The Rational Animal: How Evolution Made Us Smarter Than We Think (14 page)

Natural selection creates systems, like the brain, that are biased to minimize the costlier error.
This built-in bias to avoid evolutionarily expensive errors is known as the
smoke detector principle
.
Evolutionary psychologists Martie Haselton and Randy Nesse believe that natural
selection engineered human judgment and decision making to be biased according to the same principle.
Like a good smoke detector, our brain is rigged to sound the alarm even when there is no fire, forcing us to tolerate the inconvenience of false alarms to avoid potentially lethal misses.
Because our evolutionary tendencies steer us toward avoiding costly errors, our decisions will result in more small errors.
But we are disposed to produce little errors so that we avoid big mistakes.

MONEY UP IN SMOKE

The smoke detector principle underlies a plethora of decision errors, such as when you expend the extra effort to put on your seat belt, then don’t get in an accident.
The decision to wear a seat belt produces an error 999 times out of 1,000.
In the overwhelming majority of situations, we drive around strapped into an irritating harness that provides no benefit (it’s akin to lugging around an unwieldy umbrella on a sunny day).
Yet after a few decades of griping, most sensible people now happily choose to commit the seat belt error, and the result has been a dramatic drop in auto fatalities compared to our belt-resisting grandparents’ day.
The smoke detector principle leads people to make this small error to avoid the much costlier mistake of getting into an accident without wearing a seat belt.

The smoke detector perspective on decision errors is radically different from how such errors are normally viewed.
Many economists, for example, argue that people are especially prone to making errors when it comes to money.
Books such as
Why Smart People Make Big Money Mistakes
and
Mean Markets and Lizard Brains
allege that people are foolish financial investors.
They claim that one of the most common money mistakes is that people take too little risk with their financial investments—humans are notoriously risk averse.
Because US stocks have historically outperformed all other types of investments over the long run, many rational types are befuddled that more people are not investing in stocks.
If you have saved up $5,000 and have many years left before retirement, the smart and rational Econ would put this money in a mix of investments that include a fair share of risky stocks.
Instead, many people choose to tuck the $5,000 away
in a bank—where it is likely to earn a piddling interest rate that barely covers the loss due to inflation.
From a traditional economic perspective, this seems irrational.

But think about the same financial decision in light of the smoke detector principle.
The decision about what to do with your $5,000 life-savings account could produce two types of errors.
One possibility is that you put the money in the bank and the stock market booms.
Instead of having a nice return on your investment, you have only your $5,000 plus a measly 1.8 percent interest.
This is the supposedly egregious error that makes risk aversion appear so irrational.

We agree that this is an error, but making this error won’t cost you your shirt and tie (and your life savings).
Consider the other possibility: you invest all your money in stocks, and the market plummets.
Now your life savings are gone.
Indeed, one of us moved a good portion of his retirement funds from low-interest bond accounts into stocks in 2001.
Within a few months of that decision, the stock market took a historically unprecedented dive in value and then another nosedive a short time after that.
As we mentioned in the book’s opening pages, he is now in a position to retire sometime around age seventy-nine or eighty and, even then, may have to live out his golden years in a modest hut somewhere in Ecuador.

The smoke detector principle has preset our brains to be wary of situations in which we could lose our resources, because this is the much costlier error.
The human tendency toward risk aversion may lead to errors, but it is a calculated bias—engineered by natural selection to avoid a much bigger mistake.

DIFFERENT BIASES FOR DIFFERENT SUBSELVES

When are we inclined to be overly conservative in our judgments, and when are we inclined to be more carefree?
It depends on which of our subselves is currently in charge of making judgments and decisions.
Different subselves have different evolutionary goals, and the criteria for what makes a smart decision differ quite drastically depending on whether you’re currently worried about disease as opposed to seeking
a mate or caring for your children.
Let’s go inside the mind of our different subselves to see how this works.

