Proc. R. Soc. B doi:10.1098/rspb.2010.1572 (2010)

Among humans, a lurking mother is not viewed as a great aphrodisiac. Not so among our cousins, the bonobos (Pan paniscus).

Martin Surbeck and his colleagues at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, observed a community of bonobos at Salonga National Park in the Democratic Republic of the Congo. Despite the species' reputation as egalitarian and sexually freewheeling, the team found that males arranged themselves in a rigid linear dominance hierarchy. As expected, higher-ranking males mated more often with fertile females, but there was a twist. Lower-ranked males were more successful when their mothers were around.

When every male's mother was present, the alpha bonobo's share of matings with fertile females declined from 41% to a mere 25%. The authors propose several possible reasons for this influence, one of which was clear to see: mothers were spotted helping to fight off their sons' sexual competitors.