Einstein supposedly said: “Two things are infinite: the universe and human stupidity; and I'm not sure about the universe.” In contrast, philosophers such as Aristotle and Donald Davidson have maintained that humans are inherently rational. Moreover, some evolutionary psychologists and Bayesian modelers assume that human thinking is optimal. Thanks to natural selection, our species has arrived at brain processes that just couldn’t get any better.

On the contrary, Gary Marcus in his book Kluge argues that the human mind is just a haphazard construction, put together by an evolutionary process that provides no guarantees of optimality. A kluge is a clumsy or inelegant but sometimes effective solution to a problem. Many evolutionary biologists have pointed out that natural selection only produces organisms that are good enough to survive and reproduce, with no guarantee of optimality. For these purposes, kluges can suffice.

Marcus provides a concise survey of many mental functions that rely on kluges, quirks, and idiosyncrasies rather than optimal processes. Our memories are prone to distortion, conflation and simple failure, in contrast to computers whose memories can store inputs with unlimited accuracy. Human memory is driven by contextual cues, which sometimes works well but can also be easily confused, for example when you’re trying to remember what you had for breakfast yesterday. Memories often blur together, and experiments have shown that it’s easy to implant false memories in people in cases of eyewitness testimony. Even when memory gets it right about what happened, it has difficulty matching this with when it happened.

If thinking were optimal, then people would be extraordinarily good at forming beliefs that are both true and useful. But many psychological experiments show that beliefs and judgments can easily be contaminated by irrelevant information. Distortions and belief formation include anchoring and adjustment, the familiarity effect, confirmation bias, and motivated inference. Humans have to be good enough at forming beliefs to survive and reproduce, but that does not require anything near what is optimal in an increasingly complicated and rapidly changing world.

Many economists and even some political scientists still assume that people make rational choices, performing optimal decision making. But experiments and everyday observations demonstrate numerous irrationalities in human decisions. People make different choices depending on whether a situation is described in terms of gains or losses, even though the payoffs are the same. People are prone to stick with bad situations because their emotions fixate them on sunk costs instead of just thinking about the future. Decision makers end up desperately indebted because of their susceptibility to advertising that leads to impulsive purchases that they cannot afford. People are very bad at dealing with uncertainty, especially when it concerns the far off future, leading to frequent failures to save for retirement and old age.

Human language is far from optimal as it is riddled with idiosyncrasies, ambiguities, redundancies, and vagueness. Language often serves well enough for communication, but also lends itself to misinterpretations and conflicts.

The brain contains neural mechanisms for appreciating and pursuing happiness, but often these do not work very well. Many people end up depressed for long periods of their lives. People often pursue such practices as alcohol, drugs, procrastination, and bad relationships that make them less rather than more happy. These failures are consistent with the view of evolution as leading to pretty good capacities, but contrary to the assumption that it has generated optimal brains.

So philosophy and psychology should abandon assumptions that human minds are in any way optimal or rational, and instead concentrate on two crucial questions. First, how do brains actually work, that is what are the neural mechanisms that make us good but imperfect at remembering, belief formation, decision-making, language, and the pursuit of happiness? Second, how can we use what is known about psychology, scientific method, and critical thinking to help people to reason better? Fortunately, human cultural developments over the last few thousand years have given us many ways to improve on our spotty evolutionary legacy. We don't have to be dumb and dumberer if we work at it.   

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