Our bodies are imperfect, -for good reasons

 

Randolph Nesse

 

 

Randolph Nesse is a physician and psychiatrist who used to be frustrated with psychiatry's lack of theoretical foundation. In 1985 at a meeting of a group that later developed into the 'Human Behavior and Evolution Society', he met and discovered shared interests with George Williams. Their cooperation resulted in several publica­tions, among them Why We Get Sick, The New Science of Darwinian Medicine (1995). The following interview took place in Tucson, June 1997.

 

There is a story in your book about mice that hate the smell of cats. What is it about?

 

I think we use that story to illustrate the benefits of fever. The mice did not like the smell of cats, and therefore they got a drug so they were not bothered so much by that smell. They felt better in the short run, but then they died, because a cat obviously would eat them. We compare that to someone whose normal fever was blocked by doctors who block a defence without thinking about it.

 

So although the mice were suffering from the smell of cats, this suffering is actually useful to them.

 

Exactly. One of the main ideas I have pursued is that natural selection has shaped the capacities for emotions. Nega­tive emotions are just as useful as the positive ones. So anxiety and boredom and jealousy and anger and low mood are all useful in their place. The temptation for doctors or psychologists is to assume that if someone feels bad, that there is something wrong with them. That either their brain is not working right, or their cognitions are not working right, or something like that. But in fact, if you take an evolutionary view, it is very likely that a whole lot of suffer­ing is just normal mechanisms working, usually in situ­ations that are not very favourable to us. Obvious­ly, if you are experiencing pain, it is not a good situa­tion, because your tissue is being damaged. You have got to get out of that situati­on. But the pain is not the problem, the problem is whatever is damaging your tissue. Likewise, if you are feeling anxious or low, probably bad things are going on in your life. You should try to stop them. And if you stop them just by block­ing that emotion with a drug, that might not be the best thing. But I would like to stress that there shouldn't be any clinical recommendation that comes out of Darwinian medicine directly. Darwinian medicine should lead us to research-projects we never thought of before.

 

You write that medical professionals have often been asking the kind of questions you are asking. What kind of questions are these, and why are your answers different from the ones they gave?

 

If George Williams and I have contributed anything to this field, it is a very small change in perspective that has fairly large implications. Ever since Darwin people have talked about the evolution of disease. This is a mistake. Diseases don't evolve, but the body's vulnera­bili­ties that lead to diseases, they are a product of natural selection. What we are encouraging people to do is to try to understand why the body is not better. Why can't natural selection make the body better? People used to say "Well, natural selection just isn't that good". That might not be the right answer. Some people imagine that George and I are saying that the body is perfect, because natural selection is such a strong force, but we are saying the exact opposite: The body is imperfect, -for good reasons. And that is not an idea that is very common among medical re­searchers yet.

 

So why are there so many complaints about how our bodies functi­on?

 

We list several categories of explanations. One of them is that what seems to be a disease, is often a defence. So fever, cough, nausea, pain, vomi­ting, diarrhoea, anxiety, low mood -those are not pro­blems, those are responses to problems. Fever decreases the ability of bacte­ria to reproduce. Even cold-blooded animals go to warmer places when they get a bacterial infection, in order to kill off those bacteria.

When people go to the doctor they usually complain about these defences. They complain of fever, nausea or pain, fatigu­e or vomiting, and about half of the medical practice is bloc­king those defences. The next questi­on is: Well, if all these defences are so great for us, how can doctors get away with blocking them all the time? I think there are two answers. One is what George and I call the 'smoke detec­tor principle'. That is, the defence is cheap, vomiting for instance only costs you a couple of hundred calo­ries. Vomiting is really essential if you are about to die, or if you have any chance of dying from a toxin that is circulating in your system. So if there is any chance of a toxin in your stomach, you should vomit. Likewise for fever. If there is much of any chance that there is a bacteria in your system that might be damaging it, it is in your best interest to increase your body-tempera­ture.

 

So often your body-temperature is raised while you could get healthy wit­hout raising it?

 

That's right. We take aspirin and we usually get better anyway, just as fast, without having to go through a fever. The other reason why doctors usually get away with blocking defences is that the body has redundant mechanisms. There are other mechanisms that do the same thing, it is not just high fever that kills bacteria. So that is another reason why we can get away with blocking fever.

