Remember meForgot password?
    Log in with Twitter

article imageEvolutionary medicine: An interview with Randolph Nesse

By Bart B. Van Bockstaele     Feb 15, 2009 in Health
Professor Richard Dawkins, one of our leading evolutionary biologists, talked with Dr. Randolph Nesse about evolutionary medicine for his program about the genius of Charles Darwin. This important interview can now be seen in its entirety on YouTube.
Please note that this interview was never meant to be aired in its entirety. This is not a television programme. It is raw footage from which parts would be (and have been) used for his three-part documentary about Charles Darwin that I discussed earlier.
The theory of evolution is one of the fundamental truths discovered by science. It is just as important, and maybe even more so, for biology as classical mechanics is for physics. “Nothing in biology makes sense except in the light of evolution,” said Dobzhansky, but in spite of this, many medical faculties do not teach much of it to their students. That is a pity, says Randolph Nesse, so many things would have made a lot more sense while I was studying, if someone had explained how natural selection works.
Randalph Nesse, one of the founders of modern evolutionary medicine, says that our bodies are obviously not designed but evolved.
“What really gives the proof is when you look at how badly designed they are. No sensible person would have ever left the body the way it is.”
Professor Dawkins asks for a good example, and Nesse gives several. Probably the most compelling for many people is the eye. Often cited as an example of a perfect instrument that just had to be designed by some creator, it is, in fact, just the opposite.
Our eyes are shamefully badly designed. In the back of the eyeball, there is a place where the blood vessels and the nerves enter the eye through a hole, the “blind spot”, completely blocking incoming light from being captured. The are then spread out over the retina, blocking part of the incoming light from being captured. This is such a botched job. To add insult to injury, there are animals with splendid eyes that do not have that problem, such as octopi.
Nesse also mentions that it is very important to understand that evolution by natural selection is not “for the good of the species,” not even for our own good, but simply for the benefit of the genes. He goes on saying that calling the human body a machine is incorrect.
Machines have blueprints and they are constructed according to a master plan. Once finished, all machines created will be largely identical. If something does not quite work, the engineer goes back to the drawing board and starts over. Not so for humans. They have a genome, an evolved genome, and they are stuck with it.
One of the characteristics of evolution is that it cannot “undo” things; it can only build further on what is already there. There again, the eye is a good example. We have a nystagmus, involuntary little movements of the eye. They compensate, at least partially, for the existence of our blind spot. Therefore, while nystagmus may seem like a problem, it is also a solution found by evolution to compensate for the problem it created in the first place.
Another characteristic of evolution is the existence of trade-offs. One example is the so-called Colle’s fracture, a fracture just above the wrist that is very frequent. Evolution could have easily avoided that by making our forearm bones thicker, except it did not. Why? Because it would make rotation of the wrist a difficult thing. In robotics, this problem does not really exist, because the forearm is made out of one metal rod. However, our forearms have two bones, radius and ulna, and because we cannot de-evolve, we are stuck with them and this restricts further evolution.
Some people imagine that there is a “normal” genome. Not so, there are only genes. The genes that make bodies that reproduce more successfully than others will eventually become more frequent in the future. Our genome is nothing more than a collection of genes that work. There is no such thing as a "normal genome."
Nesse goes on to explain the so-called “smoke detector principle” which is somewhat similar to the more widely known “precautionary principle”. The smoke detector principle is the name for a system where the cost of safe behaviour is balanced against the cost of unsafe behaviour.
Smoke detectors can be very annoying because they tend to go off when there is no danger. However, they are set this way because we want them to go off every single time there is a fire. We do not want them to go off only half of the times there is a fire. Therefore, we put up with the false alarm, because the cost of a false alarm is far less than the cost of the lack of an alarm when danger is real.
As an example, he asks “wouldn’t it be great if we didn’t have anxiety?” Maybe not.
