Are Humans Rational?

How evolution shaped the human mind to only sometimes be logical.

Posted Nov 26, 2019

This is a guest blog written by a member of the SUNY New Paltz Evolutionary Psychology Lab, Alex Mackiel.

PublicDomainPictures - 17913 images / Pixabay
Source: PublicDomainPictures - 17913 images / Pixabay

People hold potentially misguided beliefs for all sorts of reasons. People want to be loyal to the values of their family, friends, political party, or religion. Some want to make a good impression for their boss and potential future employers. Others want to avoid conflict around those with whom they know will disagree. In other words, there are many reasons, some of which are actually rational, as to why we often reason poorly.

Are Humans Rational?

It has seemingly become a pastime of cognitive psychologists to find all the instances in which human reasoning flounders. Experts tell us that humans are poor reasoners. We fail miserably at rather simple conditional logic tasks of the following form: You are presented with four cards each of which has a number on one side and a letter on the other. For example, you are presented with four cards that show 4, 7, E, and K. You are given the following task: Which two cards must you turn over to test the truth of the proposition that if a card shows a vowel on one side then there is an even number on the other side? Take a guess.

The correct answer is that you turn over the card with the E (that’s the easy one) and your turn over the card with the number 7 (huh?). Most people get this wrong. In fact, research shows that less than 10% of people flip over the correct cards (Evans et al., 1993). Most people find themselves flipping the letter E, which is correct and flipping the card with the number 4, which is incorrect.

Moreover, a long list of cognitive biases has been generated showing how we reason differently about two pieces of information which are exactly equal in logic but differ in wording (framing effect), use irrelevant information to color how we understand probability (conjunction fallacy), reason about the rate of something based on how easily we can recall events (availability heuristic), find evidence to confirm our preexisting beliefs (confirmation bias), and much more (Tversky & Kahneman, 1974).

We Don’t Reason Like Computers Do

From the evidence presented thus far, one is prepared to conclude that humans are poor reasoners. Yet what is often conspicuously missing from this literature is the phrase "compared to what?" Compared to computers we are poor reasoners. But that’s always going to be the case since we developed computers to be perfectly logical. The question is, is it reasonable to suppose that humans reason like computers? Were humans designed to be perfectly logical? From an evolutionary perspective, there is little reason to suppose that this is the case.

To use a phrase I’ve heard voiced by cognitive psychologist Steven Pinker, “Reality is a powerful selection pressure.” And so it makes sense that truth and rationality are destinations reasoning minds can sometimes stumble upon. While we are poor reasoners in comparison to computers, compared to nearly all other animal species, our ability to reason is remarkable. We inhibit base impulses and defer and delay present gratification based on future concerns. We model behavioral patterns and sequences of actions in our minds before playing them out in reality. That way we can problem solve without physically suffering the ramifications of failure.

We outsmart every other species because we set goals, plan in advance, think before acting, remember what works and what doesn’t work and update our behavior in light of that information (Pinker, 2010; Tooby & DeVore, 1987).

However, truth and rationality also have unfortunate qualities to them. The truth can ruin someone’s day. It cares little for our feelings, rips off the masks we wear to conceal our vulnerabilities and flaws, penetrates through our petty attempts at infallibility, omniscience, and righteousness to reveal the mere mortal hiding in the corner behind it all. These features of truth and rationality, among others, may have pushed human reasoning off the path of perfect logicality.

We don’t always want the truth. Instead, we often want to convince others of our opinionated hot-take masquerading as truth in order to persuade them to join our cause. We distort the truth to make ourselves and others feel better, look better, and appear to be the godlike beings that we aren’t. We find evidence for, and deny evidence against opinions and beliefs we hold for groups to which we belong and for people with whom we socialize (a fact that will take you much further in understanding climate change denial than scientific ignorance).

Bringing Evolution Into the Picture

The assumptions traditionally underlying the field of reasoning psychology have been that human reasoning functions to enhance individual cognition (Mercier & Sperber, 2011). The field began and still is to a large degree framed within the Aristotelian logical framework that human reason functions to lead us to the logical answer. And so, human reasoning has been mostly assessed using deductive reasoning tasks in the form of syllogisms. But this is most likely not the assumptions on which reasoning evolved, because often the truth is exactly what we want to avoid, and avoiding it could have been evolutionarily advantageous especially for those who were especially good in persuading, deceiving, and arguing themselves out of truth’s crosshairs.

I propose that Aristotle needs to be supplanted with Darwin in this respect. Darwin offered the only theory of how organic design comes into being: evolution by natural selection. And natural selection is the process by which organisms become fitted to the environments in which they evolve. Reasoning is almost certainly an adaptive mental faculty, or set of mental faculties that was selected for through evolutionary time. But reasoning, as I stated above, likely didn’t evolve to enhance individual cognition or lead to truth.

Cognitive scientists Dan Sperber and Hugo Mercier have offered an evolutionarily informed perspective on reasoning as a mental faculty that came about due to adaptations for aiding in human social life, in particular, communication (Mercier & Sperber, 2011). Specifically, for them, the main function of reasoning is argumentative. Its proper function is to devise and evaluate arguments in a communicative context to convince others who would otherwise not accept what one says on the basis of trust.

