Is this the end of personal responsibility?

If identical twins were more similar than non-identical twins, then there was some genetic role; but if they were less than twice as similar, then there was some role for the “shared environment”. The shared environment is all that stuff that siblings go through together: parenting, schooling, neighbourhood, the stuff we think of when we think of “nurture”. Everything that’s not genetics or shared environment is known as “non-shared environment”, a technical term that essentially means “random stuff”.

The finding was that the average correlation among identical twins was 0.58 (on a scale of -1 to 1), while the correlation among non-identical twins was 0.28. That is: the study found that about 60% of the variation in our ability to control our impulses is genetic. And the identical twins’ score was twice that of the non-identical ones, so the shared environment seems to have “little influence”. It appears to be essentially genes plus random stuff.

This isn’t the final word; for one thing, the paper hasn’t been through peer review yet. For another, no one study, even a meta-analysis, is unvarnished truth. But it’s in line with expectations.

And it’s worth thinking through the implications. We criticise people for laziness, but laziness is a manifestation of poor self-control; an inability to overcome the urge to do nothing. People with low impulse control find it harder to resist psychoactive substances – drink, drugs, tobacco – and to resist high-calorie foods. They also may struggle to resist violent or aggressive impulses, and be more likely to face trouble with the law.

People look at this the wrong way, sometimes. They reject genetic explanations for social problems, such as obesity or drug addiction or violence, because they think it implies that when someone is obese or addicted or violent, it’s their fault. But it’s the opposite. It implies that it’s absolutely not their fault, any more than it’s a short person’s fault that they can’t reach fruit on the high branches of a tree.

For instance, in the case of obesity. Coincidentally there’s another study out, about the genetics of obesity, and it finds that – unsurprisingly – there is a strong genetic component to whether we are fat or lean. Again, that’s confirming something that we largely already knew. But what might be more surprising is that previous research has found that many of the genes that are relevant in obesity are genes that control the brain, not the metabolism.

The neuroscientist Stephan Guyenet’s book The Hungry Brain details how our brains govern our weight; people differ in how attractive they find high-calorie food, and in how able they are to resist the impulse to eat it. And our brains try to keep the level of fat in our bodies stable, but are especially worried about losing fat. So if we end up fatter – because highly palatable modern junk food attracts us even when we’re not hungry – and then try to lose some weight, our brains make us extra hungry to get the food back on.

What’s interesting, though, is how that manifests. Previous experiments had showed that people on severe calorie-restricted diets – starvation diets, essentially – became obsessed with food: they talked about little else, they dreamt and fantasised about food, they “became fascinated by recipes and cookbooks, and some even began collecting cooking utensils”, writes Guyenet.

What was interesting, was that severely obese people who lost large amounts of weight in laboratory settings, but who were still obese and still eating more than enough to sustain life if not weight, exhibited the same symptoms. Their brains ramped up the obsession with food.

OK, you might think. But you still can resist the impulse to eat. It’s still free will.

Think, though, about other impulses in your life. For instance, as Jeff Friedman, a geneticist at Rockefeller, pointed out, you can consciously resist the impulse to breathe – for a while. But eventually that impulse will overwhelm your conscious control and there is nothing you can do about it. “The feeling of hunger is intense and, if not as potent as the drive to breathe, is probably no less powerful than the drive to drink when one is thirsty,” writes Friedman. That is the sort of impulse that obese people have to resist, constantly, to lose weight.

That’s how all these drives must feel. It’s not that laziness manifests itself as a conscious decision to sit on your arse playing Call of Duty rather than going to do your job. It manifests as a powerful resistance to doing something, as though action is almost literally painful. It’s not that drug addiction feels like you’re weighing up the pros and cons of robbing a house to pay for heroin; it’s a drive like starvation, or oxygen deprivation.

Some people are genetically lucky enough to have a greater ability to resist those drives. But that’s winning a lottery of birth, not something morally praiseworthy.

Our society uses the term “meritocracy” quite a lot. It’s a word born of satire, but we use it earnestly. People who pull themselves up by their bootstraps deserve the better life they achieve.

But that’s just not how it can possibly be. There may be unavoidable practical reasons why we give people who work hard greater rewards (on average) than those who don’t, just as we give people who are intelligent greater rewards (on average) than those who aren’t – we need to attract and incentivise hard-working, intelligent people to do the jobs we want doing.

But those people who are able to pull themselves up by their bootstraps will, usually, have attributes – intelligence, self-control – that are as much a lottery as being born rich in the first place.

If you think I’m saying this means that the people who didn’t pull themselves up by their bootstraps are to blame for that failure, then you’ve missed the whole point. I’m saying no one should be blamed or praised for their personalities. This is not the same as saying that everyone who’s successful is clever, and that we don’t need to work to address social injustice.

As the Marxist blogger Chris Dillow points out in the analogous case of IQ, being intelligent is helpful in any social structure, but that structure can still be immensely unjust. “You needed cognitive skills to climb the USSR’s bureaucracy or to pass the civil service exam of medieval China”, he writes, but that doesn’t make them egalitarian paradises.

Just as that is true of intelligence, it’s true of self-control. Being born rich is lucky; being born intelligent is lucky; being born with good self-control is lucky. None of these things makes you a better or more valuable person. Society needs to look out for people who were born with attributes that aren’t suited to modern life, rather than blame them for not fitting in.

The neuroscientist David Eagleman talks about “neurolaw”; rethinking the justice system in the light of the fact that we’re not all equally capable of resisting impulses, and thinking in terms of crime prevention rather than blame: some people might need to be imprisoned for crimes because they’re likely to reoffend, but not for reasons of punishment. Comparably, we need to accept that there are people in society who are born with less ability to work hard, and less ability to control their eating and their substance use, than others.

For a start, this understanding supports the case for taxes on fattening foods or restrictions on advertising for addictive substances – the libertarian case against that is undermined if we are not all equally free to resist them.

And, like the understanding that not everyone is equally intelligent, it implies that society ought to be more willing to provide for people who are less capable in the world of work. Perhaps that means a greater social safety net, more money taken from people who have been lucky enough to be born rich, clever, or hardworking, and given to those who aren’t; Dillow suggests a universal basic income, so that no one is forced to rely on luck to survive in the first place.

But the most important thing that needs to flow from it is a more forgiving approach. You wouldn’t (I assume) believe that people born tall, or good-looking, are morally superior. You should stop thinking that about people born hard-working or slim, too.

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Tom Chivers is a science writer. His second book, How to Read Numbers, is out now.

TomChivers