Climate Change: A Dialogue

An aide walks into a Republican Senator’s office. She has just finished a report on climate change and is giving the Senator a brief summary of her findings:

Aide: If we continue to burn fossil fuels, there’s a good chance we’ll cause significant ecological, political, and economic disruption. It could get very bad.

Senator: But it’s not 100%?

A: No. But–

S: Okay. Let’s keep burning fossil fuels. Otherwise, some people won’t make as much money on their investments and others might need to find new jobs.

A: Well, if we keep burning them the changes in our climate could be extremely difficult to cope with. Entire species could go extinct. Storms and droughts and wildfires will worsen and become more frequent. Millions of people could be displaced, in which case tens of thousands will surely die. Likely more. Sea levels could rise and inundate hundreds of billions of dollars in property and infrastructure. Maybe trillions. Conditions will be ripe for civil unrest, even war.

S: But it’s not 100%?

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This Changes Everything: Capitalism vs. the Climate (and Naomi Klein vs. Science)

This Changes Everything is a strange book. I agree with its central premise. Capitalism is a fundamentally flawed ideology, that, unchecked, has the capacity to cause untold social and ecological destruction. Within the bounds of the market, there are no mechanisms suitable to address climate change. The energy corporations responsible for pumping greenhouse gases into the atmosphere aren’t sensitive to the prospect of rising sea levels, more severe fire seasons, long-term drought, or more frequent and intense natural disasters. They might contain people who recognize these problems, but the ultimate arbiter of their decisions is short-term profit accumulation. Suddenly developing a social and ecological conscience – and acting accordingly – would be economic suicide. Corporations that remained responsive to the interests of shareholders would swiftly swoop in and happily gobble up the share of the energy market abandoned by their more environmentally friendly competitors.

Much has been made of finding market-friendly solutions to climate change. The idea that corporations that make billions off the extraction and production of hydrocarbons will somehow responsibly and organically respond to social and ecological threat of climate change is pure fantasy. There’s too much inertia in their current mode of production, and too little incentive for them to change it. Indeed, as Klein reports, some fossil fuels giants have tens of billions of dollars invested in future extraction initiatives. Shifting away from burning hydrocarbons would entail huge immediate blows to their bottom line.  Which brings us to Klein’s central thesis: while the burning of fossil fuels is directly linked to the increases in atmospheric carbon heating the planet, the final and ultimate cause of climate change is the profit motive and the haphazard paths followed in pursuit thereof. In this regard, Naomi Klein makes a pretty good case.

Klein’s critique of capitalism is bold and refreshing. Interestingly, it’s a point the fossil fuel industry’s most zealous advocates had seized upon well before the terms “global warming” and “climate change” had entered the popular vernacular or become the focus of intense, widespread public scrutiny. Klein reports on conferences held by organization like the the Heartland Institute and Heritage Foundation where attendees issued dire prognostications about the social, political, and economic implications of climate change. Not in terms of the direct ramifications of large-scale environmental change, mind you, but in terms of the large-scale social planning that will inevitably be needed to address them. Surprisingly often, people at these conferences accepted the reality of climate change. Many had even made peace with humanity’s role in causing it. Their concern was not whether climate change was real or not. It was if and how the reality of climate change might redefine the social order, undermining decades of neoliberal policy and the ceaseless march of privatization and deregulation. In short, they were concerned that a public tuned-in to the threats posed by a changing climate could begin to use their influence as voters to exert control over the behavior of markets – via the intermediary control of representative governance. In other words, they recognized that addressing climate change demands top-down intervention – i.e. socialism.

It’s hard to overstate the perversity and cynicism of this outlook. Recognizing that unregulated energy markets contain no mechanism for responding to the social and ecological toll exacted by a changing climate, these people are more concerned with protecting their bank accounts than working to ensure the wellbeing of future generations.

Of course, one could go too far in tarring the intentions and motivations of people so concerned about the threat of democratic socialism that they are willing to openly deceive the public about the risks associated with a changing climate. These people are unbridled greed-heads, to be sure. But deeper down, they’re also true believers, possessed of such desperate, unwavering faith in the wisdom of the invisible hand that they are willing to ride full-bore into the maw of ecological chaos, confident that, in the end, the market will provide.

It was once well-understood and widely accepted that there were bound to be economic transactions that involved variables and produced outcomes that couldn’t be accounted for in the price of goods. Recognizing the potential for markets to accumulate unforeseen costs and produce unpredicted benefits, economists advocated the use of taxes and subsidies, facultatively increasing the price of goods that are ecologically or socially harmful, reducing the prices of those that engender surprising benefits. Economists modelled markets as if they were comprised of perfectly rational, infinitely selfish, all-knowing agents as a matter of mathematical convenience. For simplicity, theorists conceived of transactions as instantaneous auctions, wherein everyone knew all the relevant information – including all the potential downstream costs and benefits, however distantly realized – and were entirely open about their values and motivations. Everyone knew everything they needed to know and no one tried to deceive anyone.

Somewhere along the line, this thinking leaped off the rails, and the market principles espoused and enumerated by the likes Smith, Pareto, Walras, Keynes, and Hayek morphed into an ideological religion. Enough people indifferent to nuance and obsessed with the myth of the self-made man read Hayek and Friedman – filtering their works through a hazy lens of Ayn Rand – that market liberalization became a religious crusade. They began to take the simplifying assumptions of economists too seriously. Instead of treating them like normative prescriptions for how things would work in perfect world, they began to treat them like divine ordinances about how things should work in the real world. Market fundamentalists and their allies have since made it their mission to shape the world into an Eden of free, unmitigated exchange – a perfect paradise for the idealized creatures of economic theory. Sadly, this is about as reasonable as setting up a game preserve for unicorns.

Their vision of utopia is one entirely divorced from the realities of human behavior and the natural world from which it emerged. In this vein, market fundamentalists have come to mirror the hardline communists ideologues the United States fought a nearly five decade cold war – punctuated here and there by intense moments of southeast Asian or central American heat – against. They’re so enamored of a romanticized ideology that they’ve been rendered blind to the unburnished strictures of reality. Decades of work in behavioral economics, psychology, sociology, and anthropology have revealed evidence that humans are irrational, myopic, parochial, tribal creatures, riddled with internal contradictions, from an awe-inspiring capacity for altruism and selflessness to a sickening taste for self-indulgence and materialism. The governing tenets of normative theories of economics have been repeatedly proven to be false. They make the modelling simpler, but lose descriptive fidelity with reality in the process.

When it comes to their personal fortunes, the people placing such fevered conviction in the benevolent providence of markets probably aren’t wrong. For them, the market will provide – at least for the time being. Incredibly wealthy and politically influential, they’ve got what it takes to ride out whatever storms (both literal and metaphorical) anthropogenic climate change might throw their way. Some of them will even likely make a tidy profit doing so. Already a market has emerged for in the insurance sector for companies interested in buffering themselves against the potential costs and disruptions that are bound to come with a changing climate. Climate change is the perfect storm for disaster capitalism (which Klein has written about elsewhere), opening the door for people to make millions off the suffering of others.

