Many studies have failed to unequivocally show that helpers provide more help to closer relatives, as predicted by kin selection theory, thus compounding the problem.
Sister Sense
To provide stronger evidence for the kin selection idea, West and University of Edinburgh colleague Ashleigh Griffin decided to look instead at the kinds of species that are best able to distinguish between the nuclear family, distant relatives, and unrelated individuals.
The pair compared data from studies covering 18 different species, including dwarf mongooses, meerkats, Florida scrub jays, western bluebirds, and Australian magpies. They used statistical methods to reveal that species which show the most discrimination between relatives—and provide more help to closer relatives—are precisely those species where helpers got more bang for their buck.
"The extent to which individuals preferentially help [close relatives] is positively correlated with the benefit that helping provides," by increasing survival of the young, said West. Those species like the pied kingfisher and the Seychelles warbler, which are able to fledge many more young when assisted, are also the same species that are mostly likely to recognize close relatives.
"This study shows that you make discriminations much better when you have more to gain," commented evolutionary biologist Mark Pagel at the University of Reading in England, who commended the analysis.
When you totally forgo your own opportunity to reproduce, it's essential that you can discriminate family from strangers, said Pagel. "Otherwise you end up helping an unrelated animal, and you've blown it."
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