Evolutionary biologists Filippo Aureli of Liverpool John Moores University in Liverpool, UK, and Gabriele Schino of the Italian National Research Council's Institute of Cognitive Sciences and Technologies (ISTC-CNR) in Rome, have now combed through dozens of previous studies to quantify how often primates groomed relatives and non-relatives, and how often the favour was returned. They found that, contrary to the prevailing view, primates were more likely to groom others that had groomed them, regardless of their relatedness. Publishing their analysis in Ecology Letters1, the researchers report that reciprocity alone explained about 20% of the variability in grooming behaviour in 14 different species of primates, whereas kinship alone explained only 3%.
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