For those unfortunate enough to occupy rungs farther down the economic ladder, outlooks are considerably more grim. Market fundamentalists and their cronies in various world governments have placed so much rabid faith in the wisdom of the market that they are unwilling to budge an inch from the territory they’ve staked out on the frontiers of ideological fanaticism. Their belief that a market, sensitive only to the feedback of profits lost and profits gained, will always provide the best possible outcome for the most possible people has no more basis in reality than Karl Marx and Friedrich Engels’ visions of communist utopia. The men who flew a Boeing 767 into the South Tower of the World Trade Center had just a much justification for their belief that they’d be greeted in the afterlife by 72 virgins as a man like Ted Cruz does for his belief that a market entirely unleashed from the shackles of government oversight and regulation will maximize human flourishing.

Even without the looming specter of climate change, the idea that wholesale privatization and deregulation will benefit anyone outside a small minority of wealthy elites is difficult – if not fundamentally impossible – to justify. Markets simply don’t have the ingredients necessary to set prices that account for all the potential costs and benefits that come with production and consumption. Nor is there a compelling argument to made that, were prices thus set, humans would respond to them in a way consistent with their own long-term best interests. This crude reality alone should be sufficient to derail campaigns for endless market liberalization. Unfortunately, the zealots have sunk their claws so deep into the fabric of modern society that the precepts of unmitigated capitalism are treated like features of the divine order of the cosmos, built and bred into the marrow of social, political, and economic institutions the world over.

Now, as humanity has finally become sensitive to the full range of costs associated with centuries of barrelling growth and consumption, the need to overturn this fanaticism has grown more urgent than ever. This Changes Everything’s greatest strength is the force and clarity with which Klein makes this point, supporting it with detailed reporting and mountains of evidence.

Yet, for a book with such a compelling central thread, I was surprised by how frequently I found myself disagreeing with the author. Klein consistently evokes apocalyptic language, writing of human extinction and the habitability of the planet earth as if either is actually at stake. Climate change could spell untold human suffering and ecological devastation, but it’s very unlikely to drive the human species to extinction. Likewise, she romanticizes the primitive past and indigenous lifeways, treating pre-industrial societies like expert conservationists, living in perfect, blissful, harmony with the earth. Based on available archaeological evidence, this view is naive at best. Globalization is painted as a ubiquitous evil – never mind the fact that, inasmuch as it has contributed to climate change, it has also raised billions of people out of crushing poverty and perpetual hunger. Her treatment of GMOs, geoengineering, and nuclear power evinces a relationship to science that is more a matter of ideological opportunism than a devotion to reason and evidence.

Each of these points is worth addressing, because each entails a breed of error that does much to undermine the strength of Klein’s larger argument.

First, there’s the issue of human extinction. Klein oft references the final end of the human species, written in some onrushing future by the blind avarice and indulgence of past and present generations. Perhaps she’s being deliberately hyperbolic, but I don’t see how that level of exaggeration and emotionalism serves her point. It is disturbingly likely that the drought, biodiversity loss, superstorms, ocean acidification and sea level rise caused by unmitigated climate change could unleash a cascade of escalating disasters, each one feeding into the next, locking humanity into an endless, frantic cycle of catch-up. Klein is savvy enough to recognize how these crises will be handled within the logic of the market – profiteering and exploitation will run rampant, as a small minority reaps enormous benefits from the misery of everyone else.

Yet it is exceedingly unlikely that climate change will cause the extinction of Homo sapiens. This isn’t really much of a ray of hope – it’s entirely plausible that the compounding cycles of disaster released in the wake of worst-case-scenario climate change could reduce the human population to scattered bands living on the fringes of the high arctic, scavenging rancid scraps from the shores of poisoned seas and eating one another to survive. More probable scenarios – mass human displacement, massive social and economic inequality, bloody conflicts over bread and water, the emergence of hardcore corporate feudalism – aren’t much more appealing. But short of making the planet earth literally uninhabitable to our kind of organism (which it seems very unlikely to do) climate change will not drive humans extinct. Our facility with social learning, coupled with our capacity to store and transmit cultural knowledge from generation to generation, make us one of the most adaptable organisms to have ever existed. You’d have to look to tardigrades (water bears) or certain strains of fast-adapting bacteria for a more resilient species.

As with her dire prognostications, Klein’s approach to primitive and/or indigenous lifeways leaves much to be desired. She readily and consistently falls into Rousseau’s old trap, speaking wistfully, if not explicitly, of the wisdom and probity of the “noble savage”. There’s a sort of magnanimous racism to this kind of thinking, which I’m sure anyone given to it would be damn quick to deny. It suggests there’s something fundamentally different about “primitive” peoples, something that makes them more finely tuned to nature and equality than the rapacious scalawags that spilled out of Western Europe and the Mediterranean. This is pure rubbish. In terms of behavior, the only meaningful difference betweens industrial and pre-industrial peoples are cultural. It just so happens that Europeans happened to have inherited and modified innovations in agriculture, animal husbandry, food production, preservation, and storage – significantly conditioned by ecological happenstance – that facilitated massive population increases. Later, they became widely infected by the ideological prescription that material surplus and increase were desirable above all else.

The exact processes that led to this have been dealt with extensively. I won’t dwell on them here. Instead, suffice it to say that the concept of primitive utopia that emerged in the 19th century – persisting, in various forms, to muddy the thinking of an otherwise intelligent author in the first decades of the 21st – is a rosy-eyed fiction. Primitive societies often give credence to the Hobbesian diagnosis of a life that was “nasty, brutish, and short”. Rates of interpersonal violence are higher. Infanticide is commonplace. People die preventable deaths from injury and disease and animal attack. And, more to the precise point of Klein’s romanticism, they are hardly conservationists. Strong evidence indicates that the first Americans had a major role to play in the extinction of the North American megafauna – mammoths, saber-toothed cats, short-faced bears, giant bisons and ground sloths. In Australia, the first humans played a role in the eradication of a menagerie of bizarre giants – marsupials the size of hippos, carnivorous kangaroos, and an eight foot long tortoise, among others. In New Zealand, the Maori drove the giant moa to extinction. More prosaically, the archaeological record implicates humans in a number of resource depressions, extinctions, and extirpations. By around 1500 years ago, California hunter-gatherers around the Sacramento Valley had significantly reduced deer and elk populations. The earliest inhabitants of Easter Island introduced invasive species and over-exploited local resources, destroying the local ecology. My own research reveals a series of local depressions in steller sea lion populations in the seas around Sanak Island off the Alaska Peninsula – well before the arrival of Russian sailors – caused at least in part by human hunting.

Humans are humans, gifted with the same level of foresight, cursed with the same level of myopia, wherever they live. The idea that there has ever been, anywhere, a perfect relationship between humanity and nature (or even a clear demarcation between the two) is a point of hopeful fiction. The places where superficial appearances are otherwise relate not to the pure, uncorrupted conservationist ethos of indigenous peoples, but to a lack of technology or a sufficient resource base to sustain long-term population growth.

Globalization is a trickier beast. Free trade agreements have been disparaged across the political spectrum, often due to their perceived role in job loss. Because they make it easier for companies to outsource work to wherever they can find the cheapest employees, free trade agreements are often implicated in the decline in the availability of local manufacturing jobs. There is some truth to this – free trade agreements have resulted in job loss – but the larger reality is that, in the United States, most of the manufacturing jobs lost in recent years have gone to robots, not foreigners.

