美国国家公共电台 NPR Moshe Szyf: How Do Our Experiences Rewire Our Brains And Bodies?（在线收听）

GUY RAZ, HOST:

It's the TED Radio Hour from NPR. I'm Guy Raz. And on the show today, hardwired - ideas about what determines our personalities, our traits, our behaviors and even the choices we make. And usually when we talk about the way humans are wired, we're talking about our genetics, our DNA.

MOSHE SZYF: Everything we do is so-called encoded in our DNA. And it comes after millions and millions of years of evolution. And that defines, essentially, a lot of our lives, our future lives.

RAZ: This is Moshe Szyf. He's a professor at McGill University. And you're an epigeneticist, right?

SZYF: Yes.

RAZ: What is it, by the way?

SZYF: The field of epigenetics is interested in how genes are programmed. So if you think about our genes as some sort of a hardware of a computer, epigenetics is the software. It makes it work, right? If you buy a computer that has only hardware without software, it's useless.

RAZ: Basically Moshe tries to understand whether the DNA we inherit is fixed or whether it can change.

SZYF: Right. So this is the big, big discussion of our century. And the idea was very dominant that most of who we are is defined by the kind of genes we inherited from our ancestors. You can look at it as it gives you freedom because it makes no difference what you'll do. If you have a gene that you're going to be smart, you will be smart. And if you're not, don't waste your time studying. And some people believe that there are genes that make us rich, make us anxious or not anxious. So that was the general idea. But as genetic research advanced, there was a good conviction among some people that there must be something else going on in DNA, that DNA by itself is not sufficient to explain behavior.

RAZ: And Moshe has been studying this idea for decades, starting with some groundbreaking experiments with rats. Moshe Szyf tells the story from the TED stage.

(SOUNDBITE OF TED TALK)

SZYF: So it all came to life in a dark bar in Madrid. I encountered my colleague from McGill, Michael Meaney. And we were drinking a few beers. And like scientists do, he told me about his work. And he told me that he is interested in how mother rats lick their pups after they were born. And I was sitting there and saying, this is where my tax dollars are wasted...

(LAUGHTER)

SZYF: ...On this kind of soft science. And he started telling me that when the rats, like humans, lick their pups in very different ways. Some mothers do a lot of that. Some mothers do very little. And most are in between. But what's interesting about it is that when he follows these pups when they become adults - like years in human life - long after their mother died, they are completely different animals. The animals that were licked and groomed heavily are not stressed. They have different sexual behavior. They have a different way of living than those that were not treated as intensively by her mother.

So then I was thinking to myself, is this magic? How does this work? As geneticists would like you to think, perhaps, the mother had the bad mother gene that caused her pups to be stressful. And then it was passed from generation to generation. It's all determined by genetics. Or is it possible that something else is going on here? So in rats, we can ask this question and answer it. So what we did as a cross-fostering expert, you essentially separate the litter, the babies of this rat at birth to two kinds of fostering mothers, not the real mothers, but mothers that will take care of them - high-licking mothers and low-licking mothers. And the remarkable answer was it wasn't important what that gene you got from your mother. It was not the biological mother that defined this property of these rats. It is the mother that took care of the pups.

So how can this work? Is it possible that the mother is somehow reprogramming the gene of her offspring through her behavior? And we spent 10 years, and we found that there is a cascade of biochemical events by which the licking and grooming of the mother - the care of the mother - is translated to biochemical signals that go into the nucleus and into the DNA and program it differently. So now the animal can prepare itself for life.

RAZ: First of all, we don't think of rats being particularly maternal. But I guess they are. I guess they can be.

SZYF: They are. And if you watch rats...

RAZ: No, thank you.

SZYF: (Laughter) You can see that they lick. They groom. And the results are very clear that it's not the biological mother that is important in this case. It is the fostering mother.

RAZ: It's the experience.

SZYF: Yes. So it was very clear around 20 years ago that DNA has two identities - an inherited identity and another identity that is formed during embryogenesis or during the time the fetus develops in the womb of the mother. Of course, the next question was, does it end there? And that is, does DNA have a third identity? Which, I call it experiential identity - the identity of past experiences that somehow also use the same kind of biochemical concepts to give DNA different identities. But then this time, this will be an identity of an experience.

