“In semiconductors, changes in the microscopic structure of a metal can affect how much electricity must be applied to ‘activate’ it, such that the amount of current passing through jumps from zero to a particular number. Similarly, a recent paper in Nature written by my colleagues predicted how large a financial reward (the electricity) is required for altruism to ‘turn on’ and spread through a group (the semiconductor). Some networks require a reward of $1.05, for example, and are pretty great conductors of altruism; some demand $100 or more, and are very difficult to activate.”