Jeff Sachs on biodiversity

His new book Common Wealth devotes an entire chapter to this important topic.  Sachs writes:

The main lesson of ecology is the interconnectedness of the various parts of an ecosystem and the dangers of abrupt, nonlinear, and even catastrophic changes caused by modest forcings…It is a basic finding that biological diversity increases the productivity and resilience of ecosystems.  With more species filling more niches in a given location, a biodiverse ecosystem is better buffered against external shocks in is more adept at cycling nutrients, capturing solar radiation, utilizing water resources, and preventing the takeover of the system by single predators, weeds, or pathogens.  In other words, preserving biodiversity helps to preserve all aspects of ecosystem functions.  Removing one or more species from an ecosystem, for example, by selective harvesting of trees or fish or hunted animals, can lead to a cascade of ecological changes with large, adverse, and nonlinear effects on the functioning of the ecosystem.

Now, loyal MR readers may remember that I am genuinely uncertain how much we should worry about the loss of biodiversity.  I do know the following:

1. Many smart people who know much more science than I do are very worried about the loss of biodiversity.

2. Given that the human population has ballooned for the foreseeable future, massive losses in biodiversity are inevitable.  The question is how bad the marginal losses will be, if we do not adapt policy accordingly.

3. If I had to conduct a debate and argue that the marginal loss of biodiversity was going to be a tragedy for human beings (obviously, I can see the loss to animals, and yes I do count that for something), I would not do very well.  Yes Yana’s children won’t eat tuna and then I would sputter something about carbon and nitrogen cycles.

So OK readers, help me out.  I’ve read Sachs’s passage and I don’t think I disagree with any of the claims in it.  But I still cannot articulate to a skeptic exactly what marginal disaster will come if we do not take drastic action to preserve biodiversity.

Please use the comments to set me straight.  What exactly will go wrong?  And do not compare seven billion humans to pristine nature.  Compare seven billion humans with bad biodiversity policy to, say, five billion humans with a pretty good biodiversity policy.  What exactly is the difference?  What are these costs as a percentage of gdp? 

Please be as specific as possible; I genuinely would like to learn more.


Would an analogy help? What would happen to the economy if we wiped several businesses, even a few whole industries? After a few months/years other companies would took their places, but in nature the time necessary for replacement is tied to evolution, so we're talking about at least thousands of generations to relevant mutations create new species, depending of the niches wiped we may be talking about millions of generations. Loss of biodiversity would entail in a ecology recession that would probably be much longer than our recorded history is.

The deliberate destruction of sparrows under Mao Zedong's Great Leap Forward (1958 - 1962) was meant to eliminate a pest that ate grain seeds. Initially harvests improved, but so did the reproductive rate of the local locusts and other insects, which were now relieved of large numbers of their main predator. A famine that killed 38 million people followed.

The deliberate introduction of rabbits to Australia in 1859 has been identified as the largest single factor in the extinction of one eighth of Australia's native mammal species. The rabbits' effect on large swaths of the landscape has had direct consequences for agricultural production, since the rabbits destroy vegetation that prevents soil erosion, and regulates the water cycle.

A lesser consideration is the heart aching beauty of untouched areas: not just tropical rainforests, but places such as high mountain ecosystems, desert ecosystems, and temperate rainforests (Pacific Northwest, Tasmania, New Zealand). Zoos and parks are wonderful for teaching, but they are artificially maintained, and the loss of a species or two probably won't change the overall impact.

The interconnectivity of biodiversity means that we're not losing a species here or there, but losing the entire system. Ecology teaches us that when something is disturbed, the ecosystem moves on, and that "recovery" to an original state is often not possible.

Its not just not eating tuna, it is a loss of something of great beauty that cannot be recovered.

Another very important point re biodiversity is tha we're still learning plenty from nature. New medicines are inspired by chemicals produced by animals, new materials come from research into insect exoskeletons, new developments in robotics come from studying ant colonies.

A loss of biodiversity results in a reduced field of information from which to draw inspiration and discovery.

It would be sort of like if physicists never looked up. Sure, they'd still have plenty of things to study, and plenty of advancements left to make, but there'd be all sorts of things they'd miss out on, because they never got the chance to see them.

In my opinion, this is even worse for humanity than the loss of environmental stability associated with reduced biodiversity. Creative thought is quite possibly the most valuable commodity I can imagine, and the fewer the sources of inspiration available, the less creative thought that will occur.

