Are elder siblings helpers or competitors?

Nov 22, 2012
Are elder siblings helpers or competitors?
Credit: Firemom

Having elder siblings decreases mortality risk in childhood, but same-sex elder siblings are associated with lower marriage rates and fewer children for their younger siblings in adulthood, according to the results of a long-term study published in Proceedings of the Royal Society B today.

Analysis was carried out at the University of Sheffield, on a large demographic dataset of preindustrial humans from Finland to study the effect of elder siblings. The findings demonstrate that family members often both cooperate and compete, and the benefits and costs of having elder siblings may vary across life and between sisters and brothers.

Aïda Nitsch and her colleagues found that the presence of elder siblings improved the chances of younger siblings surviving to , suggesting that despite a competition for parental resources, they may help rearing their .

Their study of around 10,000 and all of their nearly 30,000 offspring from 1750-1958 also found, however, that after reaching sexual maturity same-sex elder siblings' presence was associated with reduced reproductive success in the younger sibling, indicating the existence of competition among same-sex siblings.

Overall, lifetime fitness was reduced by same-sex elder siblings' presence and increased by opposite-sex elder siblings' presence. The study shows opposite effects of sibling interactions depending on their life-stage, and highlights the need for using long-term fitness measures, such as those used in this study, to understand the selection pressures acting on sibling interactions.

Interactions between siblings can have long-term psychological and developmental implications. Studying such interactions is pivotal for understanding how humans evolved such large and complex families.  

Explore further: Awarded a Pell Grant? Better double-check

More information: Nitsch, A., Faurie, C. and Lummaa, V. Are elder siblings helpers or competitors? Antagonistic fitness effects of sibling interactions in humans, Proceedings of the Royal Society B. dx.doi.org/10.1098/rspb.2012.2313

Related Stories

Sibling relationships reflect family dynamics

Nov 15, 2006

Most children in the United States grow up with sisters and brothers. Connections that usually last a lifetime, these relationships can be strained at times, especially during childhood. New research concludes that sibling ...

Britain may allow more savior siblings

Aug 02, 2007

British couples may be allowed to use in vitro fertilization to select embryos that are a genetic match to siblings with non-fatal illnesses.

Inherited wealth leads to sibling rivalry

Jan 25, 2011

(PhysOrg.com) -- Sibling rivalry is driven by the transfer of wealth between generations, according to new research by anthropologists at the University of Bristol and Addis Ababa University.

The un-favorite child

Jan 19, 2009

(PhysOrg.com) -- “Mom always liked you best.” The Smothers Brothers aside, chances are if you’ve got a sibling, this is something you’ve either heard or said at some point in your life. Many people ...

Recommended for you

Awarded a Pell Grant? Better double-check

14 hours ago

(AP)—Potentially tens of thousands of students awarded a Pell Grant or other need-based federal aid for the coming school year could find it taken away because of a mistake in filling out the form.

Perthites wanted for study on the Aussie lingo

22 hours ago

We all know that Australians speak English differently from the way it's spoken in the UK or the US, and many of us are aware that Perth people have a slightly different version of the language from, say, Melbournians - but ...

User comments : 0