For example, imagine a watering hole in the African savannah. When you go to drink, you might encounter a lion that wants to eat you. If you always run away at the first sign of possible trouble, you will not will not get to drink very often and that is not a good thing. If you wait to run away until the lion is right on top of you, you will not survive, for he will have you for lunch. Therefore, evolution chooses a middle way, which keeps us quite safe and still enables us to drink and stay alive.
So, anxiety is not a disorder, it is a protection mechanism that simply happens to be more sensitive in certain people than in others.
Dr. Nesse gives a few other examples of such mechanisms. Pain is one of them. People who are unable to experience pain are usually dead before adulthood. Pain, while unpleasant, does keep us safe. Other examples are fever, sneezing, coughing, vomiting, and diarrhoea. While thoroughly unpleasant, they do protect us.
If that is so, why can doctors safely block these phenomena? Because they are nearly always false alarms. Nesse points out that one of the next steps in evolutionary medicine will be to find out when it is safe to do so, and when not. He also mentions that people want a simple answer to this, and that it is very important not to give them one (because there isn’t one in the first place).
And then he gets to the heart of it: evolutionary medicine doesn’t tell us what to do, it tells us what questions to ask, and what studies need to be done.
He mentions that there is a lot we don’t know yet, and that many studies still need to be done, but he also says that much of it is already practiced by modern medicine, such as when a doctor will refuse to give a patient codeine if she doesn't cough (because it hurts) when she has pneumonia.
He would like that textbooks on disease would add an evolutionary paragraph to every disease description so that they would not only explain how things go wrong and how to correct them, but also what makes this particular function vulnerable to breaking in the first place.
Richard Dawkins then asks about cancer and Nesse starts of by saying that the chances to get it increase with age. He then talks about organ regeneration. We can regrow skin, and even liver, but other organs cannot be regrown, such as the heart or the brain. Why? Because animals whose brains or hearts are damaged will simply not survive in nature. Therefore, a mechanism to regrow them never had a chance to evolve.
In cancer, cell reproduction spins out of control. The body does have some defences against that. One of them is the existence of telomeres, bits of DNA that are shortened at each cell division. Once they are gone, cell division stops and the cell eventually dies. A marvellous safety device. Unfortunately, there is a cost to it. When we get older, and the cell has had its number of cell divisions, it will stop reproducing and eventually die, and so will we, when enough cells have died off.
Nesse mentions a recent study in which it has indeed been shown that people with longer telomeres do live longer lives. The next part of the story will be to show that they are also at a greater risk of developing cancer. If confirmed, it will be a dramatic example of the evolutionary tradeoffs seen in our bodies.
Richard Dawkins then asks the 1-gazillion dollar question: if natural evolution is so good, then how come we do get old and die anyway?
Randolph Nesse goes on to explain a beautiful fallacy. He used to ask the question: why doesn’t natural selection make us live longer?
He was convinced it should, albeit only because we know that there is a lot of genetic variation in how long we live. Since we know that there are different genes that make us live longer, why did natural selection not favour the genes that make us live longer? Most of us die when we are around 80 years old (if nothing goes wrong). By the age of 100, just about all of us are dead.
He came up with a fabulous explanation, or so he thought. He thought it was very important for the species to kill off older individuals to create more room for the species to evolve and adapt to a changing environment.
Dawkins jumps on that to explain that this is the wrong way of looking at things. Natural selection is not about longer lifespans at all; it is about maximizing chances for reproduction, something even Darwin already understood. From an evolutionary standpoint, living long is simply not important.
Nesse goes on to say that people think that living healthy lives is what natural selection has shaped, but of course, it is not. It shapes maximizing reproduction, and if that shapes you to live a shorter lifespan, that is just too bad.
The likelihood of dying increases when we get older and he then says that if this was not the case, if the likelihood of dying would stay the same as it is at age 20, about one third of us would live to be a thousand years old.
He cites an example by the great biologist George Williams. Take a gene that makes bones heal more quickly by changing the calcium metabolism just a little bit. That gene would be selected because, during early life, bones are broken quite often, and healing them rapidly, has a clear advantage. However, suppose that this same gene also has the side effect of encouraging calcium deposits in coronary arteries, and that it would kill everybody at age 120. Too bad, since that gene gives an advantage in early life, it will increase, even though that same gene has the side effect of killing everyone later on.
