Blood is thicker than water for childcare, but friends win at everyday practical help

People in Finland are more likely to receive demanding childcare help from siblings than from friends, but more likely to receive everyday practical help from friends, according to research published in Evolution & Human Behavior.

Why do people help one another, and does it matter whether the person in need is family or a friend? Inclusive fitness theory predicts that people should be especially likely to help genetic relatives because doing so can indirectly support the survival and reproduction of shared genes. Prior research has often supported this idea, showing that people tend to direct more altruism toward close biological kin than toward more distant relatives, step-kin, in-laws, or unrelated individuals. At the same time, some studies have found that friends can receive as much help as relatives, or even more, depending on the type of help being studied.

Antti O. Tanskanen and colleagues examined this question by focusing on the actual help people reported receiving from full siblings and friends. This distinction matters because full siblings share, on average, about half their genes, while friends usually do not share any genetic relatedness. The authors were especially interested in whether the type and cost of the help would matter.

Childcare help may be particularly meaningful from an evolutionary perspective because it can directly support a relative’s reproductive success, while practical help and financial support may be shaped more by everyday need, availability, and social closeness. The researchers therefore expected childcare help to be more common from siblings than from friends. They expected practical help and financial support might be more evenly distributed, though still somewhat more common from siblings.

The study used population-based survey data from the Generational Transmissions in Finland project, which collects information about social support among kin and non-kin, as well as sociodemographic information. The survey was collected in autumn 2018 by Statistics Finland and originally included 1,945 younger and middle-aged Finnish adults. Participants could complete the survey online or using a paper-and-pencil questionnaire, although nearly 80% responded online. At the time of data collection, participants ranged in age from 19 to 56 years old.

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For the present study, the researchers included only participants who had at least one living full sibling and one living friend, and who had complete data on the study variables. This produced a final sample of 1,254 adults.

Participants reported whether they had received three kinds of help during the past 12 months: practical help, financial support, and childcare help. Each form of help was coded as whether it had been received or not, using a 0 = no and 1 = yes scale. For siblings, participants could report help received from up to their four oldest full siblings; when there was more than one sibling, the researchers selected the sibling from whom the participant had received the greatest amount of that particular type of help.

For friends, participants answered parallel questions about the friend from whom they had received the most help. Practical help and financial support were asked of all eligible participants, while childcare help was asked only of participants who had at least one child aged 13 or younger.

The final analyses included 1,226 observations from 613 individuals for childcare help, and 2,508 observations from 1,254 individuals for practical help and financial support. The researchers also considered participant sex, age, education, financial condition, partnership status, number of children, number of siblings, and number of close friends.

The findings showed that the source of help depended strongly on the type of help. Participants were more likely to receive childcare help from siblings than from friends, with predicted probabilities of 45.5% for siblings compared with 36.7% for friends. This supported the authors’ prediction that childcare, as a demanding and fitness-relevant form of help, would be more likely to come from close kin.

Financial support was also slightly more common from siblings than from friends, with predicted probabilities of 4.5% versus 3.4%, but this difference was not statistically significant. The authors noted that financial support from anyone was rare overall in this Finnish sample.

The pattern was different for practical help. Participants were more likely to receive practical help from friends than from siblings, with predicted probabilities of 58.3% for friends compared with 45.1% for siblings. This finding suggests that lower-cost or more everyday forms of support may often come from friends, possibly because friends may live closer or be more available for routine help.

When examining sex differences, the researchers found no significant sex-based differences in the sibling-versus-friend pattern for childcare help or financial support. However, both men and women were more likely to receive childcare help from friends and siblings than men were.

Practical help also varied by sex: both women and men were more likely to receive practical help from friends than from siblings, but men were especially likely to receive practical help from friends. The authors suggested that this may reflect broader differences in how male and female friendships are often organized, with male friendships being more centered around doing activities together.

An important limitation is that the authors could not control for the characteristics of the specific siblings and friends included in the analyses. In particular, they could not account for geographic distance, even though proximity may strongly affect whether someone is available to provide practical help. Previous research has shown that friends generally live closer to one another than siblings do.

Overall, the findings suggest that siblings may be especially important sources of higher-cost, family-relevant support, while friends may play a larger role in everyday practical assistance.

The research “Altruism among siblings vs. friends in a contemporary affluent population” was authored by Antti O. Tanskanen, Mirkka Danielsbacka, and Robin I.M. Dunbar.