THE BEHAVIORAL IMMUNE SYSTEM: IN THE MIND OF YOUR DISEASE-AVOIDANCE SUBSELF

Think about the last time you sneezed.
Was your body in real danger?
Probably not.
When we sneeze, our body has frequently made an error, because there is no real threat.
Instead, some dander particle or a whiff of chili powder sets off a false alarm.
But we are physiologically wired to sneeze at the slightest of respiratory irritations because our body’s defenses evolved to be safe rather than sorry.

Our immune system is rigged the same way.
An army of white blood cells is ready to go to war if it senses any germ-like substance swimming in our bloodstream.
But sending the entire body to war can be expensive, using up precious bodily resources.
So natural selection endowed us with a crude first line of defense against pathogens—what evolutionary psychologist Mark Schaller calls the
behavioral immune system
.
This psychological system is a set of disease-avoidant thoughts and behaviors operated by our disease-avoidance subself.

The behavioral immune system is a pathogen detector.
Just as smoke detectors are sensitive to anything that could resemble smoke, the behavioral immune system is hypersensitive to anything associated with disease.
The system is triggered by the sight, smell, or sound of people, places, or odors that could signal dangerous pathogens in the vicinity.
Its alarm goes off anytime we’re exposed to unsightly sores on someone’s arm, the scent of decaying meat, or a man coughing on the bus.
When our senses detect something or someone that smells, looks, or sounds strange or different, our disease-avoidance subself makes sure that our behavior changes accordingly.

One study by Josh Tybur and Angela Bryan found that when people were exposed to an unpleasant odor, they were more willing to use condoms.
In this case the pathogen cue was superficial and harmless (a squirt from a gag aerosol with a sulfur dioxide scent reminiscent of flatulence and descriptively named “Liquid Ass”).
Nevertheless, the
harmless stench triggered people’s behavioral inclination to protect themselves from sexually transmitted disease.

The realm of psychology (the behavioral immune system) and the realm of biology (the physical immune system) are often thought of as independent spheres.
But evolution has harnessed both psychology and biology in a brilliantly coordinated, deeply rational system.
As it turns out, activating the behavioral immune system in turn triggers a red alert in the body’s physical immune system, the standing army of T cells and other germ-killing lymphocytes.
Mark Schaller conducted a clever experiment to test just how closely the two systems work together.
He and his team asked people to watch a slide show containing pictures of people who looked sick.
The photos depicted folks with rashes and pox, as well as images of people coughing and sneezing as mucus spewed out of their noses.
Study participants gave blood samples both before and after watching the images.
The researchers then exposed these samples to a bacterial infection to measure the presence of interleukin-6 (IL-6), a pro-inflammatory cytokine that white blood cells make when they detect microbial intruders.
A higher level of IL-6 indicates that the body has begun to mount a more aggressive immune response to infection—it’s the equivalent of the immune system’s troops preparing to go to battle.

By measuring inflammation before and after the slide show, the researchers were able to determine whether seeing pictures of disease-y people actually stimulated the immune system to fight infection—and it did!
Merely seeing images of people who might be sick triggered white blood cells to mount a vigorous response to bacterial infection.
The researchers even found that the immune system was deeply rational about the types of images that set off a biological response.
A different group of participants viewed photos of people who looked dangerous.
Some of the people in these photos brandished guns pointed right at the camera, thus aimed directly at the participants themselves (these kinds of images trigger the self-protection subself).
Although the dangerous pictures were rated as even more distressing than the disease-y pictures, exposure to images of physical danger had no effect on immune system reaction.
Only exposure to disease cues prompted the immune system to kick into higher gear.

REVISITING ZAMBIAN AID AND MUTANT FRENCH FRIES

The behavioral immune system produces an array of responses designed to help prevent infection.
Some of these responses may initially appear irrational and completely unrelated to disease.
For instance, priming the disease-avoidance subself leads people to be more prejudiced against foreigners from exotic places like Sri Lanka and Ethiopia.
While this seems a little strange at first blush, it makes much more sense when one considers that strange outsiders have historically been likely to carry diseases foreign to our immune system, making us especially vulnerable.
Most of the post-Columbus decline in the Native American population was due merely to coming into contact with diseases carried by the Europeans.
The massacre at Wounded Knee was nothing compared to smallpox.
Our psychological disease-avoidance system facilitates deeply rational responses by spurring us to avoid contact with anything or anyone that might require a physiologically costly mobilization of our real immune system.

