Study on kin selection explores the evolutionary basis of sibling rivalry

Is it possible that our tendencies toward sibling rivalry may have an evolutionary basis? Recent research suggests this is a possibility, and is influenced by an evolutionary process called kin selection.

In nature, various species are more likely to help individuals who are more closely related to themselves. Researchers have suggested that helping one’s relatives may act as a form of natural selection—called kin selection.

Like the model of natural selection proposed by Darwin, kin selection suggests that we pass on our genes by helping others survive if they are genetically related to us. Relatives like cousins, aunts, and nephews also share some of our genes, and we can pass on our genes by helping these relatives survive. Thus, the more related two individuals are, the more likely they should be to help each other.

The idea of kin selection has become even more important today as the number of blended and non-traditional families continues to increase. Children today may live in a household mixed with biological siblings, half siblings, or unrelated siblings. If kin selection leads more closely-related individuals to help each other, then less-related individuals should experience more conflict. Is it possible that relatedness could affect sibling conflict?

Published in Evolutionary Psychological Science, Catherine Salmon and Jessica Hechman sought out to answer this question. They examined the impact of siblings’ gender, relatedness, and co-residence on the amount of sibling conflict they experienced. They predicted that less-related siblings would have more sibling conflict than more closely-related individuals.

The greatest amount of reported conflict happened between non-biological siblings, as predicted. However, biological siblings reported greater conflict than half-siblings, who reported the least amount of conflict. Siblings who were closer in age reported greater conflict than siblings who were farther apart in age. In addition, the longer siblings had lived together, the more reported conflict they had.

The researchers also wanted to see whether conflict differed for boys and girls. Children reported more conflict with siblings who were the same sex as themselves; boys were more likely to fight with their brothers, and girls were more likely to fight with their sisters. The authors reported that, “brothers did have more intense, sometimes physical, conflict than sisters or brother–sister pairs”.

Based on these findings, should parents be concerned? Probably not, say researchers. In fact the authors point out that, “a number of researchers have suggested that sibling conflict is a normal part of human development.”

In sum, this research examined how evolution may be continually influencing sibling rivalries. These findings shed light on the roots of sibling conflict, and the factors that may lead to greater or lesser sibling rivalry.


  1. is it possible !? it is evident . an observation of animals in the natural world will quicky demonstrate the source of such innate behavior in Humans

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    is it possible ! ? it is evident . an observation of animals in the natural world will quickly demonstrate the source of such innate behavior in Humans