Is killing part of human nature?

© iStockphoto.com/Thinkstock

William Shakespeare's Hamlet proclaimed, "What a piece of work is a man, how noble in reason, how infinite in faculties, in form and moving how express and admirable, in action how like an angel, in apprehension how like a god!" Hamlet's point was that humans are a remarkable species -- though Hamlet himself has lost all appreciation for mankind. Humans have created phenomenal architectural structures ranging from pyramids to skyscrapers. We've explored the depths of the ocean and the surface of the moon. We've created works of art that can affect emotions and provoke thoughtful conversations.

Perhaps what makes us even more remarkable is that we have this seemingly infinite capacity to achieve great things, and yet our history is filled with violence toward one another. How can we dedicate countless hours to matters of art, science, and other sophisticated pursuits and still commit acts of murder or wage globe-spanning wars?

We have a tendency to think of ourselves as existing apart from other species. Humans have the ability to reason and pass down knowledge to future generations. This ability makes it seem like we base our actions mainly upon rationality. But how do we reconcile that with the act of eliminating other members of our own species?

It's a complex problem. Part of the answer may be that we're not as separate from other animals as we imagine. It's dangerous to ascribe traits to other species -- we run the risk of anthropomorphizing animals and assuming the reasons they behave a certain way are the same as our own. But in general, it seems that animal behavior is the product of instinct, emotion and reason. Some animals demonstrate a greater aptitude for reasoning than others. Humans are at the top of that list.

But that doesn't mean all our decisions are based upon cold, calculating rationality. Neuroscientist Antonio Damasio's research indicates that emotions play an important role in decision making. He conducted experiments with people who had suffered brain damage that affected the part of the brain that allows us to experience emotions. In his studies, Damasio found that the patients had trouble making choices. They could identify solutions to a problem but couldn't decide upon a specific course of action [source: Wrangham and Peterson].

Why is that important? It indicates that while we're not slaves to our emotions, they play an important part in how we behave. Next, we'll look at how genetics, the environment and our emotions can turn a person into a killer.