Originally Posted by
Khelek
People have fear responses based on their threat assessment of a situation. Evolution has given most people an in-group preference, since mankind has been warring for thousands of years. Racists are either born or conditions to view those outside their group as an extreme threat. Due to low intelligence, the level of threat posed is misconstrued beyond reality.
The converse is also a sign of low intelligence. Some people are, to a greater or lesser extent, completely blind to real threats. Interestingly, modern brain scanning techniques have yielded some intriguing results. Through stimulation of certain parts of the brain, people can become less religious and more open to others different from themselves and conversely they can be made more cautions and timid in their interactions with others.
Human evolution has walked a fine balance between the benefits of social interaction in the form of trade and cooperation and the risk of exposing oneself and their family/tribe to violence or to being taken advantage of.
I'll quote the sage Greg House, M.D.
Three cavemen see a stranger running towards them with a spear. One fights, one flees, one smiles and invites him over for fondue. That last guy didn't last long enough to procreate.