According to evolutionary theory, natural selection has designed individuals to behave selfishishly; selfish individuals are likely to end up with more resources and therefore more offspring. But many species (including humans, some rock musicians, politicians, and everyday citizens among them) do co-operate.
Traditionally, scientists have explained the evolution of co-operation using the idea of kin selection. Help to relatives (who share your genes) makes sense if it means your relative will have more children who will carry your genes into the next generation. Therefore, relatives are expected to help more. However, in a study published today in the Proceedings of the Royal Society, McMaster University researchers show that in certain situations the reverse is true: unrelated individuals help more.
Sigal Balshine, associate professor of in the Department of Psychology, Neuroscience & Behaviour at McMaster and her graduate student Kelly Stiver have been studying a small species of African cichlid fish that live in groups with a dominant breeding pair and non-breeding helpers. All individuals (helpers and breeders) co-operate to defend the young and the territory. The researchers combined behavioural observations with genetic analyses of relatedness in these fish groups and found that under specific ecological and demographic conditions unrelated individuals must "pay-to-stay" in the group and therefore may help more.
"This fish species is particularly interesting because breeders and helpers are not close relatives, but they co-operate nevertheless," says Balshine. "We think that unrelated individuals may be required to "pay more" by doing m ore work than related individuals in order to be allowed access and enjoy the benefits of being part of a group."
Using a combination of laboratory experiments and underwater field observations in Lake Tanganyika (Zambia), Stiver and Balshine examined how the help provided to breeders varied by how related the helpers were to the breeders. "While some helpers work or care for young because they are related to the dominant breeders, we also observed that other unrelated helpers work as a kind of rent payment," says Stiver.
Like in a commune or a kibbutz where non-relatives work together to achieve a common goal, these helper fish donate their time and energy to the group in exchange for the safety of living within the group. In a sense, these tiny African fish take a larger than usual worldview, and continued studies of co-operation in this species and other animals may shed light on the factors promoting co-operation in our own species.
The paper is available online at www.journals.royalsoc.ac.uk/link.asp?id=4elc7n9j2au5tb95.
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