randombio.com | science commentary
Saturday, January 06, 2018

Instinct and behavior

The defining characteristic of instinct is that we don't know we have it. But we can't understand human behavior without it.


P hilosophers tell us we can never be sure that reason is telling us the true nature of the world. The brain does not care whether what it tells us is true. That's not its function. Its sole purpose is the one that's shared with every other organ, every cell, and every molecule in the body: to ensure the survival of the species.

There was an old sci-fi movie where the inhabitants of a space station are being infiltrated by terrible, hideous creatures that have the power to make humans see them as long-lost friends. Only the commander, who is delirious with a fever, and therefore relieved of the obligation to accede to social norms, saw their true appearance. That movie hit on a profound truth: most of the time, our programming is invisible to us.

The brain creates a narrative that is designed to make us feel happy and to trick us into reproducing. This makes is uniquely susceptible to falsehoods that play upon that goal. The result is that when unexpected things happen, like wars, economic crises, and the election to high office of strange orange beings, they seem inexplicable.

We all know that animals are pre-programmed with knowledge and instinctual behavior. But humans have it as well. There's good evidence that our fear of snakes may be instinctual.

In the popular imagination, fear of the dark and fear of heights are also instinctual. But it's unclear whether these are truly innate fears: baby humans seem perversely attracted to stairways, and children learn very quickly that darkness can be dangerous. Likewise our fear of dirt and blood are probably mostly learned, as is our fear of fire and our fear of death.

Risk-taking and novelty-seeking behavior are probably not instincts, either. They're more like general physiological tendencies, where the brain tries to avoid boredom and pain and seeks physiological arousal.

Graph of male-female inequality across 107 countries
Fig. 1 Correlations between various measures of male-female inequality and fertility rate across 107 countries. Fertility rates data SIGI Index data

True instincts are behavior patterns that manifest themselves without our knowledge. One area where there's good reason to think that instinct may be important is in human reproduction.

Males and females test each other to determine their suitability as a mate. Females issue challenges to the male, sometimes subtle, and sometimes overt. They're constantly testing males: Can you open this jar? Here's an puzzle I found, isn't it interesting, can you solve it? Will you please put the seat down? Can you fix my tire? They don't realize what they're doing because it's instinctive. If the male doesn't defeat the challenge, the female resigns herself to failure or moves on to the next one.

Despite what they may say in a formal survey, an inheritance—genetic as much as physical—is what women really want, and they'll tear society apart to get it. Not because they hate society, but because that is what nature programmed them to do. Most of the time, they don't realize they're doing it. It's instinctual behavior and therefore unconscious.

Probably the least understood factor in human behavior is how fertility rates are determined. I down­loaded these numbers (Fig. 1) a few months ago, and I've been puzzling over them ever since. They show that fertility rates correlate strongly with sex inequality. There is no correlation with son bias. But there's a very strong correlation, p=2×10−20, with restricted physical integrity value.

This means that, for whatever reason, when women are oppressed and prevented from traveling on their own, birth rates increase.

There are, or course, conventional explanations for it: poverty, education, boredom, lack of access to contraception, or social conditions. But these explanations don't tell us much—they are ‘just-so’ arguments that could just as easily explain the opposite result.* The graphs also don't tell us whether one extreme is objectively better than another, or whether we should strive to increase or decrease fertility rates. And they certainly don't tell us how men should treat women. What they tell us is that there are instinctual behaviors at work that we don't understand. If the survival of humans is related to fertility—and that seems indisputable—we need to start understanding it and stop pretending that it's all just a function of inequality and political power.

These graphs, it seems to me, are strong evidence for a role of instinct in an important aspect of human behavior, and this makes the phenomenon worth studying.

No doubt some people will resist the idea. We want to believe that all our behavior is purely rational. But if we're unaware of basic facts of human biology, we will experience weird problems that seem to come out of nowhere. Without understanding their causes, we'll apply the wrong solution. And, as with passing new laws to fix the problems with old laws, it will only create new problems.


* You could argue, for instance, that people in rich countries should have higher fertility rates because they have better education on modern techniques to ensure survival of the fetus, and they have better nutrition which reduces difficulty conceiving and prevents low baby birthweight, and that political security leads to boredom, while insecurity just causes stress. There is scientific support for each of these arguments, and in fact they were used to explain earlier baby booms in Western countries.


jan 06 2018, 4:53 am. exponent fixed jan 06; revised jan 07, 5:01 am. last edited jan 07, 2018, 7:03 am

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