More insidiously, globalized commerce tends to increase the carbon footprint of economic endeavors and undermine localized efforts at political self-determination. As Klein notes, an increasingly globalized economy depends on the transportation of goods over longer and longer distances. This inherently entails pumping more carbon into the atmosphere, as cargo planes circle the globe and massive container ships drive through the oceans. Not only does this intensify and accelerate climate change, it also distances consumers from the direct ecological costs of their economic decisions. The already frail and unreliable tools consumers might have available to punish a local factory for producing goods in a way that damages local water and air supplies are entirely extinguished when the poisoned water and smoggy air are thousands of miles away. Throw in an international court system that allows foreign polluters to sue local governments for establishing regulations that favor cleaner businesses closer to home and the prospect for constructing sustainable, environmentally conscious markets look incredibly dim.

Klein’s solution is to refocus economies on a local level. This is all well and good, but it ignores the ways in which people in the developing world have benefitted from globalized trade. Certainly something must be done – urgently – to address the ecological costs of international commerce, but it shouldn’t be done at the cost of throwing billions of people back into poverty. Localized trade is generally a good idea: it lowers the carbon footprint of economic transactions and puts people in direct contact with the consequences of their economic behavior. But in finding a way to realize those benefits in local communities, it’s essential that we don’t fall into the trap of placing a higher premium on local lives simply as a consequence of proximity. The people who have been lifted out of poverty by global trade matter too – let’s find a way to limit the harm produced by a globalized economy without eliminating its benefits.

Which brings to my final major criticism: Klein’s selective science-phobia. She has a wealth of praise for solar and wind technology, but every other potential energy source is either greeted with the wary eye of a hardened Luddite or outright dismissed as too scary or too tainted by corporate greed to be a feasible alternative to fossil fuels. In my view, the best solutions to some of the environmental problems posed by global trade are technological. Let’s not do away with international commerce because of its large carbon footprint. Instead, let’s just do away with the large carbon footprint and power humanity’s aerial, terrestrial, and aquatic shipping fleets with clean fuels. This, of course, involves developing more and more efficient means of converting solar energy into electricity and inventing more efficient and resilient storage techniques (i.e. better batteries) – both realistic, if unrealized, prospects. It might be the science fiction enthusiast in me, but I have a hard time swallowing the argument that the solution to any of our problems will somehow involve less technology and innovation.

Klein seems to have a narrow and rigid list of technologies she considers worthy of approbation. Ubiquitously, they are those technologies that are perceived to make the most unobtrusive use of existing natural resources: wind and solar power. I don’t disagree with her that these are technologies that should be pursued with vigor. Especially not when it comes to solar power. Rather, my point of contention is with her ideologically defined disregard for any technology that involves manipulating the natural world in ways that might be trespass some vague bound of permissible use.

The most glaring example is nuclear power, which Klein brings up and dismisses repeatedly without offering any solid justifications for doing so. As near as I can tell, her concerns boil down to the fact that nuclear power seems scary, representing as it does a distillation of man’s abusive dominion and exploitation of the natural world. There seems to be an arbitrary boundary between good innovation – where humans create novel materials and systems to harness solar energy – and bad innovation – where humans create novel materials and systems to harness the energy of nuclear fission. Probably this has a lot to do with the relationship between nuclear power and nuclear weapons, in addition to the looming specter of disasters like Fukushima and Chernobyl.

Nuclear power, however, is safe. Since its invention, nuclear power has been linked to 300 deaths worldwide (and that’s a rather generous estimate). Over the same period (starting with Fermi’s discovery in 1934) coal mining has been the direct cause of 29,949 deaths in the United States alone. Globally, the count is surely much higher. The generation of energy from coal has killed 100 times more people in the United States than the generation of nuclear power has killed in the entire world.* Obviously, this doesn’t even begin to account for the colossal environmental costs of coal – even if we were to stop mining and burning coal tomorrow, the environmental toll would still be counted for generations to come.

The idea that we should dismiss nuclear power because of a few frightening accidents is patently absurd, especially when one considers the fact that technology already exists to build reactors that are inherently safe. In the 1970s, 80, and early 90s researchers at the Argonne National Laboratory developed and tested the integral fast reactor (IFR) – a reactor made safe by the very physics upon which it operates. The IFR was tested, simulating loss of coolant flow (the problem at Fukushima) and all normal shutdown options: it shut itself down, proving itself a meltdown-proof reactor.

Klein, I’m sure, would be quick to point out that there are additional hazards associated with an IFR. Some of its constituents – like liquid sodium – are inherently dangerous. Though the IFR produces less waste, it still comes with attendant waste disposal problems. These are real concerns, but they aren’t cause for a wholesale abandonment of nuclear energy. They should motivate further research, not outright dismissal. The raw reality is that every technology comes with its share of problems. Windmills kill bats and produce vibrations that disturb burrowing animals and subterranean communities. Solar photovoltaics are often produced using heavy metals like cadmium, which have the potential to accumulate in food chains. There are no perfect solutions. And, often enough, the only way to find out how good a solution is and what costs it carries is to try it out.

This is precisely the reason why I don’t see the use in taking large-scale geoengineering options entirely off the table. Researchers have dubbed these the Pinatubo Option, after a volcanic eruption that laid the seed for thinking about climate change in terms of solar radiation management (SRM). The basic idea is to ameliorate the effects of harmful greenhouse gases by pumping aerosols like sulfur dioxide into the atmosphere to cut down on the amount of solar radiation (i.e. sunlight) that reaches the earth’s surface. These are clearly last-case scenario options, but the idea that they should be automatically shunted into the intellectual dustbin because they come with a fog of unknowns – some of them likely dangerous – is truly strange.

In general, Klein is eager to steer the safest possible route, both ideologically and environmentally, eschewing all but the most well-established green technologies. Investments in nuclear power and geoengineering are risky, and therefore anathema. I used to be sympathetic to that kind of thinking – less and less so, as I grow and learn. The fact of the matter is that all human progress entails some amount of risk and uncertainty. Dealing with that fundamental fact is the flat fee that comes with living in a dynamic, vibrant society that values curiosity and exploration.


The puzzling thing about This Changes Everything is that it can simultaneously be such an incredibly forceful, scrupulously sourced argument against the perilous excesses of unrestrained capitalism and so gravely misguided when it touches on issues of human nature and the power of innovation. In the final analysis, Klein’s book is as much an ideological screed as it is a cold assessment of the facts. She meets the barking madness of free market fundamentalists with an ideological fervor redeemed only by the fact that it currently aligns with humanity’s best interests. This, of course, makes her an ally – not only to progressives, but to all humanity. She’s not wrong: capitalism, left unchecked, will devour the world.

Klein fetisizes indigenous lifestyles, exaggerating their cultural commitment to sustainability and regeneration. Low impact living is a natural outworking of forager lifestyles, not an internalized ideological commitment to perpetual balance. At the same time, she casts the Enlightenment and Scientific Revolution as Icarian follies – humanity learned too much, too fast, hungrily consuming the world’s resources in callous indifference to the potential consequences. Certainly it’s true that the fruits of the Enlightenment/Scientific/Industrial revolution have poisoned the natural world. That point is virtually inarguable. But the endless cycles of discovery, criticism, debate, and revolution they set in place are also responsible for every good thing in existence. The notion of individual human rights was an Enlightenment invention. Thanks to science, we now have treatments or cures for hundreds of terrible diseases. Our very understanding of the natural world – including the ways in which we’ve harmed it and the ways to cease doing so – are due to the scientific revolution. Klein’s most cherished ideal – sustainability – is a modern invention. It’s not a vestige of the primitive past, but a modern discovery.

