationships compared to those with no half siblings or those with only full biological siblings. The challenges that exist for half sibling relationships are often hypothesized as associated with either family structure (half siblings located within a complex stepfamily) or explained through evolutionary perspectives of Darwinian fitness. However, research on half siblings overall is mixed, with studies also positing these outcomes are not due to the presence of half siblings and that there are instead positive implications from having a half sibling on individual outcomes, sibling relationship quality, and overall family functioning. Overall, half siblings can form quality relationships and half brothers and sisters who share a residence, are closer in age, of the same gender, spend more quality time with one another, have parents who prosaically intervene on their behalf, and who emphasize their positive relationship and connection through addressing terms and sharing backstories of their family’s origins are more likely to report a positive relationship.

Two studies investigated whether perceived closeness of siblings, and aggression between siblings, were associated with genetic relatedness. In following Hamilton’s rule, we predicted that as the coefficient of relatedness between siblings increased, emotional closeness would also increase while conflict would decrease. Contrary to the predictions, we found no effect of genetic relatedness in Study 1 when we compared participants’ (n = 240) ratings of emotional closeness; participants also reported significantly higher levels of conflict with full siblings than with half siblings. In Study 2, participants (n = 214) also reported a higher frequency of physical aggression with full siblings than with half siblings. These findings were contrary to the prediction from Hamilton’s rule. We discuss them in relation to parental investment in biological and non-biological offspring.

A simulation study illustrates the effects of the inclusion of half-sib pairs as well as the effects of selective genotyping on the power of detection and the parameter estimates in a sib pair analysis of data from an outbred population. The power of QTL detection obtained from samples of sib pairs selected according to their within family variance or according to the mean within family variance within half sib family was compared and contrasted with the power obtained when only full sib pair analysis was used. There was an increase in power (4–16%) and decrease in the bias of parameter estimates with the use of half-sib information. These improvements in power and parameter estimates depended on the number of the half sib pairs (half sib family size). Almost the same power as that obtained using all the available sib pairs could be achieved by selecting only 50–60% the animals. The most effective method was to select both full and half sib pairs on the basis of high within full sib family variance for the trait in question. The QTL position estimates were in general slightly biased towards the center of the chromosome and the QTL variance estimates were biased upwards, there being quite large differences in bias depending on the selection method.