I can't prove it, but I am pretty sure that people gain a selective advantage from believing in things they can't prove. I am dead serious about this. People who are sometimes consumed by false beliefs do better than those who insist on evidence before they believe and act. People who are sometimes swept away by emotions do better in life than those who calculate every move. These advantages have, I believe, shaped mental capacities for intense emotion and passionate beliefs because they give a selective advantage in certain situations.
I am not advocating for irrationality or extreme emotionality. Many, perhaps even most problems of individuals and groups arise from actions based on passion. The Greek initiators and Enlightenment implementers recognized correctly that the world would be better off if reason displaced superstition and crude emotion. I have no interest in going back on that road and fundamentalism remains a severe threat to enlightened civilization. I am arguing, however, that if we want to understand these tendencies we need to quit dismissing them as defects and start considering how they came to exist.
I came to this belief from seeing psychiatric patients while studying game theory and evolutionary biology. Many patients are consumed by fears, sadness, and other emotions they find painful and senseless. Others are crippled by grandiose fantasies or bizarre beliefs. On the other side are those with obsessive compulsive personality. They do not have obsessive compulsive disorder; they do not wash and count all day. They have obsessive compulsive personality characterized by hyper-rationality. They are mystified by other people's emotional outbursts. They do their duty and expect others will too. They are often disappointed in this, giving rise to frequent resentment if not anger. They trade favors according to the rules, and they can't fathom genuine generosity or spiteful hatred.
People who lack passions suffer several disadvantages. When social life results in situations that can be mapped onto game theory, regular predictable behavior is a strategy inferior to allocating actions randomly among the options. The angry person who might seek spiteful revenge is a force to be reckoned with, while a sensible opponent can be easily dealt with. The passionate lover sweeps away a superior but all too practical offer of marriage.
It is harder to explain the disadvantages suffered by people who lack a capacity for faith, but consider the outcomes for those who wait for proof before acting, compared to the those who act on confident conviction. The great things in life are done by people who go ahead when it seems senseless to others. Usually they fail, but sometimes they succeed.
Like nearly every other trait, tendencies for passionate emotions and irrational convictions are most advantageous in some middle range. The optimum for modern life seems to me to be quite a ways towards the rational side of the median, but there are advantages and disadvantages at every point along the spectrum. Making human life better requires that we understand these capacities, and to do that we must seek their origins and functions. I cannot prove this is true, but I believe it is. This belief spurs my search for evidence which will either strengthen my conviction or, if I can discipline my mind sufficiently, convince me that it is false.