Speech 2009 by Dr. Stephen Stearns

This speech was given during the Dies Natalis ceremony in 2009: 'Biodiversity as natural capital'.

Stephen Stearns

“Professor Kropff gave me 25 minutes to cover Darwin and biodiversity as natural capital and I’m going to try to take a broad view but by necessity it’s going to go trough fairly quickly. Now, right at the beginning of Darwin’s thinking, biodiversity is the stimulus of his thought. He looked around, as we all do, and we see that the world is really wildly diverse and there are lots of different kinds of organisms out there. Many of them appear to be separated one from another, by appearance, behaviour, ecology, genetics. He asked himself, it was the big question, it was the species problem: Why is the world structured like this, how did it come about? And I want this image to stick in your mind; this is not the Darwin who is 71 years old, it is not the 32-year-old Darwin who is back from the voyage on the Beagle, this is the 7-year-old Darwin. He is holding some plants in his hand and he is looking at the world, and the world is amazing. And at the end of the ‘Origin of Species’, he writes in that paragraph which is so often quoted about there being “grandeur in this view of life”; he writes about “endless forms most wonderful and beautiful..”. And when you think about by biodiversity, I want you to begin with the young child, looking at the world and being astonished by its beauty.

Now, biodiversity is essential for natural selection, so it’s a key element of his thought. Without any genetic diversity there can’t be a response to selection. And therefore diversity is actually the fuel that runs evolution and if the fuel runs out, the engine is going to stop. Now, for intra-specific diversity – genetic diversity within species – it will be regenerated by mutation, so it’s not an irreplaceable fuel.

But for species diversity; it takes much, much longer to replace the species. Just to give you some idea; after the Cretaceous extinction, after the meteorite impact in the Yucatan, it took about 25 million years for the world to become as diverse as it had been before the meteorite impact.

We are currently in the middle of an anthropogenic extinction crisis, it is not clear yet exactly how it will be. But from the direction it is going it looks like we may have an impact on the planet about as big as the meteorite did. And if you think about your descendants and you ask: When will we again see a planet which is as diverse as the one that existed say, 10.000 years ago? The answer is: it might take 25 million years. And I can assure you that whatever sentient being is then perceiving that diversity, it will no longer be called homo sapiens.

Now, to give you some feeling for just exactly how powerful natural selection is; all domestic dogs are derived from the wolf. And it took about 4000 years to do this. So that’s pretty impressive, that goes rapidly. But of course, this is an agricultural university and here are some Peruvian potatoes. There are actually about 300 varieties of Peruvian potatoes, I’m only showing you two of them. Based on that, of course, plant breeders can do this. So as professor Kropff just told you, biodiversity is actually at the basis of almost everything that an agricultural university tries to do.

It is also essential for disease resistance. It is well-known in agriculture that monocultures are at risk, that polycultures are resistant and that natural populations of crop relatives are really a key resource for getting resistance genes that you can breed into crop plants.I grew up at a sugar cane plantation in Hawaii. The Hawaiian Sugar Technology Association was always sending its crop geneticists down to New Guinea to get wild grasses to bring back to Hawaii to breed into the sugar cane, so that they could stay one step ahead of the crop diseases. So it’s been clear to me, from the time I was a seven-year-old boy, that this was an important process. And of course, if you get plant diseases they look fairly horrible and some of them are really extremely destructive. These here are rusts that are infecting cereals. The genes for resistance come from natural biodiversity.

A similar situation exists in medicine. And I think that in medicine biodiversity is actually a double-edged sword. Because on the one hand we have the destructive biodiversity of antibiotic-resistance evolution in bacteria and on the other hand we have the constructive biodiversity of the human race. I’m going to show you both of them. So, on the one hand we have antibiotics and then we have human diversity for resistance and for susceptibility.

This is the environment in which antibiotic resistance evolves. There are about a ton of bacteria in an acre of agricultural soil, that’s a little less than half a hectare. That’s about 1017 bacteria. And they contain enormous genetic diversity, they have been evolving with each other and with the fungi in the soil for millions of years, and they are biochemical powerhouses. They have incredible synthetic ability.

A few facts: if you go out into the soil of the Netherlands or the US and you just take a sample of the soil; you will find that most of the spore forming bacteria in the soil contain genes for some kind of antibiotic resistance. In fact, no existing class of drugs is effective against the natural diversity of antibiotic-resistance in soil bacteria. Some biologists in Australia went around the outback and they took samples of enteric bacteria, gut bacteria, out of mammals that had not had any contact with humans. They discovered that they were multiply resistant and they had no history of contact with antibiotics.