Climate change is a problem. As are the underlying patterns of production and consumption. More fundamentally, the driving ethos of the industrialized West – that markets, unleashed, are pristine, unimpeachable optimality engines, spelling the best lives for the most possible people anywhere and everywhere they reach – is not only blatantly fallacious, it’s wantonly destructive. Markets are very good at some things (e.g., stimulating innovation) and very bad at others (e.g., adapting to variables that can’t be accounted for in price, or basically anything that requires even a modicum foresight about the social or environmental implications of market behavior). For those of us willing to accept this rudimentary truth, the necessity of top-down – yes, that is, socialist – intervention is obvious. This isn’t a matter of surrendering to a colorless dystopia of central-planning. It means whipping the dusty, tattered, rapidly decaying tools of representative government into shape and using them to assert our will in systems that are otherwise beyond our control.

This really isn’t a radical proposition. Within the confines of the market, few of us have the capital necessary to exert meaningful influence over the behavior of giants like Exxon and BP, but all of us will be affected by the environmental consequences of their business model. Using our powers as voters and citizens (diminished – and diminishing – though they may be) is the only viable option left to us. That’s why the efforts of the protestors at places like Standing Rock are so important. Civil disobedience is rapidly becoming our last line of defense against an economic system hell bent on devouring the world.

Nowhere in this recognition is there an obvious repudiation of the larger framework of values and methods that emerged out of the Enlightenment and Scientific Revolutions. There’s no denying that they gave us the coal-fired steam and gas fueled internal combustion engines whose exhaust is currently warming the planet. But there’s also no denying that, inasmuch scientific discovery has the power to doom us, it is also true that it is the only thing that can save us. Modernity comes with its own litany of woes. It also comes with a wealth of invisible comforts that make life today better than life at literally any other time in human history. Fewer people live in poverty or die preventable deaths. The attendant ecological problems are real and in urgent need of redress. In no way is that a matter of trading one delusional ideology for another. The truth is much deeper and far more difficult to master: there are no perfect solutions. Utopia is an illusion. It has not and will never exist. But progress is real. It’s just riddled with error and struggle, giving way to faltering improvements – each new order better than the last, but still flawed and ripe for replacement.

Such is the case with the mythological market of the rational, all-knowing, self-made man. It has its merits. Hard work and self-determination are great. Competition is a powerful engine of innovation. A market wound-up and left to its own devices is a blind behemoth. Let’s use the tools of scientific discovery and representative government to give it a little discipline and foresight.


* It might be contended that these numbers aren’t fair. More people have worked in coal than in nuclear power, so obviously more people have died in the former than the latter. I considered this, and tried to calculate per capita fatalities. Unfortunately, good labor statistics for the nuclear sector are notoriously difficult to find. That said, I gave it my best shot. Between 1934 and 2015, 1 in every 680 coal workers in the United States died of job-related illness or injury. Grossly underestimating the number of nuclear power workers (assuming that no one has ever worked in nuclear before 2015 and using the Nuclear Energy Institute’s best workforce estimates), nuclear power related injuries and illnesses in the United States have claimed the lives of 1 in every 11,111 employees. Coal has gotten safer over time. In 2015, just 1 in every 8,567 workers died. The same is true of nuclear, however: in the same year, 0 of an estimated 100,000 nuclear workers died.

God these things are long…

Here’s the book. Criticism withstanding, it’s well worth a read.

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Last Chance to See – the Sixth Extinction?

Per the advice of my fiancé, I recently took the opportunity to read Douglas Adams’ and Mark Carwardine’s book Last Chance to See. I undertook the task a little reluctantly, not because of any particular lack of interest, but because my graduate research leaves me with very little time for recreation reading. This, of course, is my excuse whenever I’m disinclined to do anything. In this regard, it has been extremely useful, since it generally relieves me of the burden of the sort of careful introspection that might be involved in actually articulating and justifying my motives – whatever they may be.

So, after several months of careful procrastination, I finally cracked the cover. Until that time, I was only familiar with Douglas Adams by reputation. This is probably a boarder-line heretical confession for anyone even marginally interested in science fiction, humanism, conservation, science, and – as I came to discover – really good prose. I don’t think it’s an exaggeration to say that, in terms of sheer wit, Douglas Adams rivals Mark Twain. Of course, the stylistic merits of Last Chance to See are merely a footnote. The real force of the work comes from its content.

Last Chance to See is a globetrotting adventure, with Adams accompanying zoologist Mark Carwardine on a trek to locate and observe a few of the endangered species list’s more prominent members. The impetus for the large work was a 1985 aye-aye hunting trip to Madagascar. Adams and Carwardine were hunting the aye-aye for purely journalistic reasons: being critically endangered (according to contemporary knowledge) the actual slaying of an aye-aye would have been grossly unethical. In any event, the 1985 Madagascar trip laid the seed for the larger work of Last Chance to See, commissioned as a companion book to the 1989 BBC radio series of the same name.

 

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An aye-aye. Illustrated by Joseph Wolf. c. 1863

Over a roughly ten month period of time, Adams and Carwardine travelled around the world documenting threatened species. On the Indonesian island of Komodo they encountered the eponymous dragon – a species of massive monitor lizard endemic to that island (and the surrounding islands of Gili Motang, Gili Dasami, Rinca, and Flores) with a population thought to number somewhere in the thousands. The portrait Adams paints is dismal. Though the komodo dragon is relatively secure (relative to other threatened species) the animals Adams and Carwardine encounter have been reduced to a tourist attraction – a spectacle for migratory herds of Western geriatrics. As Adams notes for multiple species throughout the book, this is a matter of cold pragmatism – species that pay their way through the tourist trade are less likely to have their right to life usurped by other, more profitable interests. Listed as vulnerable according to the IUCN (International Union for the Conservation of Nature), komodo dragons presently benefit from residence within an Indonesian national park, designated since 1991 as a UNESCO world heritage site.

Following their trip to Indonesia, Carwardine and Adams head west to look for northern white rhinos and mountain gorillas in Zaire. This brings them face to face with the bureaucratic inefficiency and corruption so pervasive in many African nations – the callous legacy of European colonialism. Adams, Carwardine, and crew navigate a labyrinth of bribes and crumbling infrastructure in order to find a pair of species hovering on the brink of extinction. At the time of his writing, there were less than 300 mountain gorillas in the wild. The situation for the rhinos was much worse – only 22 were known to freely (more or less) roam the savannah. The gorilla population had already reached its nadir in the early 1980s, when a bit less than 260 were thought to remain. Since then, their numbers have steadily increased, though the species remains critically endangered according to IUCN listings. The northern white rhino, on the other hand, is in much worse shape. As of 2006 there were only 4 individuals known to exist in the wild. There have been no confirmed sightings since and it is quite possible that the northern white rhinoceros, as a truly wild animal, is extinct.

In New Zealand, the author’s search for kakapos, a species of flightless parrot that famously tried to mate with Mark Carwardine’s head while shooting the 2009 follow-up to the original BBC radio series/book. Considerable hassle leads them to a pre-dawn encounter with one of but a few remaining kakapos. In China, they look for Yangtze river dolphins (baiji) – and find none. On the island of Rodriguez in the archipelago nation of Mauritius they easily locate Rodriguez fruit bats (flying foxes) and suffer the consternation of conservationists who wonder why anyone would come to look for the bats when so many of the island’s inhabitants are much worse off.