This has the biggest implicati­ons I think for new drugs that are being invented for regulating human emotions. Already we are getting pretty good at blocking low mood. And I ask myself the question: What is going to happen in the next ten to twenty years if we develop all kinds of new drugs to block low mood and anxiety safely without addiction? How should we use those drugs? We have been thinking about those emotions as abnormal, and I am trying to help people to see that these emotions are useful in certain circum­stances. On the other hand, given what I just said about the smoke detector principle and the redundancy principle, it might well be that a high proportion of emotional suffering that people expe­rience, is completely unne­cessary.

 

You write that survival is of no consequence in and of itself. Is the body not designed to survive?

 

You get a very different view on medicine and disease once you start taking the evolutionary perspective. Survival is just one means by which genes make organisms that get more genes into the next generation.

So for instance you could ask the question: Why is it that males die sooner than females in many different species? The proximate answer, -that is the biochemical answer-, is that they have more testosterone. The evol­utio­nary answer has to do with: Why is there more testosterone? The answer appears to be that for males, reproductive success varies a lot more than for fema­les, and increased investment in competiti­on early in life can have a big reproductive pay-off. There­fore men who do more competitive things, and devote fewer resour­ces to for instance defending against infection, have a reproduc­tive advantage over men who live longer.

 

Another quote: Some current medical research seems a bit like trying to under­stand a clock's malfunctioning by analysing all its gears, without daring to ask about their functions.

 

The distinction between proximate explanations and evolutio­nary explanations is very simple, very profound and very misun­der­stood. A proximate explanation is how something works, it is what the mechanisms are like, how the gears are connected, how the chemicals work, how development works from DNA to shaping the whole organism. An evolutionary explanation explains why the DNA has the exact sequence of amino-acids that it does, in turn, why the organism is the way it is. And that has to be framed in terms of how a certain trait gives a selective advantage. This all sounds very technical; it is much easier to do it with examples. The one I use a lot in lectures is: Why do polar bears have white furs? The proxima­te explanation is that the polar bears' body doesn't make pigment for the fur. The evolutionary explana­tion is that white polar bears catch more seals than brown ones.

 

A major cause of disease is infection. The accepted view is that hosts and parasites will slowly evolve to some coop­era­tive state. What is your comment?

 

We are all taught this at school, and even many micro-biologists until the last couple of years still imagined it to be like that. On the surface it doesn't make sense to say that the parasite or pathogen should kill its host, because how is it going to survi­ve without the host? It would be better if they could live with their hosts and gradually evolve into a mutual harmony where they don't hurt each other too much, and both go along.

That turned out to be a very naive view. Paul Ewald and a number of other people showed that virulence, -that is how nasty a pathogen is-, is a trait that is shaped by natural selec­tion. He showed that if an infection is transmitted by something that doesn't require the person to be up and around, like a mosquito, a nurse's hands, or a syringe, then whichever pathogen makes the most copies of itself the fastest, is going to get passed on. So selection is going to make it worse, more virulent; because while making many copies of itself, the parasite will exhaust the host. But if the person has to be up and around to spread the infec­tion, like with a cold or like with cholera once good sewage-treatment comes in, then those that kill off someone right away will be selected against, while those that are a little bit more mild will be selected for. If proper sewers come in, the more nasty form of cholera is quickly displa­ced by a milder form.

 

Why was the cholera nasty in the first place?

 

Because the greatest advantage to the cholera organism was to make as many copies of itself as possible. Even if the person that was lying in bed was unable to get out of bed, all of the diarrhoea and copies of the cholera-organism flowed into the common public water-sup­plies. As soon as you have proper sanita­tion, that road of transmission is gone, and you have to get that person up and out of bed, to transmit it.

 

So the pathogen now needs its host to be healthy...

 

And of course, we all talk this way, "the pathogen needs", and we all know when we talk that way, it is not that the patho­gen needs anything, there is not any planning involved, it is just that those pathogens that do cause a bit milder illness transmit themsel­ves better.

 

You wrote about an arms-race going on between pathogen and host.

         

Once you start realizing the layer and layer and layer of complexity that goes on between bacteria or viruses and the host that is trying to control them, it is just astoun­ding. Each one of these nasty things has to get into our cells sometime. And so they usually imitate something useful to us, like a hormone. By imitating something that is naturally in our body, it gets hard for our body to attack the parasite, because then we are likely to attack ourselves.