Most of the millions of species on the earth are limited to one or a few places and are closely related to other nearby species. Losing them is like losing small businesses in a recession. Perhaps one of them will be the next Hewlett-Packard, but otherwise their loss will have little influence on the world.

In a dynamic economic with lots of mobility, new businesses arise quickly to take the place of extinct ones. Obviously, this doesn't happen with species. The big question is how much this matters. Is it like the loss of languages, where the loss is mainly aesthetic (and it is notable how often political ecology arguments are aesthetic, e.g., "the heart aching beauty of untouched areas")?

Or are we losing irreplacable and tremendously valuable sources of medicines, materials fabrication techniques, etc? Are we "burning many sections of the library, but preserving the best-sellers"? No one really knows.

Michael Woods, I am not so convinced of the 'inspired by nature' argument for biodiversity, for two reasons.
First, many if not most claims of 'Natura artis magistra' are more poetic than realistic. People just like to see a comparison with nature, and claiming your material is inspired by insects is a sure way to get into popular magazines. Medicins inspired by natural substances are rarer than people think.

Second, while I am sure there is a lot to learn from nature, I am not sure how much biodiversity we would need for that. If we do the worst we can to the world, there will still be more than enough ants left to learn our robotics and exoskeletons from.

What's the difference between loss of biodiversity due to human behavior and loss of biodiversity due to nature? Millions of species have gone extinct for millions of years, and yet life goes on.

This is key:

Removing one or more species from an ecosystem, for example, by selective harvesting of trees or fish or hunted animals, can lead to a cascade of ecological changes with large, adverse, and nonlinear effects on the functioning of the ecosystem.

When we think in terms of marginal changes we are implicitly assuming smooth functions, more or less predictable systems, etc. But we don't know that there are not discontinuities or sudden dramatic changes in velocity.

In other words, we don't know "exactly what will go wrong." Neither did Bear Stearns.

The chief difficulty of pricing (the loss of) biodiversity marginally would appear to be complexity. You just don't know with what likelihood any given cocktail of species loss will set off a cataclysmic chain of events (much less which specific cataclysmic chain of events). It might be reasonable to start by assuming these probabilities are monotonically increasing in diversity loss, but getting more specific than that probably takes a Ph.D. in biology and a dose of divine intervention.

I'm not so sure biodiversity cannot be created artificially, re: Craig Venter. But I agree it's best to start having a "better safe than sorry" approach to biodiversity.

One thing we should do regardless is create a databank to hold the genomes of every species. The economic/technical (i.e., non-aesthetic) value of every species other than our own is in its DNA, since only humans create and transmit learning/culture across generations.

As our knowledge grows, we will be able to exploit those genomes as we now do with the organisms themselves, finding their value for food production, energy production, medicines, etc.

We are on the verge of creating wholly synthesized life forms even today. These abilities will only grow.

Diverse ecosystems have many benefits as listed by the other posters, but that isn't the same thing as preserving individual species. In that sense, the analogy to losing a small business is a good one.

Volatility is bad.

I think the argument for bad impacts is toughest to make persuasive because it hinges on the cousin of the Law of Unintended Consequences -- the Law of Unpredictable Changes. These changes could, in total, be really really really bad, yet since they are a set of consequences that are tough to pin down, they sound...airy -- without substance.

The feeling of "not knowing" doesn't change a lot of minds, unless perhaps they are particularly able to cross-apply concepts such as the Sharpe Ratio to...our collective ecological portfolio.

Some definitions of biodiversity from a google search. When determining good vs. bad diversity policies, it makes sense to establish what biodiversity is. A definition that limits it to number of species will probably miss many of the values of biodiversity to humanity.

For instance genetic diversity within a species may promote survival of the species under changing environmental conditions (e.g. Peppered moth- genes in the population that resulted in black coloration promoted survival under polluted conditions, genes that resulted in light coloration promoted survival under conditions of better air quality). This form of diversity could be very important when dealing with crop disease.

Species diversity within a system may assist with retaining nutrients, prevention of sedimentation, maintenance of desired game or aesthetically-pleasing wildlife species, reduce risk of disease for humans (not as a source of medicines, but increased hosts for vectors-Google lyme disease/biodiversity), maintenance of desired plants species, etc.

Diversity of habitat types within an area generally promotes species diversity and at global scale different habitat type provide different services to humans (grasslands-grazing, forests-timber), partly because they contain different species adapted to those conditions.