But once you get into agriculture it gets more interesting. Vancomycin is one of the last lines of resistance against multiply-resistant Staphylococcus aureus, which is MCRA, which is a real threat to our ability to do surgery in our hospitals. Antibiotics are used by farmers because by using antibiotics they can decrease the amount of energy that their pigs and their chickens and their cattle are investing in disease resistance and they divert this energy into growth. So they can grow more pounds of food, more rapidly.

Some Danish pig farmers decided to use Vancomycin. When the Danish government discovered this and decided it was a bad idea, they banned Vancomycin. And the rate at which Vancomycin-resistant bacteria were detected in Copenhagen dropped from 9% tot 3%. That estimates how much antibiotic-resistant bacteria were moving from pigs into humans. It’s a comment on a lot of things; it’s a comment on evolution, it’s a comment on how clean pig Danish slaughter houses are, lots of stuff like that. But it’s kind of frightening to think that that’s going on.

Hospital-acquired resistance to antibiotics is probably the primary concern. The Centre for Disease Control in the US, estimates 90,000 cases a year in which a human being went into the hospital without a bacterial infection, acquired it in the hospital and died from it. And that is more than the sum of people who die from AIDS, from flu and from breast cancer per year. But the interesting thing is that this study looked at the insurance claims by the hospitals. So on the one hand there’s what the hospital reports publicly but on the other hand there’s the money that the hospital asks for – and they are much more honest with the money. The rate is actually about 10 times higher than that. With that higher rate, that roughly agrees with the WHO rates for most the rest of the world, which is that 6 to 10% of the people who go into the hospital will acquire a resistant antibiotic infection in the hospital. So don’t go in unless you really have to!

The bacteria that live in hospitals are almost all multiply resistant, and multiply resistant bacteria cause higher mortality and they are much more expensive to cure. So, just for example; to cure one case of non-resistant tuberculosis costs about 25,000 US dollars. To cure one case of resistant tuberculosis costs 250,000 dollars. So the total economic burden is estimated to be about 80 billion a year in the US. This is the burden of antibiotic resistance and it’s probably about 10 times higher than that around the globe. So it could be approaching a trillion dollars, it’s a big problem.

And that is a direct consequence of bacterial biodiversity. This is something that we have to deal with; they are biochemically extremely diverse. Now if you look at where the resistance is coming from, you can see here in this table that in fact a great deal of it is coming from agriculture. And I think that we have to be extremely careful about how we use antibiotics in animal food. I’m sure that this is still going on in the Netherlands, it’s certainly going on in the US. This is a way of applying antibiotics that’s sub-therapeutic, it’s a very effective way of allowing just enough of the bacteria to survive so that the resistant ones evolve. So the messages are that fungal and bacterial biodiversity are a big reserve of antibiotics and resistance genes. They evolve rapidly and, Martin has already made this comment, we only should use antibiotics when we need them, we are in a co-evolutionary race with micro-organisms and we may be losing it.

Now, what about the humans? The best study I know of human biodiversity so far, is this one, it was in Science last year. What you see here, are 928 people that are along the Y-axis in this direction. The X-axis is almost unimaginably dense; the X-axis contains 650,000 different positions that they might differ from each other in their genomes. That’s done by single nucleotide polymorphisms. They break out, as you can see, into people that are natives of Africa, Middle East, Europe and so forth. Now if you do an evolutionary analysis of this… By the way, the map on the left is the spread of humans out of Africa, which is thought to have occurred about a 100,000 years ago, and this map was constructed before this information was available.

What you can see is that there was a genetic bottleneck going out of Africa. In the Middle East the genes confirm that people who came out of Africa first settled in the Middle East. And then the first people to branch off were you guys, that went up into Europe. Then these other branches are taking people out across Asia, down into Australia and into the New World. There is a very nice confirmation written in the genes of what archaeology and the fossils tell us.

Now what happened, was people went out and spread across the planet, and became themselves biodiverse. They began to vary genetically in their ability to metabolise drugs and their ability to resist infection. The first really serious signal of this came in the late 1950s when Ciba Geigy developed a drug in Switzerland and tested it on Europeans and it was fine. They released it in Japan and it killed twelve people and it made some thousands of people sick. 

That then lead to what is now called pharmacogenomics, where we realise that inter-ethnic differences in the genome give differences in the way people metabolise drugs. Interestingly, the same gene products that are involved in metabolising drugs, are products that detoxify smoke, detoxify poisons in food and are involved therefore in susceptibility to cancer. There is considerable evolutionary information in that tree of people coming out of Africa. Understanding our own biodiversity is becoming critical for medicine.

