In a world supposedly governed by ruthless survival of the fittest, why do we see acts of goodness in both animals and humans? This problem plagued Charles Darwin in the 1850s as he developed his theory of evolution through natural selection. Indeed, Darwin worried that the goodness he observed in nature could be the Achilles heel of his theory. Ever since then, scientists and other thinkers have engaged in a fierce debate about the origins of goodness that has dragged politics, philosophy, and religion into what remains a major question for evolutionary biology.

The Altruism Equation traces the history of this debate from Darwin to the present through an extraordinary cast of characters-from the Russian prince Petr Kropotkin, who wanted to base society on altruism, to the brilliant biologist George Price, who fell into poverty and succumbed to suicide as he obsessed over the problem. In a final surprising turn, William Hamilton, the scientist who came up with the equation that reduced altruism to the cold language of natural selection, desperately hoped that his theory did not apply to humans.

Hamilton's Rule, which states that relatives are worth helping in direct proportion to their blood relatedness, is as fundamental to evolutionary biology as Newton's laws of motion are to physics. But even today, decades after its formulation, Hamilton's Rule is still hotly debated among those who cannot accept that goodness can be explained by a simple mathematical formula. For the first time, Lee Alan Dugatkin brings to life the people, the issues, and the passions that have surrounded the altruism debate. Readers will be swept along by this fast-paced tale of history, biography, and scientific discovery.

• Social Behavior