Are humans rational?

JDN 2456928 PDT 11:21.

The central point of contention between cognitive economists and neoclassical economists hinges upon the word “rational”: Are humans rational? What do we mean by “rational”?

Neoclassicists are very keen to insist that they think humans are rational, and often characterize the cognitivist view as saying that humans are irrational. (Daniel Ariely has a habit of feeding this view, titling books things like Predictably Irrational and The Upside of Irrationality.) But I really don’t think this is the right way to characterize the difference.

Daniel Kahneman has a somewhat better formulation (from Thinking, Fast and Slow): “I often cringe when my work is credited as demonstrating that human choices are irrational, when in fact our research only shows that Humans are not well described by the rational-agent model.” (Yes, he capitalizes the word “Humans” throughout, which is annoying; but in general it is a great book.)

The problem is that saying “humans are irrational” has the connotation of a universal statement; it seems to be saying that everything we do, all the time, is always and everywhere utterly irrational. And this of course could hardly be further from the truth; we would not have even survived in the savannah, let alone invented the Internet, if we were that irrational. If we simply lurched about randomly without any concept of goals or response to information in the environment, we would have starved to death millions of years ago.

But at the same time, the neoclassical definition of “rational” obviously does not describe human beings. We aren’t infinite identical psychopaths. Particularly bizarre (and frustrating) is the continued insistence that rationality entails selfishness; apparently economists are getting all their philosophy from Ayn Rand (who barely even qualifies as such), rather than the greats such as Immanuel Kant and John Stuart Mill or even the best contemporary philosophers such as Thomas Pogge and John Rawls. All of these latter would be baffled by the notion that selfless compassion is irrational.

Indeed, Kant argued that rationality implies altruism, that a truly coherent worldview requires assent to universal principles that are morally binding on yourself and every other rational being in the universe. (I am not entirely sure he is correct on this point, and in any case it is clear to me that neither you nor I are anywhere near advanced enough beings to seriously attempt such a worldview. Where neoclassicists envision infinite identical psychopaths, Kant envisions infinite identical altruists. In reality we are finite diverse tribalists.)

But even if you drop selfishness, the requirements of perfect information and expected utility maximization are still far too strong to apply to real human beings. If that’s your standard for rationality, then indeed humans—like all beings in the real world—are irrational.

The confusion, I think, comes from the huge gap between ideal rationality and total irrationality. Our behavior is neither perfectly optimal nor hopelessly random, but somewhere in between.

In fact, we are much closer to the side of perfect rationality! Our brains are limited, so they operate according to heuristics: simplified, approximate rules that are correct most of the time. Clever experiments—or complex environments very different from how we evolved—can cause those heuristics to fail, but we must not forget that the reason we have them is that they work extremely well in most cases in the environment in which we evolved. We are about 90% rational—but woe betide that other 10%.

The most obvious example is phobias: Why are people all over the world afraid of snakes, spiders, falling, and drowning? Because those used to be leading causes of death. In the African savannah 200,000 years ago, you weren’t going to be hit by a car, shot with a rifle bullet or poisoned by carbon monoxide. (You’d probably die of malaria, actually; for that one, instead of evolving to be afraid of mosquitoes we evolved a biological defense mechanism—sickle-cell red blood cells.) Death in general was actually much more likely then, particularly for children.

A similar case can be made for other heuristics we use: We are tribal because the proper functioning of our 100-person tribe used to be the most important factor in our survival. We are racist because people physically different from us were usually part of rival tribes and hence potential enemies. We hoard resources even when our technology allows abundance, because a million years ago no such abundance was possible and every meal might be our last.

When asked how common something is, we don’t calculate a posterior probability based upon Bayesian inference—that’s hard. Instead we try to think of examples—that’s easy. That’s the availability heuristic. And if we didn’t have mass media constantly giving us examples of rare events we wouldn’t otherwise have known about, the availability heuristic would actually be quite accurate. Right now, people think of terrorism as common (even though it’s astoundingly rare) because it’s always all over the news; but if you imagine living in an ancient tribe—or even an medieval village!—anything you heard about that often would almost certainly be something actually worth worrying about. Our level of panic over Ebola is totally disproportionate; but in the 14th century that same level of panic about the Black Death would be entirely justified.