Stephen Fry watches as a kakapo attempts to mate with Mark Carwardine’s head. 

As of this writing, the kakapo is a bit better off than it was in the late 1980s, but still in pretty bad shape. The IUCN lists it as critically endangered, with a total population of around 130. The last known baiji died in 2002, though a fisherman filmed something tentatively confirmed as a river dolphin in 2007. Even so, one individual – or even a handful – does not a species make. By all practical measures, the Yangtze river dolphin is now extinct. Despite successful captive breeding programs, Rodriguez flying foxes number only a few hundred in the wild. Their IUCN status is critically endangered.

Naturally, Last Chance to See‘s coverage of endangered species is not comprehensive. The species discussed are the more charismatic representatives of what many believe to be a larger crisis in biodiversity that might even merit classification as a mass extinction. If so, it would mark the sixth such mass extinction event in our planet’s 4.54 billion year history – referred to by some by the slightly less dramatic moniker, Holocene extinction.

As the name might indicate, the Holocene extinction has been occurring since the end of the Pleistocene and the onset of the modern period of geological history known as the Holocene (roughly 11,500 years ago). It was around this time that some the more well-known prehistoric mammalian mega-fauna – woolly mammoths, giant ground sloths, smilodons (saber-toothed cats) etc. – reached their historical nadir, which, as it happens, is zero. The exact causes of their misforutune are unclear, but a number of compelling, non-exclusive hypotheses have been forwarded including a global shift to a warmer climate regime, the spread of infectious disease via human vectors, and direct human overkill1. Each of these hypotheses has some empirical basis, though the disease hypothesis hasn’t fared quite as well as its peers. The most reasonable assessment is that the late Pleistocene/early Holocene mega-fauna extinctions were the product of synergistic effects produced by the interactions between climate change and human predation with disease potentially compounding the effects of the latter two pressures.

mammoth-hunt-Old-Vero-Man-site

Since then, extinction seems to have continued more or less apace before accelerating with the onset of the industrial revolution and the associated explosion in human population. But whether this qualifies as a mass extinction or not is not entirely clear. The evidence here is not unequivocal. According to  paleontologists, the threshold for mass extinction is a loss of 75% of species over a period of 2 million years or less2. The question we face is whether or not modern species loss match these criteria in terms of magnitude (total percent of species lost) and rate (the period of time over which loss occurs). Finding an answer is a thornier problem than one might expect.

Ecological pressures do not affect species uniformly – a stress that pushes one species to the brink of extinction might have little or no impact on another. Consequently, present extinction trends are not evenly distributed. Amphibians have been particularly hard hit by modern ecological stresses, such that approximately one third of the 6,300 known species of amphibians are threatened with extinction1. But they are not alone in their plight. Depending on bio-geographic region, North American mammals have experienced a drop in species diversity of between 15 and 42%3. The numbers vary, but the overall trend is the same for every type of organism, from plants to birds – numbers are waning and the trend seems to be accelerating.

The data on the rate and magnitude of modern extinction (defined as within the last 10-13,000 years) should be distressing to all but the most callous of observers. They are not, however, on par with what has been traditionally defined as a mass extinction event. That assessment should not alleviate our alarm at the continuing loss of biodiversity. Other indices indicate that the modern rate of extinction is, if not outright massive, certainly unusual.

Another way of looking at extinction rates is to examine how much they differ from a historic baseline that reflects the average rate of extinction over a long (several million year) stretch of geologic history. In one study2, researchers attempted to conservatively assess the severity of modern extinction by comparing the minimum modern E/MSY (extinctions per million species per year) with the maximum historical baseline E/MSY. The modern E/MSY was estimated to be between 24 and 693, depending on whether extinction is measured over a 1,000 year average or in single year bins. Compared to the historical baseline E/MSY of 1.8, it would seem modern extinction rates are well in excess of what would be expected under typical conditions. As mentioned, this is an extremely conservative estimate. Other researchers4 estimate modern extinction rates are between 100 and 1,000 times greater than pre-human averages.

This can be viewed as problematic for any number of reasons, foremost among them being the decreases in ecosystem stability associated with decreases in species diversity. Ecosystems are commonly depicted as webs of interactions that connect primary producers (plants) with top predators and everything in between via complex chains of interaction. As diversity decreases, the importance of individual interactions increases4,5. For example, imagine a hypothetical big cat that preys on a species of deer, a species of peccary, and species of large rodent. Now imagine that the species of deer is driven extinct. The cat now depends on fewer prey species in order to survive. This simultaneously constrains the size of the cat population while increasing the importance of the peccary and the rodent. If one of those now goes extinct, the cost to the overall ecosystem is greater than it would have been otherwise. Though grossly oversimplified, this example illustrates how decreases in biodiversity increase an ecosystem’s sensitivity to new stresses. The less diverse the ecosystem, the greater the probability of it experiencing a shock that will result in a cascade of cataclysmic changes, up to and including potential ecosystem collapse.

The extirpation and reintroduction of wolves in Central Idaho and the Greater Yellowstone ecosystem provides an informative natural experiment in this regard. In the late 19th and early 20th century, the gray wolf was viewed as a menace. By 1926, active hunting and the practice of lacing animal carcasses with strychnine had resulted in the eradication of wolves in the Western United States. Suddenly released from the pressures associated with an apex predator, elk populations increased substantially. Unmitigated by wolf predation, elk grazing decreased recruitment of tree species and damaged riparian ecosystems6,7 with negative consequences for beavers, moose, and other species that depend on riparian habitat to survive and thrive. The reintroduction of the wolf in 1995 resulted in what ecologists refer to as trophic cascade. Without the stress of constant grazing, riparian ecosystems have bounced back, rejuvenating beneficial habitat for a range of species. Scavengers from grizzly bears to ravens have also benefited from an increase in carrion associated with wolf predation8.

Long story short, the extirpation of the gray wolf was bad for the ecosystem. Relative to the ecology of the inter-mountain west, its reintroduction has been unambiguously good.

Unfortunately, there are many in this world who only measure the worth of a thing in dollars and cents. These are people who, as Oscar Wilde put it, “know the price of everything and the value of nothing.” That is explicitly why the survival of species like wolves, mountain gorillas, and komodo dragons is largely dependent on their adoption as commodities in the tourist trade. History has hitched the world’s metaphorical wagon to the yoke of capitalism. I certainly don’t want to go all commie here, but the fact of the matter is that the driving force of capitalism is short-sighted self-interest. The market has no foresight. It is the emergent product of individuals competing to maximize their short-term interests. Because of this, not only do many fail see the costs associated with decreased biodiversity, they fail to see a reason why they should do anything about it. The primary driver of social action – monetary interest – has no mechanism by which to respond to species loss.

As the Economist recently reported, the over-exploitation of the world’s maritime resources has placed important fisheries in a position where they stand on the brink of collapse. The world’s oceans remain largely unregulated in terms of economic exploitation, both real and potential. That means agents are free to pursue their short-term interests regardless of the long-term consequences. In general, that spells disaster for an absolutely critical ecosystem that should properly be viewed as a common inheritance – not only for future generations of humanity, but for all life in general.

The oceans exemplify the “tragedy of the commons”—the depletion of commonly held property by individual users, who harm their own long-term interests as a result. For decades scientists warned that the European Union’s fishing quotas were too high, and for decades fishing lobbyists persuaded politicians to ignore them. Now what everyone knew would happen has happened: three-quarters of the fish stocks in European waters are over-exploited and some are close to collapse.