Given what we know about our behavioral immune system, let’s revisit the Zambian food-aid predicament, in which even hungry people refused to eat genetically modified food.
When people think about eating genetically modified substances, they often imagine ingesting something physically unnatural, strange, and unknown into their bodies.
We want our fruits and vegetables to be “natural.”
Labeling them as “genetically modified” conjures up unnatural science fiction images—a disfigured blue potato or a red banana with lumpy outgrowths.

Aid workers were outraged at the Zambian president for rejecting genetically modified food aid, especially because many Americans were already eating genetically modified foods on a daily basis.
In 2000, around the time of the Zambian aid fiasco, all french fries served in American McDonald’s restaurants came from genetically modified potatoes.
But it turns out that while consumers loved the taste of these super McSpuds, the vast majority were unaware they were eating genetically modified potatoes.

When Americans learned about the true origin of their fries, it sparked a national outrage in the United States not too different from the indignation in Zambia.
American citizens insisted that they would
only eat “normal” potatoes.
It didn’t matter that agricultural inspectors had deemed the genetically modified potatoes perfectly safe.
Nor did it make any difference that the World Health Organization has never found ill effects on human health from eating genetically modified foods.
Cognitive reasoning has little effect on people when the disease-avoidance subself takes charge.
As a result of the protests, McDonald’s had no choice but to switch back to the old “natural” potatoes.
In the same way that Zambians refused to ingest genetically modified food, Americans refused to touch mutant french fries.

SEX DETECTORS: IN THE MIND OF MEN’S MATE-ACQUISITION SUBSELVES

Thus far we have focused on ancestral biases geared for successful defense, such as those used by our disease-avoidance subself that protect us from disease.
But in the game of natural selection, a good defense is only part of the story.
Evolutionary success involves both solving the challenges of danger and disease (having a good defense) and taking advantage of opportunities to make friends, gain status, and reproduce (having a good offense).
In fact, a good offense can be even more critical from an evolutionary perspective.
If a successfully defensive person lives to be one hundred years old, his genes will die with him unless he can send some of them out on a mating mission.
By contrast, the genes of a mediocre defender who only manages to live to age thirty still have a chance as long as he sends some of his genes out on a few successful quests.

Just as animals have detection systems to spot danger and disease, they have other sets of mechanisms to detect opportunities.
Take the silkworm moth, known to fluent Latin entomologists as
Bombyx mori
and to the ancient Chinese as a flying cash crop.
When female silkworm moths are interested in mating, they release a chemical called bombykol.
The evolutionary success of male moths depends on whether they can detect the presence of an interested female.
But there’s a problem: females produce only the tiniest amounts of this sex pheromone.
So males have evolved extremely sensitive bombykol detectors, enabling them to detect this chemical in concentrations as low
as 1 molecule in 1,000,000,000,000,000,000 air molecules (that’s a quintillion, in case your cash supplies don’t typically require you to count that many zeroes).
With that level of sensitivity, a guy moth can detect the scent of a lady moth over ten kilometers away.
When it comes to mating, male silkworm moths are like sharks, which can detect a drop of blood in a bay full of water and dart toward their target.

In the same way that evolution has endowed humans with intentionally biased smoke detectors for superb defense, natural selection has also produced intentionally biased sex detectors for conducting a mating offense.
Unlike the shrill wail of a smoke detector, which leads us to avoid deadly mistakes, the sound of a sex detector alarm is a pleasant melody, propelling us toward reproductive opportunities.
Men, for example, are notorious for making judgment errors when it comes to gauging women’s romantic interest.
As many women can attest, men are often delusional—a guy may think a woman is romantically interested in him when nothing could be further from the truth.
If an attractive woman does so much as look a man’s way, many men think: She wants me.