Also, contributing to confusion is that biodiversity can be measured at different scales- local, regional, and global; and some of that may not scale up in terms of analyses.

I'm sure I've probably missed some of the variations of biodiversity. But, for all these forms of diversity some measure of economic value can be derived.

Googled Definitions of biodiversity (and there are several more variations of the same...)

Number and variety of living organisms; includes genetic diversity, species diversity, and ecological diversity.

The variety of life in all forms, levels and combinations. The term biodiversity includes genetic diversity, species diversity, and ecosystem diversity.[i]

The number and variety of different organisms in the ecological complexes in which they naturally occur. Organisms are organized at many levels, ranging from complete ecosystems to the biochemical structures that are the molecular basis of heredity. ...

The number of different species in a given habitat

The variety and abundance of species, their genetic composition, and the natural communities, ecosystems, and landscapes in which they occur.

Read a book by a real economist: the Ultimate Resource 2 by Julien Simon

To Roger Sweeney,
I eat plants and animals, breathe oxygen, am sheltered by a house partially built with wood products, and probably would have died without discovery of penicillin, so I feel pretty dependent on services provided by species other than humans.

But in defense of the idea that biodiversity of non-cultivated species offers more than reduced headaches to scientists studying nature: wheat eaters have benefited from existence of non-cultivated wild species used to create disease resistance in wheat.

Mass extinction is simply a mathematical process. Species go extinct all the time, it's just a question of how far the ripple-effect extends with each specie. Roll the dice and eventually you get a mass-event:snake eyes. Artificially increasing the extinction rate is the same as rolling the dice faster and faster. The odds on rolling snake eyes doesn't change, but the timing on when you will does.

jeo: Only one species of bee is dying off. The other ~20,000 are fine. We only even care because it's the one most used for pollination. So this isn't even an issue of biodiversity--people actually are trying to save the European honey bee because it has large economic value. In this case the interests of people are aligned with the interests of the bee. Also, similar drops in the honeybee population have occurred in the past, and were noted even in the 19th century. So likely not even caused by any recent human activities (pesticides, GMO).

Some commentators are confusing biodiversity with species loss. They are not the same. We have a (lack of) biodiversity problem when every farmer in Kansas plants the same variety of high-yield corn, and then we discover that a corn borer finds it particularly tasty. We have a species problem when the passenger pigeon goes extinct. In "Skeptical Environmentalist", Lomborg shows that the latter is a made-up problem: species are not going extinct every minute as scare headlines suggest. The biodiversity problem, however, is real. One might also worry about non-bio diversity, e.g. if all tractors burn gasoline or all computers run Windows.


I think you have misinterpreted me. Every human on this planet is completely "dependent on services provided by species other than humans." Without them we would all die.

But that fact says nothing about what the harm would be from reducing biodiversity, which was, after all, Tyler's question.

Without food, people die. Many Americans go on diets and reduce their intake of food. That doesn't mean they are starving to death.

Having said that, I think we can all agree that planting the entire Mississippi valley in the same variety of corn or wheat would indeed be a high risk strategy. Prudence would require that we "buy insurance" by preserving other varieties, or develop the tools to genetically modify the grains we have when the necessity arises.

"Is it not ironical that so many of the progressive thinkers who get exercised about the importance of biodiversity, justified at least partly by the belief that decentralized and complex networks are richer and more robust, simultaneously favor centralizing power in government, presumably leaving society poorer and less robust?"

What if a person wanted to actively use government to make society more decentralized and more robust? For example, what if somebody wanted to use government tax credits and subsidies to encourage widespread decentralized electricity production, in order to have a grid that was more robust to outages?

What if, in order to combat the threat of violent Islamists who want to use intimidation and violence to shut down speech, somebody wanted the government to provide an open ISP of last resort?

What if we wanted to try to use government to send signals that would enable anybody around the world to draw unfiltered internet access, to destroy the ability of certain other centralized governments to censor information?

All of these are active government interventions in pursuit of more decentralization.

"Given that the human population has ballooned for the foreseeable future, massive losses in biodiversity are inevitable."

