Genes and the Environment

When I think about genes and the environment, I often think about William Shakespeare because Shakespeare wrote a play called ‘The Tempest’. The plot of this play involves a shipwreck on an island, and on this island lives a little devil whose name is Caliban. The people who were shipwrecked tried to be kind to this little devil, and he turned out to be completely awful: he won’t cooperate with them, he won’t help them, he’s just a nuisance. In great desperation, one of them says to Caliban: ‘On thy foul nature nurture would never stick’: in other words, you were born so awful that nothing we can do to change your environment will make you better.

That’s a very common fallacy when we’re talking about genetics: the nature-nurture controversy. Not many people know that the phrase ‘nature-nurture’ comes from Shakespeare. Frances Galton, who was in some senses the founder of human genetics, was completely convinced, absolutely convinced, as was almost everybody else, that everything was in your nature, the way you were born. He was an outstandingly good scientist: of course, he made mistakes, but all scientists do. He wrote a book called ‘Hereditary Genius’ in which he pointed out that, for example, if your father had been a judge and his father had been a judge, and his father had been a judge, it was quite likely that you would be a judge. But he went further than that: he went up to Newcastle-on-Tine, which is where he used to have rowing races. He found the people who were champion rowers: their fathers tended to be champion rowers, and so were their grandfathers and great-grandfathers. He did this for various reasons, and he found this happened again and again. For him, this proved that everything was in your nature, in your biology; nothing you could do to change the environment would make any difference.

Of course, he was completely wrong. One of the things that are absolutely passed down from one generation to the next, often for many generations, is money. Most people who are millionaires in the modern world are millionaires because their parents were millionaires: that isn’t true for everybody in our technological age, but it has been true for a long time. And there are no genes for money.

So the mere existence of the hereditary pattern is a very weak inside to whether something is genetic or not.

But many people still don’t see that. If you type into Google the words ‘scientists find the gene for’, last time I did it, I got something like 63,000 hits. Given that there are only 23,000 genes, that’s quite impressive. But that’s silly: ‘Scientists find the gene for language, ‘ ‘Scientists find the gene for unhappiness, ‘ ‘Scientists find the gene for musicality, ‘ and ‘Scientists find the genes for height. The most dangerous words in the science of genetics are ‘the gene for…’ because genes are just boring bits of DNA; they work in an environment. Without the environment, they wouldn’t be doing anything. That’s the extraordinary thing about knowing a certain amount about genetics. For the public, that makes the environment seem less important; for geneticists, it makes it seem more important.

I often talk about a classic example, which is cat genetics. I have many examples from cat genetics, and one of them has to do with black cats and white cats. We all know about black cats, and we know about white cats. Charles Darwin actually found something interesting about white cats: all blue-eyed white cats are deaf. Darwin found that. The reason for that is that white cats cannot make the pigment called melanin, and that’s the pigment which we’ve all got. If you have dark hair, you have melanin in it; if you have dark skin, you’ve got melanin in it, but it’s also in your brain, your ears and various other places.

So, a black cat can make melanin in a kind of biochemical production line which starts with simple chemicals and puts them together to make this complicated pigment. If one of the machines in that production line has broken down and if the machinery goes up to that broken point and then goes no further, you’ll have a white cat. That’s simple. But sometimes what happens is that the machine hasn’t broken down, it’s just being slightly damaged, so it doesn’t work very well. And then you get some rather strange patterns in cats. The one I’ll talk about is called the Siamese cat: it’s a cat which has a black nose, ears, and tail, and it’s a male cat that has black testicles as well. The Siamese cat is a genetic mutation; it’s a change in the DNA and the genes. We know exactly what’s gone wrong, we know where it’s gone wrong, we know the exact DNA base in the DNA chain, we know exactly what’s gone wrong there; if we do breeding experiments with other cats, the pattern follows exactly the rules that Mendel found with peas. So it’s genetic: I’m very, very happy to accept that. It’s certainly genetic.

But crucially, it’s also environmental because the reason the cat has got that strange pattern is that the enzyme that does the job of making melanin can do its job well in the cold parts of a cat’s body where there’s less spare energy lying around and bashing the biochemical process. But it does its work much less well in the warm parts of the car’s body, and that’s the main body mass, which is one or two degrees warmer than the nose, the ears, the tail and the testicles, which of course, are both literally and metaphorically the coolest part of any male body. They are black as a result. And if you want to make a dark-coloured Siamese cat, you can do it by breeding for many generations from dark-coloured Siamese cats, or you can take the Siamese kitten and keep it in a cold room, and it’ll be much darker. If you want to make a light-coloured Siamese cat, you can take a Siamese kitten and keep it in a warm room, and it’ll be much lighter. If you want a very expensive black cat, you can take a Siamese kitten, keep it in a refrigerator, and it’ll be a black cat.

So the Siamese characteristic is absolutely genetic but also absolutely environmental, and the two are working together.