When we want to know whether something is a member of a category, again we don’t try to calculate the actual probability; instead we think about how well it seems to fit a model we have of the paradigmatic example of that category—the representativeness heuristic. You see a Black man on a street corner in New York City at night; how likely is it that he will mug you? Pretty small actually, because there were less than 200,000 crimes in all of New York City last year in a city of 8,000,000 people—meaning the probability any given person committed a crime in the previous year was only 2.5%; the probability on any given day would then be less than 0.01%. Maybe having those attributes raises the probability somewhat, but you can still be about 99% sure that this guy isn’t going to mug you tonight. But since he seemed representative of the category in your mind “criminals”, your mind didn’t bother asking how many criminals there are in the first place—an effect called base rate neglect. Even 200 years ago—let alone 1 million—you didn’t have these sorts of reliable statistics, so what else would you use? You basically had no choice but to assess based upon representative traits.

As you probably know, people have trouble dealing with big numbers, and this is a problem in our modern economy where we actually need to keep track of millions or billions or even trillions of dollars moving around. And really I shouldn’t say it that way, because $1 million ($1,000,000) is an amount of money an upper-middle class person could have in a retirement fund, while $1 billion ($1,000,000,000) would make you in the top 1000 richest people in the world, and $1 trillion ($1,000,000,000,000) is enough to end world hunger for at least the next 15 years (it would only take about $1.5 trillion to do it forever, by paying only the interest on the endowment). It’s important to keep this in mind, because otherwise the natural tendency of the human mind is to say “big number” and ignore these enormous differences—it’s called scope neglect. But how often do you really deal with numbers that big? In ancient times, never. Even in the 21st century, not very often. You’ll probably never have $1 billion, and even $1 million is a stretch—so it seems a bit odd to say that you’re irrational if you can’t tell the difference. I guess technically you are, but it’s an error that is unlikely to come up in your daily life.

Where it does come up, of course, is when we’re talking about national or global economic policy. Voters in the United States today have a level of power that for 99.99% of human existence no ordinary person has had. 2 million years ago you may have had a vote in your tribe, but your tribe was only 100 people. 2,000 years ago you may have had a vote in your village, but your village was only 1,000 people. Now you have a vote on the policies of a nation of 300 million people, and more than that really: As goes America, so goes the world. Our economic, cultural, and military hegemony is so total that decisions made by the United States reverberate through the entire human population. We have choices to make about war, trade, and ecology on a far larger scale than our ancestors could have imagined. As a result, the heuristics that served us well millennia ago are now beginning to cause serious problems.

[As an aside: This is why the “Downs Paradox” is so silly. If you’re calculating the marginal utility of your vote purely in terms of its effect on you—you are a psychopath—then yes, it would be irrational for you to vote. And really, by all means: psychopaths, feel free not to vote. But the effect of your vote is much larger than that; in a nation of N people, the decision will potentially affect N people. Your vote contributes 1/N to a decision that affects N people, making the marginal utility of your vote equal to N*1/N = 1. It’s constant. It doesn’t matter how big the nation is, the value of your vote will be exactly the same. The fact that your vote has a small impact on the decision is exactly balanced by the fact that the decision, once made, will have such a large effect on the world. Indeed, since larger nations also influence other nations, the marginal effect of your vote is probably larger in large elections, which means that people are being entirely rational when they go to greater lengths to elect the President of the United States (58% turnout) rather than the Wayne County Commission (18% turnout).]

So that’s the problem. That’s why we have economic crises, why climate change is getting so bad, why we haven’t ended world hunger. It’s not that we’re complete idiots bumbling around with no idea what we’re doing. We simply aren’t optimized for the new environment that has been recently thrust upon us. We are forced to deal with complex problems unlike anything our brains evolved to handle. The truly amazing part is actually that we can solve these problems at all; most lifeforms on Earth simply aren’t mentally flexible enough to do that. Humans found a really neat trick (actually in a formal evolutionary sense a goodtrick, which we know because it also evolved in cephalopods): Our brains have high plasticity, meaning they are capable of adapting themselves to their environment in real-time. Unfortunately this process is difficult and costly; it’s much easier to fall back on our old heuristics. We ask ourselves: Why spend 10 times the effort to make it work 99% of the time when you can make it work 90% of the time so much easier?

Why? Because it’s so incredibly important that we get these things right.


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