A team of South African and English zoologists has found the means by which cooperative mammal societies benefit from having a lot of helping paws, according to a report in Friday's Science. Several different mechanisms could benefit the young of cooperative species in large groups, including better protection from predators and wider foraging. But the new report shows that the ratio of helpers to pups has a powerful effect on the weight gain and survival of Kalahari meerkat young, and even benefits the helpers.

To study the effect of helper-young ratios without varying the ability of a meerkat family to protect against predation or forage widely, the researchers either kidnapped pups or added them to groups in the wild. All the adult members of a meerkat group, which can number from two to 30, assist in the feeding of pups. The meerkats in the study made no distinction between their own young and the introduced pups. When the ratio of helpers to pups was increased, the pups gained weight faster, stayed heavier throughout their first year of life and had greater survival rates. When the helper-pup ratio decreased, the meerkat pups added weight more slowly, grew into smaller adults and survived less often.

An increased helper-pup ratio also slightly increased weight gain among the helpers, whereas a decreased helper-pup ratio had a pronounced effect on the helpers' weights. Because only one breeding pair are the parents of over 80 percent of the young in a meerkat group, this effect should benefit the next generation as well. When more young survive to become adult helpers, they reduce the burden on each individual. Mammal species such as our own respond negatively to increased group size. Species whose parents feed their young without any outside assistance feel only competition from other adults. But for the meerkats of southern Africa, each set of paws is a help to all.