There are evolutionary advantages to living in a social group. Groups cooperate to hunt large prey, rear young, and defend territory. Group members experience reduced exposure to predation (safety in numbers), easier access to reproductive partners, and a rich learning environment. There are also evolutionary disadvantages to living in a social group, including increased exposure to disease and parasites…one would think. However, ecologists are learning this might not be a true in all cases.
The Science & Technology section of the May 30, 2015, issue of The Economist included an article titled Pack Power about grey wolves living in Yellowstone National Park. In 2007, a contagious and potentially deadly disease called mange began spreading through this population. Mange is caused by parasitic mites. Ecologists expected mange to appear more frequently in larger wolf packs because the more group members the greater the chance that one of the group contracts the disease and spreads it to his pack-mates. However, this is not what they found. Infection risk did not vary by pack size. Wolves living in large packs were no more likely to catch mange than wolves living in small packs or solitary wolves.
Still more interesting was the discovery that wolves living in large packs were five times less likely to die of mange compared to wolves that contracted the disease while living alone. Ecologists believe the higher survival rate among sick wolves living in large groups is due to social support. Pack-mates help sick wolves find and catch food, preventing starvation. I wonder if there is another, perhaps even stronger contributing factor. There is mounting evidence for social structuring of the microbiome. The microbiome is the community of bacteria living in an animal’s gut, mouth, skin and elsewhere on its body that help it digest food, make vitamins, and fight disease. Through physical interaction, animals share their microbiomes. For example, baboons that groom each other more frequently have more similar microbiomes. A wolf living in a large pack has more social relationships and presumably more physical contact with other wolves. Therefore, he may have access to a greater variety of health-promoting bacteria, resulting in a more diverse microbiome better suited for combatting illness. This hypothesis warrants testing.
As we learn more about the role of the microbiome in fending off disease, how might this new knowledge inspire biomimetic behavioral preventive therapies?