One of the fundamental assumptions of is that there is nothing special about the human brain. It is an evolved organ, just like the hand or the pancreas or any other part of the human body.

Just like all the other parts of the human body, the brain – and all the evolved psychological mechanisms in it – are designed for and adapted to the conditions of the ancestral environment in which they evolved, not necessarily to the current environment. This principle holds for both psychological adaptations, like evolved psychological mechanisms, and physical adaptations, like the eye, the vision, and the color recognition system.

What color is a banana? A banana is yellow in the sunlight and in the moonlight. It is yellow on a sunny day, on a cloudy day, on a rainy day. It is yellow at dawn and at dusk. The color of the banana appears constant to the human eye under all these conditions, despite the fact that the actual wavelengths of the light reflected by the surface of the banana under these varied conditions are different. Objectively, they are not the same color all the time. However, the human eye and color recognition system can compensate for these varied conditions because they all occurred during the course of the evolution of the human vision system, and can perceive the objectively varied colors as constantly yellow.

So a banana looks yellow under all conditions, except in a parking lot at night. Under the sodium vapor lights commonly used to illuminate parking lots, a banana does not appear natural yellow. This is because the sodium vapor lights did not exist in the ancestral environment, during the course of the evolution of the human vision system, and the visual cortex is therefore incapable of compensating for them.

Fans of the 1989 James Cameron movie The Abyss may recall a scene toward the end of the movie, where it is impossible for a diver to distinguish colors under artificial lighting in the otherwise total darkness of the deep oceanic basin. Regular viewers of the TV program Files and other real-life shows may further recall that eyewitnesses often misidentify the colors of cars on freeways, leading the police either to rule in or rule out potential suspects incorrectly. Highways and freeways are often lit with sodium vapor lights and other evolutionarily novel sources of illumination.

The same principle that holds for physical adaptations like the color recognition system also holds for psychological adaptations. Pioneers of evolutionary psychology all recognized that the psychological adaptations are designed for and adapted to the conditions of the ancestral environment, not necessarily to the conditions of the current environment. I call these observations the Savanna Principle: The human brain has difficulty comprehending and dealing with entities and situations that did not exist in the ancestral environment. Other evolutionary psychologists call the same observation the evolutionary legacy hypothesis or the mismatch hypothesis.

One example of the Savanna Principle in action is the fact that individuals who watch certain types of TV shows are more satisfied with their friendships, just as they are if they had more friends or socialized with them more frequently. It makes perfect sense that people who have more friends and socialize with them more frequently are more satisfied with their friendships than those who don’t have as many friends or socialize with them as frequently. And they are. What’s interesting is that the same thing happens if they watch more TV. From the perspective of the Savanna Principle, this is probably because realistic images of other humans, such as television, movies, videos, DVDs, and photographs, did not exist in the ancestral environment, where all realistic images of other humans were other humans. As a result, the Savanna Principle suggests that the human brain may have implicit difficulty distinguishing their “TV friends” – the characters they repeatedly see on TV shows – and their real friends.

Another example, discussed extensively in a previous post, is the fact that, when experimental psychologists deliberately create a situation where people earn money when they are ostracized and lose money when they are included, people still feel happy when they are included (and lose money) and hurt when they are excluded (and make money). While this makes no sense from a purely economic perspective, it is perfectly consistent with the Savanna Principle. Throughout the course of human evolution, exclusion from a group was always costly and inclusion was always beneficial. These two factors always covaried throughout evolutionary history, because there were no evil experimental psychologists in the ancestral environment to manipulate them independently. There were no such things as beneficial exclusion or costly inclusion, and the human brain cannot therefore comprehend them. It implicitly assumes that all inclusion is beneficial and all exclusion is costly.

So it appears that the human brain indeed has difficulty comprehending and dealing with entities and situations that did not exist in the ancestral environment, as the Savanna Principle suggests. If you look around, you will realize that virtually nothing in your current environment existed in the ancestral environment. In fact, I believe there are only four entities in our current environment that existed in the ancestral environment: men, women, boys, and girls. If you are outside, you may be tempted to include such natural features as trees, mountains, and rivers, but unless you are on the African savanna, they are not the same trees, mountains, and rivers that existed in the ancestral environment. There are more situations and relationships in your current environment that still existed in the ancestral environment, such as friendships, alliances, and (“ ”). But many of these situations and relationships today involve evolutionarily novel components (Facebook, written contracts enforceable by government, marriage certificates).

The key word in the Savanna Principle – The human brain has difficulty comprehending and dealing with entities and situations that did not exist in the ancestral environment – is difficulty, not impossibility. It is sometimes possible to overcome the limitations of the human brain consciously – it is possible for us to remember that the characters we see on TV are professional actors who are paid millions of dollars to play scripted roles – but it is often difficult. Even when we are aware of something at the conscious level, we still act as if we weren’t, as when we become more satisfied with our friendships when we watch more TV. The observation captured in the Savanna Principle has very powerful and profound implications for evolutionary psychology and how the human brain functions.