From The Simpsons and Family Guy to South Park and 30 Rock, moral dilemmas on TV are often illustrated with the use of a little angel and devil sitting on opposite shoulders. The angel whispers the virtuous thing to do (e.g. “Leave the last donut for someone else to enjoy”), and the devil whispers the opposite (e.g. “Eat the last donut”). But this isn’t just a comedic trope; our brains actually encounter this struggle when we face moral dilemmas. We’re genetically wired that way. There’s a part of us that wants to do what’s good for others (i.e. altruism), and a part that just wants to be selfish. But why? If we all evolved by natural selection (aka survival of the fittest) why are we ever altruistic at all? Shouldn’t we all be eternally selfish for the sake of survival? Is altruism evidence of a soul? Not necessarily. Altruism can be explained by evolutionary theory, and it’s a part of what makes us who we are.
Darwin’s classic theory of evolution, natural selection, paints a bleak picture of life (see The Wire, HBO). Life is simply a struggle to survive and reproduce. The individuals who are best suited to their environment survive and mate and thus pass on their genes and become immortal. Everyone else is just a chump.
It’s easy to see how survival of the fittest can select for selfishness. If I horde food and don’t share with anyone except my immediate family, that’s better for me and my genes. If I’m out hunting in a group and another hunter gets gored by a buffalo, great! More women for me. I should lie, cheat, and steal, anything to get ahead. And we certainly see those features of human behavior. But we also see people helping out their friends with whom they share no genes. We see people helping complete strangers, and giving to charity. Shouldn’t evolution have made us all selfish, just out for ourselves? How does altruism fit in?
The evolutionary biologist E.O. Wilson offers an explanation in his book The Social Conquest of Earth. He points out that a key change in our evolution happened when we started living in groups. In groups, genes that promote positive social behavior like empathy and communication (i.e. pro-social genes) are more advantageous. Natural selection states that genes that are advantageous tend to propagate throughout a population. So pro-social genes began to spread.
First off, lots of animals live in groups. Zebras live in groups because there’s safety in numbers. Lions live in groups because it can be advantageous to hunt cooperatively. But humans have a much more integrated social structure, what Wilson calls “eusocial”, meaning “truly social”. We don’t just live near each other, and hunt with each other. Not only can we work cooperatively, we divide up labor and help look after other people’s kids. We care for the sick and elderly. Our social structure is unique among mammals. It’s most closely related to ants or bees.
For a longer explanation of why this is the case you can read Wilson’s book, but basically once we started using tools and fire we started having campsites to have somewhere to leave all that stuff. Also, since our brains were slowly evolving bigger and bigger that meant our babies’ brains took a long time develop, leaving them defenseless for years. Thus it also became helpful to have a safe place to leave the babies. So we started to have a greater division of labor, leaving all the babies together to be taken care of, and having others going off to hunt. Thus our social structure became more complex as we became more interdependent on each other.
As human social structure became more and more intertwined we began to experience a new evolutionary force: natural selection at the group level. Natural selection at the group level means that the fittest group is most likely to survive and pass on their genes. Imagine two tribes of early humans that lived near each other. One had more pro-social genes, and they worked together better to take care of kids and hunt for food. The other tribe lived together, but everyone was just out for themselves. After a few generations the pro-social tribe is going to thrive and out compete the selfish group for scarce resources. The pro-social tribe is going to survive and reproduce, and the antisocial tribe is going to die off. Hence we’re the descendants of the pro-social tribe.
However, just because we started evolving based on group fitness doesn’t mean we stopped evolving on individual fitness. The absolute best position for passing on your genes would be as the one selfish person in an altruistic tribe. For example, it’s good for the group for people to share their food with each other, but it’s not good for me if I don’t have enough to eat. It’s good for the group to have someone do the dangerous task of hunting, but it’s not good for me if I get hurt or die in the process. It’s good for the group to have tightly knit parents to look after their children, but if I could seduce everyone else’s mate then that’s better for me and my genes. Because advantageous genes tend to spread though a population, if a group is too altruistic, then generation after generation the selfish ones would reproduce more.
The interesting thing is that over the thousands of generations we began to achieve a balance between genes that promote altruism and empathy, and genes that promote selfishness. Groups that were too selfish couldn’t compete with the pro-social, altruistic groups that helped each other out. On the other hand groups that were too altruistic would slowly get taken over by the few individuals among them who were more selfish.
So for the past few million years we’ve been evolving in two ways at once. Group natural selection gave us some pro-social genes that help us work well in groups. At the same time individual natural selection gave us selfish genes that try to get us to the top of the social ladder.
We even see this in the brain networks that control our ability to understand other people (see my last post). In my last post I discussed how we can understand people’s intentions using the dorsomedial prefrontal cortex (DMPFC). The DMPFC is closely tied with the emotional limbic system and helps mediate empathy and other pro-social behaviors. However, there’s another part of the prefrontal cortex, just a little to the side, called the dorsolateral prefrontal cortex (DLPFC). The DLPFC is unemotional and calculating. It allows us to understand and predict other people actions, without getting wrapped up in all the emotion.
One cool experiment that demonstrates this used magnetic pulses to disrupt the DLPFC (Kalbe 2010). The results showed that disrupting the DLPFC messed up thinking but not feeling about other people. That’s because the DLPFC was disrupted, but the DMPFC wasn’t affected. While the DMPFC helps create empathy and understanding and brings people together, the DLPFC allows for scheming and manipulating your way to the top. These distinct brain systems are the product of the opposing evolutionary forces that shaped us.
While our social structure is most similar to ants and bees, they don’t have the same problems as us because they have no individual identity. Being torn between selfishness and altruism is a trait that makes us uniquely human. So next time you have a moral crisis at work deciding whether or not to eat the last donut in the break room, hopefully you can appreciate the millions of years of evolution that led you to that point. The future of the human race rests on you. Choose wisely.
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