Once the parasite gets into our cells, the body has certain ways of identifying that something is wrong, and the cell lit­erally holds out a little flag to the rest of the immune-system saying: "Listen, I have been infected, kill me off". And then the rest of the immune-system comes in and kills off that cell, with everyt­hing that is in it. But of course the bacteria and viruses want to stop that from happening. So certain bacte­ria and viruses have the capaci­ty to block that cell from signalling to the rest of the immune-system. But then the body has other ways to getting around that, to otherwise detect that the cell is infected. So layer and layer of deception, detection of decep­tion, and again decep­ti­on in an arms-race that escala­tes. The reason that George and I have used the term arms-race, is because just like in a race for intercontinental missiles or nuclear bombs, this one can absorb a whole lot of an organism's energy, to the point where it gets detrimental to the whole. For example, if you look at the amount of disease by auto-immune reactions, you realise those are mostly caused by arms-races with pathogens. Our system has to be set to be able to make anti-bodies to attack parasites, and sometimes it goes off when it shouldn't, and it makes anti-bodies when it shouldn't.

 

You also give examples of how parasites can manipulate the behavior of hosts.

 

The simplest ones actually are not in humans. There is a fluke that is so tiny that it can enter the brains of ants. The ants are crawling around on the sheep-meadow. The fluke enters the brain in such a way, that somehow it induces that ant to crawl up to the top of grass, and grab on so it cannot let go. And of course, those are the ants most quickly eaten by the sheep, and they are the next host in the life-cycle. There is something very similar in snails, they are infected by a diffe­rent organism, and they crawl up on the beach and are the first to be eaten by seagulls.

Rabies is even more dramatic. Once it gets into the system of the host it gets into the nerves, and it arranges in a sophis­ticated mechanism for its own transport to the brain. Then it becomes concentrated in several areas in the brain, in the areas that regulate aggression, swallowing, and the salivary glands. So you end up with a host orga­nism that has lots of saliva full of rabies-virus, that can't swal­low, so the saliva builds up in the mouth, and that becomes very aggres­sive and bites. All of which is to the advan­tage of the rabies-virus. Nobody planned it this way, it just works.

 

Sneezing, is this a host being manipulated?

 

Who knows what sneezing is? Is sneezing for our benefit, for the viruses benefit, or for both? It might be that the virus is manipulating us, to spread itself in a cloud of droplets. It might be that we are sneezing in order to clear up things from our nasal passages, and to prevent the infection from getting into us. Or it might be for both our benefits, and at the cost of everybody else that is around us.

 

Many infectious diseases can now be treated with anti-biotics. What is an anti-biotic?

 

An anti-biotic is some chemical that kills bacteria more readily than it kills us. Where they come from is more interes­ting. It is really neat to learn that they just don't come out of nowhere. These are chemicals that are made by bacteria and fungi, usually ones that live in the soil. Why do they make nice things for us? Is that some kind of divine force providing beneficent drugs for us in the natural environment? No, it is because those bacteria have been fighting each other for not just millions of years, but hundreds of millions of years, and almost any compound they can make that inhibits the growth of their competitors has been tried. In contact with some competitor they start making more of these compounds, and sure enough, some of the very best antibio­tics that we have, are products that have been in the eco-system for years, made by fungi and made by bacteria to defend themselves against other living organisms. And we are just extracting those chemicals, purifying them, and using them in humans. We are borrowing these things that have been created by natural selection in bacteria over millions of years for our own use.

 

You give quite some attention to toxins, and write: There is no such thing as a diet without toxins.

 

At least there is no such thing as a perfect diet. I always thought before I came into this field that there was some diet that we were meant to eat that was perfectly healthy. But like every-thing else in the body, it is all a trade-off. You can eat vegetables constantly, but most of those vegetables have things in them that are designed to keep them from being eaten.

 

But there are no toxins in meat usually. Why are there toxins in vegetables, and not in meat?

 

Because vegetables cannot run away, so they use other means to defend themselves.

 

You give some advice about what to eat when you are starving in an unknown wilderness.