The salient feature of such a tragedy is that the full cost of damaging the system is not borne by those doing the damage. This is most obvious in fishing, but goes further. Invasive species of many kinds are moved around the world by human activity—and do an estimated $100 billion of damage to oceans each year. Farmers dump excess fertiliser into rivers, which finds its way to the sea; there cyanobacteria (blue-green algae) feed on the nutrients, proliferate madly and reduce oxygen levels, asphyxiating all sea creatures. In 2008, there were over 400 “dead zones” in the oceans. Polluters pump out carbon dioxide, which dissolves in seawater, producing carbonic acid. That in turn has increased ocean acidity by over a quarter since the start of the Industrial Revolution. In 2012, scientists found pteropods (a kind of sea snail) in the Southern Ocean with partially dissolved shells.

A storm of economic costs is brewing on the horizon, but the market – composed of people who live in the present and will likely die before the full costs are realized – has very little incentive to react. The inertia of the system may very well carry us into disaster.

There are those that might cry foul at this point, noting that extinction is a natural process. The modern loss of diversity might not be caused by man*. After all, 99% of the roughly 4 billion species that have ever inhabited the earth are extinct. Extinction, it would seem, is the rule rather than the exception. There are at least two responses to that argument. First, available evidence indicates that humans are in fact responsible – either directly or indirectly –  for a considerable amount of the modern loss in biodiversity. Humans have transformed 40-50% of the earth’s ice-free land from forest, wetlands, and prairie into pastures for domesticated animals, fields for crops, and cities, resulting in considerable habit constriction and fragmentation5. A 30% increase in atmospheric carbon, linked with industrialization, has resulted in the most rapid rates of climate change in the last 18,000 years5. Pollution is directly implicated in the extinction of the Yangtze river dolphin. Direct exploitation – in the form of poaching – is behind the likely extinction of the northern white rhino and the critically endangered status of the mountain gorilla. Only 130 kakapos remain due in large part to the human introduction of invasive species like rats and feral cats to otherwise pristine island ecosystems – a similar fate probably befell the dodo of Mauritius. The giant moas of New Zealand were hunted to extinction following the arrival of the Maori.

 

Image

Human and domesticated animal biomass vs. wild mammal biomass. Via xkcd.

The second response is the one given by Douglas Adams in a short epilogue to Last Chance to See. It is the story of the Sibylline Books. According to myth, there was once a prosperous city, its inhabitants wealthy, living a lifestyle of lavish excess and extreme comfort – able to indulge their every hedonistic whim. One day an old woman showed up at the gates carrying a bag of books. There were twelve of them, which the woman claimed contained all the knowledge and wisdom in the world – everything anyone could ever want to know about anything. She offered to sell them to the city’s inhabitants for a single bag of gold. Wanting for nothing, the citizens scoffed at this and turned her away. In response, the old woman asked for a bundle of firewood. The citizens obliged and the old woman proceeded to burn half the books.

A year later, the woman returned. Again she offered to sell her books, now reduced by half. But now the price had doubled. The city and its inhabitants were still pretty well off and quite pleased with themselves, so they turned her down. The woman burned another half of the books.

Another year passed and the woman came yet again. She made her offer: three books – one quarter of all the knowledge and wisdom of the world – for four sacks of gold. Things were taking a bit of down turn in the city – people didn’t have the extra money to spend on books – so they sent her away again. They didn’t even have any surplus firewood to offer the woman to burn her books with. Being a resourceful old lady, she shredded two of the books and set them aflame.

When she returned the next year the city and its inhabitants were pretty bad off. Times were desperate. The old woman offered to sell them the final book, the final twelfth of all the knowledge and wisdom in the world, for sixteen sacks of gold. The citizens were naturally confused by the sudden inflation – hadn’t the books been doubling in price each year? The woman explained that times were tough and that was her final offer. The citizens gathered every last scrap of gold they could find.

It barely turned out to be enough.


 

When I ponder the staggering ecological costs humanity has inflicted on the earth – the wholesale slaughter or indirect eradication of huge quantities of nonhuman biomass – I can’t help but think of it as some kind of crime. Humanity has been engaged in the ruthless elimination of other organisms for millennia, sacrificing countless individuals on the competing altars of crude self-interest and abject ignorance. It is a pattern that has accelerated in concert with industrialization, globalization, and population growth. Like the genocides humans have carried out against their own kind, is a problem facilitated by an inability to see others, if not as the same as one’s self, as nonetheless intrinsically valuable.

This brings to mind a scene from one of the Pirates of the Caribbean movies. Following the first entry those films quickly descended into absolute rubbish, but there is moment from the third entry in the series that has always stuck out in my mind. Perhaps this is a silly example, but I think it makes salient some of my feelings concerning the damage we, as a species, have inflicted – and are continuing to inflict – on the natural world. Jack Sparrow and his perpetual rival/opportunistic ally Barbossa are standing on a beach, looking at the corpse of a giant kraken, probably the last of its kind.

Barbossa remarks: “The world used to be a bigger place.”

Sparrow responds: “The world’s still the same. There’s just less in it.”

Works Cited:

  1. Wake, David B. & Vance T. Vredenberg. 2008. Are we in the midst of the sixth mass extinction? A view from the world of amphibians. PNAS. 105(1)
  2. Barnosky, Anthony D. et al. 2011. Has earth’s sixth mass extinction already arrived? Nature. 471(7336):51-57
  3. Carrasco, Marc A., Anthony D. Barnosky, and Russell W. Graham. 2009. Quantifying the extent of North American mammal extinction relative to the pre-anthropogenic baseline. PLoS One. 4(12)
  4. Chapin, F. Stuart et al. 2000. Consequences of changing biodiversity. Nature. 405
  5. McCann, Kevin Shear. 2000. The diversity-stability debate. Nature. 405
  6. Beschta, R. L. 2003. Cottonwoods, Elk, and Wolves in the Lamar Valley of Yellowstone National Park. Ecological Applications 13:1295-1309
  7. Beschta, R. L. 2005. Reduced Cottonwood Recruitment Following Extirpation of Wolves in Yellowstone’s Northern Range.
  8. Wilmers, C. C., R. L. Crabtree, D. W. Smith, K. M. Murphy and W. M. Getz. 2003.Trophic Facilitation by Introduced Top Predators: Grey Wolf Subsidies to Scavengers in Yellowstone National Park. Journal of Animal Ecology 72:909-916

* I ignored two issues in my discussion of extinction as a natural event. First, there is the sad fact that many people believe the modern ecological crisis is the work of divinity. This is entirely ridiculous and not really worthy of consideration. And, as I’ve written elsewhere, the sort of people who believe that sort of thing are the most insular, tribal, and intransigent folk imaginable. No amount of rational argument or empirical evidence is going to change their mind. Second, it is a false dichotomy to speak of events caused by human action as somehow separate from nature. Humans are as natural as anything else that has ever existed. When discussing issues like climate change and biodiversity loss, the point of the distinction is to narrow the focus to single cause: Homo sapiens. This delineation is worthwhile because, insofar as the world is suffering as a result of our behavior, we have a responsibility to do something about it.

