Love and rationality continue to exist because of their survival value. Presumably they, or their antecedents, occurred randomly in a population. Those who loved and cherished and protected tended to maintain their mating relationships and bring their progeny to maturity. The survival value of rationality needs no comment. It is doubtless what has brought us alive from the African plains. The taming of fire, the chipping of a knife, the construction of a wheel, the planting of barley, the catching of wild oxen, the making of laws, it is such things which distinguish us from the grosser brutes. We have an unusual brain. It thinks more deeply, more clearly, more frequently than those of our phylogenetic brethren. It can make an ax which will protect us from the cave bear; it can also construct a bomb with which we may destroy a planet, our own.

The survival value of a property, of course, is a function of its capacity to prolong the survival either of an individual or a group of individuals. There is a substantial correlation, of course, between these two capacities, but the capacities are not identical. The distinction may be clearly drawn in the context of an example. Let us suppose we have two individuals facing a danger. If each is courageous and loyal to the other, let us suppose the danger may be surmounted. Thus, courage and loyalty, in this context, have group survival value, and within the group, individual survival value. On the other hand, let us suppose that one individual turns and runs, and survives, and his fellow is slain. In this situation, courage and loyalty, on the part of the slain individual, did not have survival value. Cowardice on the part of the other did have survival value. He survived. Similarly let us suppose that a given group is attacked. Some refuse to fight, letting others be killed. This obviously has survival value for them. On the other hand, if everyone in the group took the same position, all might fail to survive. The survival value of traits is complex and context-related. A trait which might have negative survival value in one context, say, cowardice, might have positive survival value in another. Similarly a trait which might have positive survival value in one context, courage, might have negative survival value in another. The most courageous individuals, taking perhaps the most risks, might be the most killed.

Survival, essentially, is neutral with respect to what we think of as morality. In certain situations, probably the most selfish, avaricious, and cruel individuals would survive, those that are hardest and least sentimental; in other situations, perhaps such as that of our current world, such properties might be an invitation to extinction. The Bengal tiger has not survived because of his moral qualities. On the other hand, the Bengal tiger is not doing too well today. He might not survive at all if laws were not passed to protect him.