It is inevitable if the state keeps on subsidizing unsustainable lifestyles. There is nothing inevitable about 6 (or 10, or 20) billion people using the land the way we do – on its face, it would seem that since energy is expensive, and clearing and maintaing structures on land is expensive, one would seek to minimize the amount of energy and land that one consumes. And we do do that to some extent – not everyone lives in a 6000 sq. ft. house with a two acre yard, and we sort of pay attention to how much gasoline we used – but we really are estranged from these costs by state intervention.

Our meat comes cheap because our crops come cheap because we pay farmers to plant them, our suburbs come cheap because our roads come cheap, and our imports from China come cheap because the state has borne a lot of the cost of ensuring that goods can get from point A to point B without hassle. Economists rand and rave about how this must be an unalloyed good – cheap transportation costs – and that the state has a proper role there, but isn't it possible to have transportation (as any good) be too cheap? And when do you know when you've gotten there?

There's nothing magical about the number 10 billion that necessitates a certain drop in biodiversity. It all depends on how far we stray from the free market. But you can be damn sure that without addressing serious issues with the "American dream" and transportation planning (somewhere to start: do we need it at all?), any artificial limits won't even come close to dealing with it. And even now, the world has already adopted the model (which the Americans in turn adopted from Hitler and the Soviets), but it's possible that change in the US might spur change elsewhere, as well.

Cyrus it's reasonable to try the argument out on the other side. But as Robert Ayers says, it's not a question of adding or subtracting individual species, but of moving from a more biodiverse to a less biodiverse state of the world.

The point perhaps is *not* to "manage." While Alan Watson's gibe is a bit empty because of his failure to name anyone, there's a plausible point if you turn it over: people who understand decentralization and resilience and problems of knowledge *should* appreciate the pitfalls of approaching the natural world as a management problem!

Where I said: Take that would that is useful for structures
I meant to say: Take that wood that is useful for structures

Randall, my suggestions are for a free market, not a planned economy like China's. The lack of information from a lack of free market trading leads to inefficiencies like that.

And I hope that the Chinese are buying these animals from those countries rather than just taking them for themselves, otherwise where are the high prices to keep these items rationed out?

Well, without going into too much I think what you are talking about are some economic problems that stem from a lack of free markets, not caused by them.

(I realize that I am conflating biodiversity and species loss, so I hope knowledgable readers will be forgiving of my intellectual sloppiness.) Biodiversity has benefits that are difficult to value. This is an unremarkable statement that has been floating around the culture for decades. Just think of the plot of Star Trek IV, in which Earth in the 23rd century was placed in mortal peril because all the whales had been wiped out. If future man had known that the whales were that important, we would of course have ensured their survival, but we came to that realization too late.

Let’s assume that there are thousands of species on the verge of extinction. A handful will be extremely valuable (e.g., leading to the cure for a deadly plague), yet we don’t know in advance which species will be the lifesavers.

The current enumeration of the world’s species is analogous to holding a portfolio of extremely out-of-the-money call options. The portfolio diminishes in value over time as options expire, i.e., as species disappear. We can renew the call options by keeping species alive, but the costs are considerable, and the benefits are not only difficult to measure, but both the time of realization and the probability of realization are unknown. (It’s safe to say, however, that the probability of this concept being accepted by environmentalists is zero!)

It's much worse than sloppiness, Steve, it's imposing assumptions that assume the problem away. The key word in the original passage is *system*. If you equate that to a situation in which you are keeping n species alive in separate little cages, you assume away the system!

The single biggest mistake in considering human effects on the environment is the assumption that we are somehow 'outside nature' or separate from the ecology.

We are not. We are a species of primate, albeit a highly developed one. We are ultimately subject to the same ecological pressures that every other species is. Whenever the population of one species becomes unsustainably out of balance with the environment a correction takes place. To take the most obvious examples, a food shortage may occur, a virulent strain of virus, parasite or predator may take advantage of the large numbers and increased density of hosts/prey, all resulting in deaths of large numbers and the correction of the population back to a more sustainable level.

Perhaps this point has been made above, but the problem to me is the definition of "marginal" destruction of biodiversity.
An ecosystem is interlinked, and wiping out a key species (marginal decrease of one) could do severe damage to the system. It is hard to do a cost-benefit analysis when the cost side is so complex. Destroying one spider species that parasites on ants perhaps has little cost, but removing the ants is likely to be expensive.
When the economic problem is complex, we usually argue for non-intervention.