Also written in our genes is the history of our exposure to infectious disease. The most famous of them, of course, is Sickle cell anemia and the other abnormal hemoglobins, that match the distribution of malaria. There are a few others, I’ll mention them now in the summary on medicine.

Basically, as we spread across the planet, we became genetically diverse. That changed our susceptibility to drugs and to disease. This is clinically important and the doctor actually needs to know what kind of genetic background he or she is dealing with when he prescribes drugs. There’s genetic disease resistance that’s written in our genomes and that’s for malaria and leprosy, HIV, typhoid and TB; those are the well-established ones. And actually, probably in the 21st century, we are going to see some fascinating detective work. For example on why people in Northern Europe are resistant to AIDS and why that was a pre-adaptation or ex-adaptation in some Northern Europeans, and many other such stories will develop.

We are currently co-evolving with our pathogens. I’m currently measuring selection rates on humans in Massachusetts, I can tell you that there is significant selection operating on age and maturity, downwards, and on cholesterol levels, downwards, in humans. Our pathogens and their vectors are also evolving, for example, mosquito behaviour is evolving with the use of insecticide-soaked bed nets. Basically the response of the mosquitoes if you put up an insecticide-soaked bed net, is to start biting humans during the day, when they are not sleeping. And that has started on the isle of São Tomé. So, we can expect that all of our interventions in the natural world are going to cause responses. The take-home message on this is that those other species have their own agendas and they are going to respond to everything that we do.

Now what about ecology? Wageningen has very good ecologists, there are wonderful Dutch ecologists at all the universities in Holland, and a basic issue in ecology has been whether or not stability is promoted by biodiversity. This is a theme that goes back now, I would say well into the 19th century. Is it really true that you need more different kinds of species in an ecosystem for it to provide mankind with essential functions? Will we really be at risk if we simplify the world?

Well, one of the founding pieces in the modern literature is a study by Lord Robert May, on complexity and diversity. If you look on biodiversity and ecosystem functions you can find over a thousand publications on it and of course I’m now going to summarise every single one of them for you and you will be here until late next week…

There really are some take-home messages here, that are actually fairly simple I think. Does biodiversity increase with the productivity of the ecosystem? Not does the productivity increase with biodiversity, but if you look at manipulation; to make an ecosystem more productive, will it have more species in it? And there is a pattern in the plants, and that is that you tend to get most species at intermediate productivities. Very poor ecosystems have few species, very productive ones have few species, but in the middle there appears to be a biodiversity peak.

But I think the critical question is this one: Are ecosystems redundant? Could we get all of our essential services from fewer species? We actually have very little information on this. There is a recent paper which shows that we need a diverse pollinator community to pollinate our crops. And that just having one kind of pollinator doesn’t do nearly as good a job as having a diverse community. They appear to be complementary, they compensate for each other so that if we simplify the pollinator community we could suffer major economic damage. But I must say: that’s just one aspect of ecosystem function.

There have been attempts to put dollar figures on ecosystem services. Now the thing about ecosystem services - which you can think of as things like clean air, clean water, recreational capacity, all sorts of things like that, everything that nature gives us for free – is that they are externalised, they are not captured by the market. The market doesn’t put a dollar figure on them and so they are not really weighted properly in policy decisions.

So one can ask: what is the value of ecosystem services? People like Costanza and his team have tried to estimate this. This is now about a decade ago, it has been a controversial area. But I think that for today, I just want to indicate, that one can make an estimate, and it is 33 trillion dollars a year. Now at the time the estimate was made, that was greater than the total human economic output of the planet. What that estimates basically is how much it would cost us to replace what nature gives us for free. So that, if we destroyed it, this is how much we would have to pay to get back the clean air, clean water and so forth. It’s a bit of money.

Now, that is actually estimating how large the global ‘Tragedy of the Commons’ is. The ‘Tragedy of the Commons’ is basically what happens to the collective good when it is exploited by selfish individuals. So that’s the degree to which people are not connected to their actions by paying for services that are delivered by nature. So it looks like that what we ought to be really worried about, are ecosystem services. They are very diverse. And one can think about this either in an emotional way, the way an environmental activist would think about it, with all kinds of pollution and factories spewing pollution into the skies. Or one could look at it as ‘every problem is an opportunity’, the way the political scientists have here, and they have created a Game Theory that allows them to try to solve the ‘Tragedy of the Commons’. You know, humans are endlessly ingenious and so every one of these things becomes a research programme by some academic. And, sometimes, they pay off!

