Consider some standard examples of design in nature: the aerodynamic wing of the bird, the concealing coloration of the moth, the dense fur of the polar bear. Darwin's insight was to explain these adaptations as a product of natural selection: individuals vary, some survive and reproduce better than others, and their properties are inherited by their offspring.
All of these adaptations are locally advantageous. Individuals possessing them survive and reproduce better than their immediate neighbors. Now consider some standard examples of social adaptations: the good Samaritan, the soldier who heroically dies in battle, the honest person who cannot tell a lie. We admire these virtues and call them social adaptations because they are good for others and for society as a whole--but they are not locally advantageous. Charitable, heroic, and honest individuals do not necessarily survive and reproduce better than their immediate neighbors who are stingy, cowardly, and deceptive.
How important is this problem? For Darwin, who was formulating the entire theory of evolution, it was one important problem among many. If we restrict our attention to the study of social behavior, however--what E.O. Wilson would later call Sociobiology--it is paramount. Most behaviors that we call prosocial require time, energy, and risk on the part of the prosocial individual. Most behaviors that we call antisocial deliver an immediate benefit to the antisocial individual. If most antisocial behaviors are locally advantageous and most prosocial behaviors are locally disadvantageous, then we have an enormous problem explaining the nature of prosociality, including the nature of human morality, from an evolutionary perspective.
Darwin was aware of this problem and proposed two types of solution. First, he observed that farmers routinely sacrifice some individuals for eating and select their traits by breeding their relatives. Individuals who altruistically sacrifice themselves for their relatives, such as the suicidal sting of the honeybee, might therefore evolve by natural selection. This idea anticipated what later would be called kin selection.
Second, Darwin observed that groups of prosocial individuals will survive and reproduce better than groups of antisocial individuals, even if antisocial individuals have the advantage over prosocial individuals within groups. Here is one of his canonical statements, using human moral virtues as an example (from Chapter 4 of Descent of Man).
It must not be forgotten that although a high standard of morality gives but a slight or no advantage to each individual man and his children over other men of the same tribe, yet that an increase in the number of well-endowed men and advancement in the standard of morality will certainly give an immense advantage to one tribe over another. There can be no doubt that a tribe including many members who, from possessing in a high degree the spirit of patriotism, fidelity, obedience, courage, and sympathy, were always ready to aid one another, and to sacrifice themselves for the common good, would be victorious over most other tribes; and this would be natural selection. At all times throughout the world tribes have supplanted other tribes; and as morality is one important element in their success, the standard of morality and the number of well-endowed men will thus everywhere tend to rise and increase.
In this passage, Darwin clearly demonstrates his awareness that a) moral behaviors are locally disadvantageous or at best deliver no advantage, compared to less moral individuals within the same group, and b) moral behaviors expressed within groups can be decisively advantageous in between-group competition. He didn't comment on the irony that within-group morality might well lead to immoral conduct among groups.
I will return to this issue later, but for the moment let's consolidate our gains. The original problem associated with group selection is foundational for the study of social behavior from an evolutionary perspective. Unlike individual-level adaptations such as the polar bear's thick fur, prosocial behaviors are locally disadvantageous. Fortunately, they are advantageous at the larger scale of whole groups. Prosocial behaviors can evolve by a process of between-group selection, as long as this process is stronger than the opposing process of within-group selection.
Is anyone confused yet? I suspect not. You don't need to be an Einstein to get the basics of group selection. All of us can appreciate that doing the right thing makes us vulnerable to exploitation. We can equally appreciate that united we stand, divided we fall. Why should such simple ideas become the basis of endless controversy?
Yet, as we proceed, I guarantee that you will become confused. One reason that a truth and reconciliation process is needed for group selection is to return to the simplicity of the original problem and Darwin's solution. As Ed Wilson and I put it in our recent review article titled "Rethinking the Theoretical Foundation of Sociobiology": Selfishness beats altruism within groups. Altruistic groups beat selfish groups. Everything else is commentary.
To be continued.