There isn’t much question that our moral instincts —beginning with empathy—are a product of evolution by natural selection. Here’s how it works:
Every living organism has self-replicating material called DNA that determines its physical characteristics. Occasionally the DNA in an organism spontaneously mutates in a way that causes changes in its offspring which are harmful, neutral, or helpful. If the change is harmful, the offspring is less likely to survive to reproduce, so the mutation eventually dies out. If the change is helpful, however, the offspring thrive and reproduce more offspring, and the mutation spreads. Eventually, over long periods of time, the mutant and non-mutant forms of the original organism separate into different species, which is why after millions of years there are so many varieties of life on this planet, from single-celled bacteria all the way up to us incredibly complicated human beings.
I’m no evolutionary anthropologist, but when it comes to morality, I think the most important DNA mutation of all time must be the one that separated the first of us mammals from our reptilian ancestors. After all, while reptilian brains work just fine when it comes to managing hunger, temperature control, fight-or-flight fear responses, reproduction, and the other basics of survival, they have no capacity for memory or emotion. We mammals, on the other hand, have added to those reptilian instincts what biologists call the limbic system, which enables us to feel emotions, remember experiences, and cooperate with one another as a survival strategy. Because more complicated brains take longer to fully develop, however, mammals can’t take care of themselves at birth, and therefore must be nurtured by their mothers. That is where empathy begins, evolutionarily speaking, with the natural selection of those first females who noticed when their offspring were cold, hungry, or endangered, and responded to their needs in ways that kept them alive.
Evidence for the evolution of maternal empathy—which quickly spreads to other relationships—appears in our heads, where our brains produce and process the oxytocin, endorphins, and other hormones associated with cooperative relationships. It also appears in the interactions of the chimpanzees and bonobos studied by primatologist Frans de Waal, who points out that human beings are not the only animals that love, fear, share with, steal from, hold grudges against, forgive, miss, and ultimately grieve one another. On the contrary, many social animals live in highly structured groups where rules and inhibitions, competition and cooperation, and petty selfishness and acts of genuine kindness are everyday realities. What emerges in such groups is the most basic rule of every moral code: Behaviors that cause the group to thrive are rewarded with food, sex, status, or some other benefit, while behaviors that harm the group are punished with violence or shunning, or some other immediate penalty.
What sets us human beings apart, de Wall suggests, is the later development of an additional part of our brain, the pre-frontal cortex, where we reason, think logically, recognize the passage of time, generalize our experiences, and make complex decisions. Our prefrontal cortexes are what enable us to extend primitive moral intuitions into universal standards of behavior—like the Golden Rule—and combine them with increasingly elaborate systems of justification, monitoring, and punishment. That’s where religion comes in, of course, when a group gets too big to reinforce its values the old-fashioned way, and must invent powerful supernatural enforcers with eyes in the sky to deep us in line.
As de Waal put it in his The Bonobo and the Atheist: In Search of Humanism Among the Primates (2013), “It wasn’t God who introduced us to morality; rather, it was the other way around. God was put into place to help us live the way we felt we ought to.”
–Bart Campolo, former evangelical Christian evangelist, now a secular humanist, in his book, Why I Left, Why I Stayed, pp. 110-112