Dawkins takes this and goes on to explain that a gene that makes you die when you are young (i.e. before reproduction), will never make it into the next generation, and will therefore not stand a chance. On the other hand, if that gene has its bad effect later on, it has more chances of making it into the next generation, and if doesn’t have its bad effect until you’re a hundred, it will get through all the time. Therefore, we are a kind of walking dustbins of genes that will kill us later in life.
After all, none of our ancestors died young (i.e. before reproducing). Think of it: How many of your grandparents died before they could reproduce?
Richard Dawkins asks a simple question “What is Darwinian medicine and what can it tell us?” Nesse gives an equally simple answer “It’s using everything we know about evolutionary biology to prevent and cure disease.” He elaborates by saying that it means that there are many things we need to do differently, and that we are already doing that in some respects.
For example, we do evolutionary genetics quite well and we are doing it better and better. We are using evolutionary genetics to understand bacterial evolution and antibiotic resistance, which has already been done well. The larger picture is a sense of what a body is as a body and not as a machine.
It all boils down to ask a question that wasn’t asked as seriously before: why isn’t the body better? To simplify, he lists six different possibilities:
1.a other things evolve faster than we can (such as bacteria), so we cannot catch up.
1.b the environment is different now, and we have not evolved fast enough to catch up.
2.a natural selection cannot do everything; there are many constraints. Mutation lets errors creep in and we are stuck with them.
2.b tradeoffs. Even though it may sometimes be possible to create a perfect machine for a certain function, this perfection may create other problems that are not so good.
3.a we misunderstand the body. It was not shaped for health; it was shaped for reproduction.
3.b fever, pain, nausea, vomiting and the rest are not diseases, they are defences.
Nesse goes on telling us that evolutionary medicine is not really about practising medicine differently, at least not immediately, but about having a different view on things and asking different questions.
He tells us that we may soon have the capacity to simply knock out genes that are involved in aging. Would it be wise to simply go ahead and knock them out? Although the obvious answer may seem to be a resounding, unqualified yes, evolutionary medicine teaches us to be very careful about this. If natural selection has preserved "genes for aging," there is probably a good reason for this, and getting rid of them may not be such a bright idea.
Richard Dawkins asks a question that bothers quite a few of us: why do males die younger than females?
Nesse replies that this happens not only in Western countries but that data of the World Health Organization show that males universally die about 7 years younger than females, and he goes on to tell us about a remarkable statistic. For every 100 women who die at age 20, how many men die at age 20? It turns out to be a whopping 300.
I have to add a personal note here. This is the type of numbers that people will use to “demonstrate” that one can prove anything with statistics. This is false. Please note that he is explicitly talking about how many men die for every 100 women that die. He is not talking about the total number of women, and he is also not talking about the total number of men.
What is the explanation? Tradeoffs. Males must invest more in finding mates to reproduce than females. Because of that, natural selection has favoured genes that increase that ability and as a consequence, males have less invested in tissue repair. As a result, they die younger. Incidentally, this is also true for our close cousins, the chimpanzees.
Both men then talk about a crucial issue that is often misunderstood by non-scientists. Evolution explains how we came into existence, and how we became what we are. It does not, by any stretch of the imagination, dictate that this is how we must live our lives (even Darwin himself already warned against this fallacy). Not socially or politically, but also not biologically. Going around reproducing like mad is not a good idea for humans.
Eating the stuff natural selection has evolved us to crave, such as sugar and fat, will shorten our lives, and not make them longer. We evolved these cravings, because this stuff was hard to come by on the African savannah where we evolved, but we have it in abundance now. Therefore, the challenge is not to eat as much of it as we can, but rather to stay away from it, and to eat more of the things natural selection has evolved us not to like as much.
More about Evolutionary medicine darwin, Randolph nesse, Richard Dawkins
Latest News
Top News