Why would plants give resources to a fungus that goes on to give them to a neighboring plant—a potential competitor? At first glance it looks like altruism. Evolutionary theory doesn’t cope well with altruism because altruistic behavior benefits the receiver at the cost of the donor. If a plant donor assists a competitor at a cost to itself, its genes are less likely to make it into the next generation. If the altruist’s genes don’t make it into the next generation, the altruistic behavior will soon be weeded out.
