Altruism–selfless behavior–is widespread in nature. Organisms from microbes to mammals help others by warning about predators, caring for others’ offspring, foraging to retrieve food for nest mates, cooperating in the hunt, and communicating the location of food.
But not all acts of altruism are alike, says a new study. From bees and wasps that die defending their nests to elephants that cooperate to care for young, the environment plays a role in the origins of altruism, say two biologists from Indiana University Bloomington. The researchers have developed a new mathematical model that pinpoints when environmental conditions favor one form of altruism over another.
Michael Wade and J. David Van Dyken, now an NSF postdoctoral fellow and recent PhD student in Wade’s laboratory at IU Bloomington, published their findings in a recent issue of the international journal Evolution. Their model predicts that creatures will help each other in different ways depending on whether key resources such as food and habitat are scarce or abundant.
Most mathematical models assume that all forms of altruism provide similar perks. But the benefits of altruism are different for different behaviors, says Wade, a Distinguished Professor of biology at IU Bloomington and a visiting scholar at the National Evolutionary Synthesis Center located in Durham, NC. For example, some creatures cooperate for the sake of defense, others to support reproduction (such as termites who enable queens to lay hundreds to millions of eggs), and others to increase the availability of food.
The researchers conclude that when key local resources such as food or habitat are scarce, altruistic behaviors that provide more of those resources or that use them more efficiently will be favored. Think of lions banding together to hunt and take down prey or honey bees sharing the location of food as they forage.
But if resources are abundant, then altruistic behaviors that help others live longer or produce more offspring will take precedence. Animals such as songbirds or chimpanzees, for example, make alarm calls to warn nearby group members of approaching predators, braving danger to protect others.
“The bottom line is that the way creatures are likely to help each other when times are tight is different from how they’re likely to help each other in times of plenty,” Wade says.
The co-authors say that too many studies– ranging from investigations of human economic behavior to laboratory experiments with microbes—conflate altruism types. “Identifying the specific ecological function of an altruistic trait is not only essential to understanding its evolution, it is required to inform experimental design, to avoid false inferences from experimental results, and to accurately predict responses of species to specific medical or management interventions,” they write.