 

This is not a matter where I would really want to follow the advice directly from Darwinian medicine, some expert advice from the locals would be better. But just theoretically, if some animal is adverti­sing itself to you because it is brightly coloured or readily available, it probably means that it is not very good to eat, because otherwise something would have eaten it. Why did natural selection favour it to have a bright colour? Because it warns other things to stay away. Deception may be going on here too: Things that pretend to be poisonous, while they are not.

If on the other hand something is hard to get at, like it is inside a shell or the like, that is an indicator that it is good to eat, if you can get to it. But what you really should do in the unknown wilderness is ask someone else to taste first.

 

How is it that unripe fruits, like some green apples, can give you a pain in the stomach?

 

The proximate explanation is: because they have a bunch of bad chemicals in them. The evolutionary explanation is that apples that are eaten prematurely don't spread their seeds, while apples that have a way of gradually developing while they are safe from being eaten, are able to mature to the right moment, then sudden­ly turn the right colours, express all the sugars, and take away the toxin. Fruits are obviously designed to be eaten, because those that are eaten spread the seeds of the plant. That is your first choice in the jungle: Find something that is a fruit that is designed to be eaten.

 

You write about a mismatch between our design and the present environment. Out of this mismatch arise perhaps the most preven­ta­ble modern diseases. Can you give some examples?

 

If you go and make rounds in modern hospitals, nearly half of the people who are there, are there because of diseases that are caused by the modern environment, that they would not have gotten if they lived in a more natural ancestral environ­ment. What are these diseases? Well, first of all, the diseases caused by bad diets. Then there is the huge burden caused by substance abuse. The worst of which is cigaret­tes, then alcohol, with cocaine and all the other drugs causing just a minute amount of problems compared with alcohol and tobacco. Breast-cancer may well have to do with a change in reproductive patterns. It is much more common now then it used to be.

Once you have taken those diseases away, you have dealt with about half of the people in the hospitals. Does this mean that if we all lived in the African savanna without any medicine that we would be healthier? No, we would be much less healthy, we are not arguing that things were better off back then, we are only arguing that nowadays most diseases are the product of the mismatch between our environments and our bodies, which were designed for a very different situation.

 

You also wrote that frustration may result from consistently overes­timating ourselves. Why would we do this; overestimate oursel­ves?

 

If you ask people in large cooperations, do you think you are paid what you are worth? Most will say: I am worth more than I am being paid. On the average people over-as­sess their own value to the organisation. So let's ask ourselves for a second: Wouldn't it be good for people to be objective about their usefulness for the group? Probably not. Probably people who are completely objective about themselves don't get the advantages that come to some other people who think that they are a little better than they are. Because if you can pull off convincing other people that you are more valuable than you really are, then you get all the advantages that comes from that status. In fact, if you look at social life, there are all kinds of social dis­plays that are essentially deception, where people are trying to act like they're richer then they are, or sexier than they are, or smarter than they are, or something, in order to convince people. If you believe it yourself, that works pretty well.

 

Some people are worried by the idea that because disea­ses are treated, the problem is just moved to the next genera­tion.

 

Ah, the eugenics-question. Often when I lecture somebody says: "Well, isn't medicine making the species less healthy?" That has been a question that has been raised, since the middle-ages at least. The people who raised it the most seriously were the Nazi's, who thought that doctors were making the stock worse by preserving the lives of some sick people. The whole eugenics move­ment took very seriously the possibility that you could improve, quote, the genetic stock.

First of all, according to my values, it is wrong to do that kind of thing, so-called for the benefit of the species instead of the individual. More than that, there is very poor scienti­fic justification. From what we now know about gene-frequencies and their relationships to disease, the amount of impact you would have from even very strict reproductive controls on people with diabetes, heart-diseases, schizophrenia and other kinds of diseases, would be very small and only in many generations. Plus a lot of the so-called genetic diseases they were treating probably were not genetic diseases anyway. So one question is: Are you really sure about what you are dealing with? Who knows what inventions will be availa­ble for the next genera­tion? There does not seem to be any likely benefit that would be worth interfering with peoples rights. So George and I have tried as strongly as we can, to say that our purpose is not to use evol­ution for the benefit of the species. Our purpose is to use natural selection theory in the tradition of mainstream medicine, for the benefit of the indivi­dual pa­tient. 

 

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