Seems to me that Sachs' statement is a lot of eco-religioius mumbo jumbo. It may hold on small islands with unique species and ecosystems, but doesn't seem to hold for the rest of the planet. Human development can change a particular ecosystem and reduce biodiversity in a particular area, but it doesnt necessary reduce overall biodiversity. Sometimes human activities increase biodiversity. Clear cutting often results in greater rather than less biodiversity when a forest with little biodiversity is replaced with meadows with far more diversity. However, people often seem upset over that type of increase in biodiversity.

Also, what makes anybody think that government policies are likely to increase biodiversity. Every attempt to save the African elephant through government fiat has been a disastrous failure. Allowing people to benefit economically from the existence of the African elephant has actually helped the elephant.

I think bad government policy is far more likely to hurt biodiversity than simple increases in human population.


a. Biodiversity has been reduced by us, is being reduced by us; and the question we face is how far we should slow down that reduction, and if so where?

b. Biodiversity supports the human (and other) species as a hammock supports a relaxing human. We know that the increasing strain we put on that net is causing fibres to break at a good number of points, but we have little overall idea of which points and how far the fibres affected support us. When disaster comes it may be marginal or it may be catastrophic (and some of the fibre failures will just make the hammock feel more comfortable).

c. Minimising maximum regret suggests that it is well worth investing in finding out rapidly what we can usefully do. (The best place I know to get into that is at ). A sceptic should therefore be asked if he or she sees a better decision criterion to apply right now? Thereafter, we should be able to do cost benefit studies.

Will Schenk writes:

1) Humans are animals.

Again, from a narrow economic perspective, so what? If we all died, whose pocketbook would feel it the next day? What market sets the revealed preference of the human race for survival over extinction?

These are silly questions, of course. But for the same reason they are silly, Homo economicus is the wrong guy to ask about the value of biodiversity. Mr. Cowen's question is badly framed, and that's really about all that can be said about it.

Wait a minute.

The deliberate introduction of rabbits to Australia in 1859 has been identified as the largest single factor in the extinction of one eighth of Australia's native mammal species. The rabbits' effect on large swaths of the landscape has had direct consequences for agricultural production, since the rabbits destroy vegetation that prevents soil erosion, and regulates the water cycle.

Posted by: Matthew Wittman at Apr 6, 2008 6:45:30 AM

So it would seem that if Australia is ok then we have nothing to fear.

The marginal disaster would be system collapse. Obviously, biodiversity represents a system, not discrete species. The acceleration of extinction is what should be of concern. If we reach a point at which the acceleration accelerates beyond a capacity to recover or adapt, we in big trouble.

Someone aksed, "What's the difference between loss of biodiversity due to human behavior and loss of biodiversity due to nature? Millions of species have gone extinct for millions of years, and yet life goes on."

Bad analogy. In the mega-extinctions, enormous periods of time were involved in adaptation and evolution to a new equilibrium. The concern today is acceleration causing the rapid arrival at a point of system collapse.

1. Ecologic systems are complex so it seems reasonable to pay attention to biodiversity and try and reduce human societies negative impacts on it.

2. For the economists the crucial issue is determining which policies are likely to help species preservation and which would harm it.

3. Many biodiversity advocates have a complete lack of understanding of the very real problem of unintended consequences of government action.

They don't realize poorly thought out government actions can create negative externalities that are worse then the problem they were trying to solve.

Because government is so big and has so many resources it can cause environmental damage on a scale private action never could.

This problem goes go all the way back to provisions in the homestead act. Other examples are the western water projects, the massive pollution at DOE facilities, and the destruction of wetlands by direct government action.

Economists can play a crucial role in biodiversity preservation by

1. Assessing proposed government policy for unintended consequences / negative externalities.

2. Help structure preservation policies so that resource stakeholders are economically rewarded as a result of biodiversity preservation.

I'm going to make a good-faith effort to respond to Tyler's question. "Biodiversity" as it's usually interpreted seems to suggest that it's important not to destroy any species. While there might be a moral argument for such a policy (i.e., I can't create a whooping crane, so why do I have the right to destroy them?) it's hard to make an economic argument for biodiversity, defined broadly like this.