Human phenotypic plasticity – how we succeed wherever we find ourselves

Increasingly, researchers are beginning to argue that environmental heterogeneity and long-term ecological stochasticity have sculpted a remarkable breadth of phenotypic plasticity as the primary means by which humans have succeeded in replicating their genetic material1,2. Variation in phenotypic response, it is argued, represents an adaptive solution to the problem of environmental unpredictability. Whether or not this is so is a matter to be arbitrated by empirical results – that Homo sapiens have managed to find a place in nearly every ecological niche on the planet, from the freezing Canadian Arctic to the island tropics of the South Pacific, is highly suggestive in this regard. To some degree this phenotypic flexibility is observable in physiological responses like shifting adiposity and skin tone3, though it is likely the expansive behavioral repertoire of humans provides the largest range of adaptive flexibility4. Humans cultivate social networks that ease energy flows and mitigate the reproductive costs experienced by females, who typically bear the brunt of the child-bearing load,  accumulate and modify trans-generational stores of information, use and invent tools to access previously unattainable resources, and play an active role in constructing the niches they inhabit5,6. Of course, genetic variation stills plays a role in human evolution, as illustrated by the changes that facilitate adult lactase persistence in populations with long histories of animal husbandry7. Yet it is becoming more and more evident that the primary aspect of human variation responsible for our adaptive diversity is rooted in the dynamic interplay among genetic, cultural, and ecological systems of inheritance.

Once thought to be something of an evolutionary novelty, phenotypic plasticity is now understood to be extremely common and widespread. In environments characterized by consistent spatial and/or temporal heterogeneity, phenotypic plasticity can evolve as an adaptive response to variation in selection pressures8,9. However, there is some debate concerning what exactly constitutes adaptive phenotypic plasticity and what selective pressures drive its evolution. Additionally, the apparent utility of plasticity in securing positive fitness outcomes across variable environments raises the question of why it is not a ubiquitous feature of all organisms across all environments. Adaptive plasticity can be identified where a single genotype expresses a range of phenotypes across a range of environments, provided that the range of phenotypes is shown to be heritable8. This, of course, leads a small definitional problem: establishing the boundary at which a single genotype begins and another ends is an arbitrary matter. At this point, it is unclear how well certain aspects of human variation meets this particular criterion. Phenotypic traits like adiposity and skin pigmentation show some level of heritability10,11,12 (not a qualitative assertion – there is no reason to assume this should have sociological consequences, because race, as it is popularly construed, is a social construct). If this is so, these traits would be removed from the running as plastic responses in the strictest sense, since it is a rigid – rather than a plastic – response that is inherited. However, if we take the entire human genotype and the range of phenotype it produces the fact that only 6% of identified genetic variation is between sub-groups seems to indicate that, as a species, humans are pretty damn plastic after all13. Again, we return to the problem of definition: what counts as a single genotype?

Image

Barsh, G.S. 2003

Selecting for Plasticity

Phenotypes are said to be plastic when a single genotype is seen to express multiple phenotypic states (reaction norms) across heterogeneous environments due to cues associated with the variable biotic and abiotic inputs present in said environments9. While one might be intuitively inclined to assume that this plasticity of phenotypic expression is a consequence of the pressures associated with environmental heterogeneity selecting for trait plasticity, this might not necessarily be the case. The observed plasticity could be a byproduct of some other trait, itself not directly connected to fitness outcomes8,14. For the phenotypic plasticity to be considered an adaptive trait, it must be heritable and consistently associated with positive fitness outcomes. Consequently, adaptively plastic traits should evolve in environments characterized by long-term regularity in heterogeneity. That is, relative to the lifetime of any individual, the environment(s) experienced should exhibit some degree of variability or stochasticity, but with respect to the lifetimes of multiple generations of the same organism, the heterogeneity must be encountered consistently.  Conceptually, adaptive phenotypic plasticity is the product of the same forces that produce adaptation in any other trait, with the addition of multi-generational stability in environmental heterogeneity as a condition defining selection for adaptive plasticity.

The selective conditions that produce adaptive plasticity are those that consistently (over multiple generations) sort phenotypes (and the underlying genotypes) in such a way that plastic phenotypes show a higher fitness than alternatives. Put more simply, environments where adaptive challenges vary over differing temporal and spatial scales select for phenotypic plasticity. If this is so, we arrive at the question of whether or not the environments in which humans evolved meet these criteria. Growing evidence from paleo-climatological, archaeological, and paleontological research indicates that the environments experienced by our hominid ancestors throughout much of the Plio-Pleistocene – roughly the last 5 million years – were characterized by just the sort of climatic variability that would have made the more malleable bipedal apes the more fit1,2,3,15. So, with regard to the proper evolution history – statistically significant pressures associated with a fluctuating climate – humans seem to measure up the strictures associated with the evolution of phenotypic plasticity.

Image

Donges, J.F. et al. 2011 (24)

Demonstrating Plasticity

Though sometimes difficult to construct, experimental demonstrations of adaptive plasticity have been carried out. For example, density-dependent variation in stem elongation in response to light cues in the plant species Impatiens capensis16 and changes in morphology associated with the absence of predation cues in the fish species Poecilia reticulate17 have been put forth as experimentally supported demonstrations of adaptive phenotypic plasticity. The existence – or absence – of adaptive phenotypic plasticity is often examined through the use of reciprocal transplant (also known as common garden) experiments. In such an experiment, an organism from one habitat is placed in a different habitat in order to identify whether or not it responds plastically to the new conditions. If a plant has a plastic response to light cues, it should express different phenotypes in environments characterized by differing amounts of light exposure. Ideally, the variable of interest should be tightly controlled.

For human subjects, the ability to perform manipulative experiments like reciprocal transplantation is limited by practical and ethical constraints. Researchers can’t pluck a baby from a Boston hospital nursery and swap it with a child from the highlands of Papua New Guinea to see how they react. Fortunately, the range of habitats successfully colonized by human populations makes for an excellent natural experiment, allowing researchers to apply comparative methods to examine the relationship between phenotypic expression and environmental context. That humans not only inhabit, but in fact thrive in an immense range of habitats despite sharing the majority of their genes is good evidence that humans are adaptively plastic animals. This still leaves open the question of what governs of plastic responses. Multiple mechanisms of heritability have been proposed to account for adaptive plasticity, including allelic sensitivity, regulatory loci, and specific plasticity genes14,18,  but the question of what genetic mechanisms ultimately underlie adaptive plasticity remain ultimately unresolved. For humans, it seems that the genetic architecture in question likely relates to our cognitive faculties – that is, the ability to search a landscape over the course of several generations and find adaptive solutions that are stored in an extra-genetic informational repository. That is, humans are species characterized by both genetic and cumulative cultural evolution.

Why Aren’t All Organisms Adaptively Plastic?

If organisms can evolve adaptively plastic traits in response to heterogeneous environments and nearly all environments exhibit heterogeneity on some spatial or temporal scale, this begs the question of why all organism do not exhibit plasticity in all traits18. Multiple answers can be found in the relative inflexibility of net fitness reaction norms (the most frequent response to a given environment)19, due in part to the frequently continuous nature of environmental variation, as well as the functional inter-dependence of phenotypic traits. First, the fact that selection ubiquitously acts to optimize fitness in a given environment constrains variation in fitness18. Since environments experienced by organisms tend to vary incrementally from one extreme to another, plastic responses can only be adaptive in the subset of environments where their performance is superior to alternative responses and their heritability is high. That is, a plastic response can only exhibit higher heritability and fitness than alternatives under certain conditions. In a transitional environment, the heritability of the response will be low, while in an environment distinctly different from than in which the response is beneficial, heritability for that trait will be non-existent, minimizing or completely eradicating its net fitness advantage19,20. Additionally, traits often exhibit some degree of inter-dependence. As a consequence, a plastic response that might otherwise be positive could be rendered deleterious as a result of associated changes in other important traits14. To some degree, adaptive plasticity may depend upon the functional independence of the trait in question, or at least on the relatively low impact correlated traits have on fitness outcomes.