(SOUNDBITE OF TED TALK)

SZYF: But is it true only for rats? The problem is we cannot test this in humans because, ethically, we cannot administer child adversity in a random way. So if a poor child develop a certain property, we don't know whether this is caused by poverty or whether poor people have bad genes. So geneticists will try to tell you that poor people are poor because their genes make them poor. Epigeneticists will tell you poor people are in a bad environment or an impoverished environment that creates that phenotype, that property.

So we can't do experiments. We can administer adversity to humans. But God does experiments with humans. And it's called natural disasters. So one of the natural disasters - the hardest natural disaster in Canadian history happened in my province of Quebec. It's the ice storm of 1998. We lost our entire electrical grid because of an ice storm when the temperatures were in the dead of winter of Quebec - minus 20 to minus 30 - and there were pregnant mothers during that time.

And my colleague, Suzanne King, followed the children of these mothers for 15 years. And what happened was that as the stress increased - and here we had objective measures of stress. How long you were without power? Where did you spend your time? Was it in your mother-in-law's apartment or in some posh country home? So all these added up to a social stress scale. And you can ask the question, how did the children look like? And it appears that as stress increases, the children develop more autism. They develop more metabolic diseases. And they develop more autoimmune diseases.

RAZ: So the mothers passed on the stress factor to the babies?

SZYF: Yes so we looked at their DNA, you know, when the kids were 15 years old - DNA in the blood and immune system. And we saw many, many differences in the way the epigenetics was programmed. So this, in my opinion, was, you know, one of the first evidence that in humans, too, an experience can result in long-term changes to the way genes are programmed.

RAZ: So this would suggest that we are prone to constant change based on our environment. Or am I wrong?

SZYF: No, no, you're absolutely right. So on one hand, we have an old genome - right? - that's millions of years old that's fixed. On the other hand, we have a changing world that is talking to our DNA. And this balance, probably, was selected by many, many millions of years of evolution to provide with us with this amazing, what we call, plasticity on one hand and fixed characters on the other hand, right? So we need both. We need the immutable and mutable operating together. And that's the amazing paradox and challenge of life.

(SOUNDBITE OF TED TALK)

SZYF: DNA is not just a sequence of letters. It's not just a script. DNA is a dynamic movie. Our experiences are being written into that movie, which is interactive. You're like watching a movie of your life with the DNA with your remote control. You can remove an actor and add an actor. And this has a tremendous optimistic message for ability to now encounter some of the deadly diseases like cancer, mental health, with a new approach. We can epigenetically intervene, reverse the movie by removing an actor and setting up a new narrative.

RAZ: You know, Moshe, we were talking with Robert Sapolsky earlier. And he kind of questions how much free will we actually have. But - I mean, but if you say DNA is like a dynamic movie, I mean, it seems like you could also make the argument that we actually do have some agency over who we are.

SZYF: Absolutely. And I think the word agency is extremely important. And the question is, who has agency, right? Is it you as an individual? Is it you as a family? Is it you as a community? Is it you as a country? Is it you as a world? And I think all of the above. So agency is now split. It's not just you. The agency is the interactions between all these elements. If this is true, and I believe it is, there is a lot of hope. If you look at it - look at humans, what they have done in the last hundred years, we've doubled lifespan, right?

RAZ: Yeah.

SZYF: I think it's the wellbeing. I think it has to do with much lower levels of adversity in at least in some parts of the world that humans were used to for thousands of years, right? We know our next meal is there. And that knowledge, you know, removes a tremendous amount of stress from our lives. Of course, you can always argue that all of this was pre-wired. Like, the script was pre-written, including those changes. But I think that there is - between the hardwiring and the ultimate result, there is a space where freedom of will is operating. And it's operating on those epigenetic processes. If we understand these processes, tap into these processes, we can be ruler over our genes by providing the right environments. And that's where we as societies have a responsibility.

RAZ: Moshe Szyf is an epigeneticist at McGill University. You can find his full talk at ted.com.