Instead, it makes more sense to argue that humans depend on certain kinds of wild habitat, and there are immediate costs associated with its disruption. Most notably, estuaries prevent coastal flooding and forests prevent erosion and absorb carbon dioxide. In China, for instance, the estimated economic benefit of flood mitigation from wetlands in Jilin province was $5700 / hm^2 / yr. link . I don't know how to extrapolate those numbers globally, but often wetlands are worth more as flood protection than as vulnerable developed land.

biodiversity: the variety of life in all its forms, levels, and combinations. Includes ecosystem diversity, species diversity, and genetic diversity (IUCN, UNEP, & WWF)

It seems to me that the difficulty with addressing biodiversity is that we do not understand ecological systems well enough to predict the effect of specific events, which makes it impossible to establish the risk. I am not an economist, but I am a biologist (not to be confused with an ecologist). So, I am going to restrict my comments to addressing biological points that have been made in this discussion.

from Sachs: "With more species filling more niches in a given location, a biodiverse ecosystem is better buffered against external shocks...Removing one or more species from an ecosystem...can lead to a cascade of ecological changes with large, adverse, and nonlinear effects on the functioning of the ecosystem."

Self-contradictory, to a degree, Sachs argues that ecosystems are simultaneously robust and fragile. The large, non-linear effects would only occur if a specific "hub" species were removed, assuming that ecosystems are organized as scale-free networks, which is debatable, but implied by Sachs' commentary.

Daniel wrote: "so we're talking about at least thousands of generations to relevant mutations create new species, depending of the niches wiped we may be talking about millions of generations"

Actually, niches are filled very rapidly. Think "Nature abhors a vacuum" here. If the species occupying a niches is wiped out, another species, that would have been otherwise less fit than the original, will fill it. This doesn't address the impact this would have on humans.

Nicolas wrote: "Once you lose biodiversity, it's forever (economically speaking)"

The biodiversity that we have now will be lost (i.e., the specific species and genetic diversity that we have right now). New biodiversity will arise to replace it. For example, mammalian diversity did most of its expansion very shortly after the K-T extinction (dinosaurs) Of course, the time scale for this effect is long in human terms.

karl strom wrote: "i'm not so sure biodiversity cannot be created artificially, re: Craig Venter."

This could generate new species diversity, not genetic diversity. The synthetic life people are all working with genes discovered in "natural" organisms. It also remains to be seen how viable these processes are. Currently, we are limited to replacing the genomes of existing organisms. It is also important to remember that individuals like Craig Venter, while being excellent scientists, are also great promoters of their own work. Finally, they are working on bacteria. Most biodiversity concerns involve plants and animals. Microbial diversity underpins all of our ecosystems, and we do not have a good handle human activity is doing on that front.

It is unclear what the effect of loss of species diversity will be on humans. The loss of genetic diversity among domesticated species and their antecedents can be quite important economically. Advances in quantitative genetics have demonstrated that valuable genetic variants can be found in crop lines that are themselves, as a whole organism, not a productive strain. Reduced diversity also increases the risk posed by disease (how much? we don't know).

My personal experience is that an obsessive focus on biodiversity as an end unto itself is more of a carryover of the Scala Naturae (Great Chain of Being) philosophy that motivated many naturalists in past centuries. This is based on Christian creationist thinking, which is somewhat ironic.

I have no time to read all the existing comments, but I feel obliged to leave my own.

To me biodiversity has a huge value, maybe because my childhood was in a biologically rich environment.

If I tried to be objective, I would refer to the long history of biodiversity - it has taken about 3-4 billion years to get there, and the destroyed parts do not come back quickly, although they would come faster than in 3-4 billion years (maybe in 10 million years). Now how to translate this to a monetary value, I don't know.

People may be biophilic (see E. O. Wilson's book on this). Nature has been our environment for a long time, and those who have not experienced it may not know what they have missed.

Of course there are all the points about hidden possibilities (e.g., drugs), hidden dangers (collapse), productivity vs. richness, etc., but my point is that to some people biodiversity has a huge intrinsic value.


(1) If people grow up in an artificial environment, they may not miss or value biodiversity. So we could happily destroy it without causing any harm to anybody. (You can extend this argument to favor even direr conditions.)

(2) In a sense, species are of less value than higher-order taxa, because higher-order taxa have taken longer to develop, and genetically species within, say, a genus, are almost identical. If we want to destroy species, it is best to diversify the effort evenly over as many higher-order taxa as possible.

(3) Yes, it would be hard to decide between destroying species and destroying people, and even me would probably choose to save the people. So it may be too late to save diversity, given that we need to make compromises. Maybe we should then wonder how we did get here, and could we somehow do better next time (to prevent this kind of hard choices).

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