That happens again and again and again. We can see it happening in a dramatic way in our own lifetimes. When I was born, which is 75 years ago (depressing but true fact: I was born at the end of the Second World War), after the war, there weren’t any real famines, but there were certain food shortages, and there was what we called rationing. Of course, it was much worse in Russia and Germany, but people here were forced to eat a very simple diet. In retrospect, it was a very healthy diet: very little sugar, very few cakes and so on, almost no butter: this kind of thing. So, people were generally rather thin. Since then, things have changed dramatically. In those days (and indeed in the 19th century and indeed in Russia in the 19th century if you read Tolstoy and so on), it turns out that one of the defining characteristics of the ruling class, the rich, is that they were fat. The peasants were starving; they were thin. And the same was true here, in Britain: if you read Charles Dickens, many of his rich characters in London of the 19th century wore top hats, had cigars and were obese. The poor people were thin.

We’ve now seen an astonishing reversal of that. When I give lectures on this to my UCL students, I look at them – and they’re highly intelligent, a very middle-class group – and I don’t think is a fat person in the class. But if I go to a working-class part of London, obesity is a big problem. In America, it’s a major problem: life expectancy in the United States is dropping fast, and the reason for that is obesity. Why is it? Because food has basically become free. In the 1930s in America, it took a working man more than half of his working week to get enough money to buy food for himself, his wife and two children. Now, it takes him, on average, less than a day to do that as long as he buys cheap, nasty, sugary, fatty food.

So that food is now everywhere, universally available. People eat that food, and they get fat. In fact, we know a lot about the genetics behind that: there is very strong evidence that individuals with particular genes become fat if they eat a lot of food. But those genes only ever manifest their effects in a place where food is cheap. It’s a Siamese cat phenomenon. If there’s no food, it doesn’t matter if you’ve got genes that make you fat because you’re not gonna get enough food. The effect is big. These genes have a very surprising place where they work: they don’t work in the intestine or the liver to change your metabolism – well, most of them don’t. Instead, they work in your brain: nearly all of them are appetite genes. We have all kinds of hormones that change our feelings of hunger; insulin is one. In fact, the first hormone ever found (I have to put an advertisement again for the University College London) was found here, just about two hundred yards away down there, and that was actually a hormone called ghrelin, which was an appetite hormone discovered in 1903.

We all know the feeling of hunger. We’re hungry, so we go to McDonald’s either in Paris or London or Moscow, and we buy some junk food, and we eat it – well, I don’t eat it, and I bet you don’t either, but people eat it, and they say: ‘Oh, that was nice, wasn’t it?’ And I say: ‘God, not for me, thanks’. But you don’t then go again and buy another cheeseburger and another milkshake or the third one because you have other hormones that come in and say: ‘You’ve eaten enough’. These are what we call satiety hormones — ‘stop eating’ hormones: you have hunger hormones and ‘stop eating’ hormones.

Occasionally, very occasionally, people are born who don’t make these hormones, so they’re always hungry. One of them is called leptin, and one birth in 50,000 or 100,000 of children is born with no leptin. As babies, they’re always hungry, and they aren’t pretending they’re hungry; they are screamingly hungry. And so, of course, they scream, and they yell, and they make a fuss, and their parents, of course, are very upset by this, and they give them too much food, and the children become morbidly obese. Fortunately, we now can treat this with injections of leptin, but that’s the nature-nurture thing.

These genes for obesity or not obesity, these hunger genes have been around since humans evolved, but they’ve only become a problem in the last twenty or thirty years when food has become free. So that’s nature and nurture working together.

There’s a second subtlety that people really don’t like to think about, which is that these genes work in your mind. They would definitely work in your mind, and people find it very disquieting that your appetites are changed by your DNA. But I say: well, it’s a hormone. There’s another hormone that shows the nature-nurture thing very well and works in your mind: testosterone, the hormone that makes us men the wonderful creatures that we are. Women have it, too, in much smaller doses: that’s why some elderly women grow moustaches as they grow old. Women have a little bit, but men have a lot more. Testosterone is nasty stuff: it makes men live shorter lives, it makes them much more liable to infectious diseases because testosterone suppresses the immune system, and it makes them much more likely to get involved in being murdered. So testosterone changes your behaviour, and we know very well the way it does it. We know a lot about the biochemistry. Bodybuilders, for example, who use testosterone to get big muscles, tend to die for male reasons: they’re murdered, they’re dying in car crashes, they commit suicide, that kind of thing.

Testosterone works on your mind and one of the things it definitely does is change your propensity for violent behaviour. All over the world, men murder at ten times the rate of women. The murder rate in Britain is fairly low: it’s not as low as in Singapore, but the murder rate in Colombia in South America is a hundred times the murder rate in Singapore. The murder rate in the United States is five times the murder rate in Britain. Now, testosterone is exactly the same in both places, but in Colombia, there are drugs, gangs, weapons, poverty, unemployment, and violence, and this puts part of the population at genetic risk. They’re known as men. They have genes that put them at risk of murder if they’re placed in a murderous environment. If you want to get rid of murder, you do what the people in Singapore and in Britain have done: you get rid of guns. You cannot get a gun in this country; it’s impossible. In Singapore, you try to improve living conditions; you try to reduce unemployment, and all this works. So, you’re solving a genetic problem by changing the environment. And that is probably the take-home, most important message we could take from the modern world of genetics.

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