Now, the economic view really doesn’t say anything about what the biodiversity is doing. It’s just saying that there is something out there that is providing this service. So, if species are highly redundant, that means if five or six species are all doing the same thing; we could get rid of three or four of them and it wouldn’t make any difference. So as a counter hypothesis I give you, a friend of mine in Paris gave me this review of redundancy; we only need 117 species. Ok? We need the cows, the sheep, the horses. We desperately need the truffles, we have to have the fungi that makes the cheese, we can’t do without the yeast that makes the beer. The Dutch would not do without their herring, and so forth. But you can see that that’s a much, much smaller number than the number of species on the planet. So if you go into a strictly hydroponics world, that’s extremely simplified, than there isn’t an economic justification – and that’s an anthropocentric view - for the beauty and the wonder of nature.

Now what about evolution? Does evolution give us any clue about the value of biodiversity? Well basically, if you look at the tree of life, you would just say; we are just one of the tips, out there, we are a relatively minor tip on a minor branch of a gigantic tree. So that’s kind of the Copernican view of earth; the small planet on the edge of a minor galaxy in a forgotten corner of the universe. We all shared ancestors with other species at one point; it’s about five to seven million years back to shared ancestors with chimps, it’s about a billion years back to sharing ancestors with green plants and about 2.5 billion back to bacteria. And you could say: Which little piece of DNA went which way down the different branches of the tree of life didn’t really endow one branch with any moral superiority to dominate the others, it’s just something that happened. No meaning. So that view from evolution, I think, doesn’t really warm your heart. It might give you a feeling of helpful intellectual relativity, but it doesn’t warm your heart.

So the agricultural view I think, is quite pragmatic; we need biodiversity for disease resistance and crop improvement and we have known that for a long time. The medical view is that biodiversity is a threat in pathogens and it’s a defence in humans. The ecological view is that diversity has benefits but the overall results are mixed when people try to look at the impact of biodiversity on ecosystem functions. The economic view is that ecosystem services would be very expensive to replace, but we don’t know how they depend on diversity. The evolutionary view is that all living things are related but there isn’t any natural value out there; value is something that humans invent and they place on nature, it is not something that nature gives to humans.

I would like to end with the intellectual view and that is that biodiversity is the source of very, very important ideas. And that when we then place a human value on diversity it is a political expression. Some people are going to spin to exploit diversity, some people are going to spin to conserve it, and we get into conflicts with each other over our different views.

So, here’s Darwin in his late age, the famous photograph. His ideas are taking a very long time to be accepted, I think this is an interesting thing to study. I actually think people in the history of science should be studying why it is that Darwin is taking longer to be accepted than Newton. They have deep implications for the human condition. His ideas are based on thinking about the consequences for variation and population, so it’s basically population-thinking rather than deterministic single-unit-thinking. And they cannot be understood at lower levels. There is a lot in modern biology that really is implicit in chemistry and physics, but evolution is not. Darwin’s ideas of natural selection and inheritance of ancestral conditions by descent are things that you will not find in physics and chemistry. And therefore they go beyond the traditional structure of the basic sciences to something new. And that also, perhaps, is a reason why they haven’t been so thoroughly incorporated.

So my parting thought is to take you back to the seven-year-old boy. And think on your children, think on your grandchildren, think of you when you were seven, staring out at the world. And the world is a beautiful and diverse place. It has Cattleya orchids and it has hummingbirds and the complexity of nature is absolutely stunning and it is a value that does not correspond to anything you can put money on. And it can be turned into something which is beautiful and is a seven-billion-dollar-a-year industry in the Netherlands.

So if you think of evolution as intellectual capital, then the ideas that are present in evolutionary biology show us that it’s a pervasive theme in biology; it unites all of biology. Some of the processes are subtle and complex, they require sophisticated analysis. And that is true from genomes to ecosystems to human brains, through all the levels of the biological hierarchy.

If we don’t provide adequate challenging training in evolutionary biology to the next generations, they are going to lack the insights they need to understand the world they live in, to understand themselves and their place in nature and to understand agriculture, medicine and the environment. This is really critical training; every major university on the planet should make sure that this is something that we give to the next generation. And that’s just as true in Leiden and in Utrecht as it is in Wageningen, where evolution is well taught, and in Groningen, where evolution is well taught and in Oxford and in New Haven.

Thank you very much.”