Further limitations on the evolution of adaptive phenotypic plasticity can be found in the potential costs and limits imposed on plasticity by the environment in which the organism lives and the physical-chemical constraints levied by aspects of the organism’s physiology. Though their ultimate effect is the same (restricting the evolution and expression of adaptive plasticity) costs and limits differ in their functional mechanics21. Costs operate by decreasing the fitness of phenotypes, while limits prevent the development of a plastic phenotypic response in the first place. Maintenance costs, for example, detract from fitness in instances where the sensory and/or regulatory mechanisms upon which a plastic response depends are too energetically expensive. Lag time, on the other hand, imposes a limit on the expression of plasticity when the phenotype is unable to respond to environmental cues in a timely manner18,22. Since they have not been fully measured experimentally, the costs and limits that have been proposed as restrictions on phenotypic plasticity remain largely heuristic devices.

Conclusion

Given a prolonged association between the plasticity of response and improved fitness in consistently heterogeneous environments, phenotypic plasticity can be adaptive. Human evolutionary history seems to present just such a scenario, with frequent climatic oscillations selecting for a phenotypically plastic animal. Following our dispersal out of Africa, the challenges posed by migration between and colonization of differing habitats would have further selected for a malleable behavioral repertoire. However, the evolution of phenotypic plasticity is often inhibited by the inflexibility of mean fitness reaction norms, along with the range of possible costs and limits imposed by environmental and physiological constraints. Potentially fruitful avenues of research lie in identifying the specific heritable (genetic) mechanisms underlying adaptive phenotypic plasticity and measuring the relative importance of the various costs and limits that have been proposed as mechanisms preventing adaptive plasticity from being characteristic of all traits. With regard to humans, a complete explanation will be dependent on an understanding of the interaction between both genetic and cultural systems of informational inheritance23. Though the tractability (or lack thereof) of these questions can be discouraging, a full understanding of adaptive phenotypic plasticity depends on their resolution.

 

Works Cited:

 

  1. Wells, Jonathan C. K. 2012. Ecological Volatility and Human Evolution: A Novel Perspective on Life History and Reproductive Strategy. Evolutionary Anthropology 21:277
  2. Potts, Richard. 1998. Variability Selection in Hominid Evolution. Evolutionary Anthropology 7:81-96.
  3. Wells, Jonathan C. K. 2012. The Capital Economy in Hominin Evolution: How Adipose Tissue and Social Relationships Confer Phenotypic Flexibility in Stochastic Environments. Current Anthropology. 53(6): 466-478
  4. Sterelny, Kim2003. Thought in a Hostile World: The Evolution of Human Cognition. Malden, MA: Blackwell Publishing
  5. Odling-Smee, John. 2010. Niche Inheritance. In Evolution: The Extended Synthesis. Massimo Pigliucci and Gerd B. Muller eds. Pp. 195-207. Cambridge, Massachusetts: MIT Press.
  6. Laland, Kevin N. and Gillian R. Brown. 2006. Niche Construction, Human Behavior, and the Adaptive-Lag Hypothesis. Evolutionary Anthropology. 15:95-104
  7. Gerbault, Pascale, AnkeLiebert, Yuval Itan, Adam Powell, Mathias Currat, Joachim Burger, Dallas M. Shallow, and Mark G. Thomas. 2011. Evolution of lactase persistence: an example of human niche construction. Philosophical Transactions of the Royal Society B. 366:863-877.
  8. Pigliucci, M. 2010. Phenotypic Plasticity. Pp. 355-378. inEvolution: The Extended Synthesis. [M. Pigliucci and G.B. Muller, eds]. MIT Press, Cambridge, MA
  9. Agrawal, A. A. 2001. Phenotypic plasticity in the Interaction and Evolution of Species. Science. 294:321-326
  10. Maes, H.H.M., M. C. Neale, & L.J. Eaves. 1997. Genetic and Environmental Factors in Relative Body Weight and Human Adiposity. Behavior Genetic. 27(4): 325-351
  11. Barsh, G.S. 2003. What Controls Variation in Human Skin Color? PLoS Biol 1(1): e27. doi: 10.1371/journal.pbio.0000027
  12. Frazer, K. A., S. S. Murray, N.J. Schork, & E.J. Topol. 2009. Human genetic variation and its contribution to complex traits. Nature. 10: 241-251
  13. http://www.aaanet.org/stmts/racepp.htm
  14. Via, S. 1994. The evolution of phenotypic plasticity: what do we really know? Pp. 35-57 in L.A. Real (ed.), Ecological Genetics. Princeton University Press, Princeton, NJ.
  15. Trauth, M. H., J. C. Larrosoana, & M. Mudelsee. 2009. Trends, rhythms, and events in Plio-Pleistocene African climate. Quaternary Science Reviews. 28:399-411
  16. Dudley, S.A., and J. Schmitt. 1996. Testing the adaptive plasticity hypothesis: density-dependent selection on manipulated stem length in Impatiens capensis. American Naturalist 147(3):445-465.
  17. Torres-Dowdall, J., C. A. Handelsman, D. N. Reznick, and C. K. Ghalambor. 2012. Local adaptation and the evolution of phenotypic plasticity in Trinidadian guppies (Poecilia reticulate). Evolution 66(11):3432-3443
  18. Pigliucci, M. 2001. Phenotypic plasticity. Pp. 58-69 (chapter 5) inEvolutionary ecology: concepts and case studies [C.W. Fox, D.A. Roff, and D.J. Fairbairn, eds.]. Oxford University Press, Oxford, UK.
  19. Davidson, A.M., M. Jennions, & A. B. Nicotra. 2011. Do invasive species show higher phenotypic plasticity than native species and, if so, is it adaptive? A meta-analysis. Ecology Letters 14:419-431
  20. Ghalambor, C.K., J.K. McKay, S.P. Carroll, & D.N. Reznick. 2007. Adaptive versus non-adaptive phenotypic plasticity and the potential for contemporary adaptation in new environments. Functional Ecology 21:394-407
  21. Pigliucci, M. 2005. Evolution of phenotypic plasticity: where are we going now? Trends in Ecology and Evolution 20(9):481-486
  22. Auld, J.R., A. A. Agrawal, and R. A. Relyea. 2010 Re-evaluating the costs and limits of adaptive phenotypic plasticity. Proceedings of the Royal Society B. 277:503-511
  23. Richerson, P. J. & R. Boyd. 1999. Built for Speed: Pleistocene Climate Variation and the Origin of Human Culture. Perspectives in Ethology 13:1-45
  24. Jonathan F. Donges, Reik V. Donner, Martin H. Trauth, Norbert Marwan, Hans-Joachim Schellnhuber, and Jürgen Kurths. 2011. Nonlinear detection of paleoclimate-variability transitions possibly related to human evolution. Proceedings of the National Academy of Science. Early edition http://www.pnas.org/lookup/suppl/
    doi:10.1073/pnas.1117052108/-/DCSupplemental