Indeed, studies show that when reasoning is situated in argumentative contexts, people actually are good reasoners (Mercier & Sperber, 2011). It has been shown that people’s performance solving abstract logical syllogisms increases when these syllogisms are situated in an argumentative context (Mercier & Sperber, 2011; Petty & Wegener, 1998; Thompson et al., 2005).

Additionally, studies in motivated reasoning show that when people are motivated to reject a conclusion (e.g., when that conclusion implies something bad about them) they will use the evidence presented to them to disconfirm the conclusion. However, when people are motivated to accept a conclusion (e.g., when that conclusion implies something good about them) they will discount that very same information (Ditto & Lopez 1992). This argumentative theory of reasoning not only explains the apparent lack of reasoning skills in traditional tasks used to assess reasoning, but also explains key properties of reasoning such as strong differences in producing versus evaluating arguments.

Since reasoning functions to argue one’s case persuasively, this theory predicts that people should be both biased and lazy in the production of arguments. Specifically, they should have a strong confirmation bias in the production of arguments, producing arguments that favor their own point of view and attack that of their opponent. In this sense, confirmation bias is a feature of reasoning rather than a flaw, since it aids in the overall function of reasoning in arguing one’s case. Additionally, people are predicted to be lazy in the production of their arguments, quickly coming up with arguments without anticipating counterarguments (Mercier & Sperber 2011).

On the other hand, however, this theory predicts that when evaluating arguments, especially arguments of an interlocutor with opposing views, rather than being biased and lazy people are demanding and objective. Demanding because they don’t want to be swayed by any counterargument, but objective because they still want to be convinced of strong and truthful arguments, which is the whole point of arguing in the first place.

A number of studies show support for the distinction between the production and evaluation of arguments (Mercier & Sperber, 2011; Mercier & Sperber, 2017). When people reason alone relying on the production of arguments in isolation, they reason poorly. However, when people reason in group dialogic contexts in which arguments are being produced and evaluated people reason very well (Mercier, 2016; Mercier & Sperber, 2011). Additionally, this theory explains many of the seeming gaps in human reasoning such as the confirmation bias, laziness in reasoning, motivated reasoning, and the phenomenon of justification and rationalization in reasoning tasks (Gigerenzer, 2018; Mercier & Sperber, 2017).

As far as we know, the human brain is the most intricate and complex thing that exists in the universe. The list of “biases” and so-called “systematic errors” in our thinking needs to be reexamined in light of Darwinian evolution. In fact, when information is made to better match our intuitions and the conditions in which we evolved, many of these biases begin to look less like errors in cognition and more like errors in theory (Gigerenzer, 2018; Mercier & Sperber, 2017).

Human reason does not function to calculate the right answer like a perfectly logical computer. All adaptations, including the ones that give rise to human reasoning, have the built-in assumption of leading to increased reproductive fitness, which in the case of reasoning has been proposed to function mainly in human social life. We use reason to improve communication: to give justification for oneself and the ideas we hold, to persuade others of our case, to evaluate one’s reasons on the basis of objectivity, among others. This does not mean that we cannot reason logically like a computer (don’t forget we developed computers!), but just that logic is not the primary function of human reasoning. To understand how something like reasoning works in a biological sense requires that we understand how it evolved, which has implications for what it can and cannot do.

Bird wings are adaptations, and yet they cannot fly in the upper atmosphere where air particles are too far apart; vertebrate eyes are adapted organs which allow organisms to visually perceive the world and yet they cannot perceive radio waves, X-rays, infrared light, or any other kind of light other than the visible spectrum. Similarly, human reasoning has an adaptive function and yet there is little agreement on what functions it evolved to do. Understanding the conditions under which reasoning evolved and its proper function—the function it was designed to solve—will help us to understand reasoning’s actual function—everything reasoning can actually do (Sperber, 1994). A better understanding of this will not only help us in understanding the mechanisms involved in reasoning, but also inform us about which contexts are most suitable to eliciting reasoned arguments. This is deeply important when it comes to policymakers and decision-makers in society, but also for education. What kind of classroom context best enables students to think straight about important topics?

Bottom Line

Fortunately, we already understand many of the ways in which reasoning fails and reasoning is facilitated. For instance, of the various reasons why we should have our writing edited by another person, one is that he or she will raise counterarguments that we failed to anticipate and address by virtue of not knowing what we don’t know. Similarly, when we individually come to a conclusion about a controversial issue it is important to converse with others, especially with those of whom we disagree because they will raise counterarguments that will give much-needed nuance, revision, and ultimately strength to our own arguments. Knowledge is forever provisional, and humans are forever fallible. Therefore, it is important that our reasons, arguments, seemingly settled conclusions and points of view be exposed to continual debate and criticism.

Alex Mackiel is currently a graduate student in Psychological Science and a member of the New Paltz Evolutionary Psychology Lab. He is an alumnus of Carleton College where he majored in both Psychology and English. He has contributed articles related to evolutionary psychology to Quillette on multiple occasions including What Explains the Resistance to Evolutionary Psychology? and Socialization Isn't Responsible for Greater Male Violence. Follow him on Twitter @ajmackiel.


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