The scientists’ “bottleneck to breakthrough” theory posits that if global society continues to become increasingly urbanized, fertility rates decline (and eventually fall below replacement levels) and extreme poverty vanishes, then nature will have a chance to make a comeback. Not on a global scale in any of our lifetimes (those of us around today will likely be left in the bottleneck), but certainly our children’s children could inherit a much more promising world than we have today.

“It is not inconceivable that two centuries from now, the population could be half what it is today and the long-cherished goals of a world where people respect and care for nature may be realized,” the researchers write. “Espe­cially if we act now to foster this eventuality.”

The trinity here is population, poverty and urbanization.

It’s easy to see how population decline benefits nature: fewer humans means a smaller overall human footprint. Forests and other ecosystems will return; species will rebound. Such occurrences have already been seen in areas where human populations have stabilized or fallen.

Urbanization amplifies this trend. According to the researchers, urbanization not only clumps people into smaller, more efficient areas, but urban residents also tend to have fewer children. This is due to the fact that women in cities generally have more autonomy, education and opportunity, leading to fewer children. Better health care in cities also means lower infant mortality rates, resulting in couples deciding to have fewer children because they do not fear for a child’s survival.

The increasing agglomeration of humanity into cities won’t necessarily mean higher environmental impacts either, the researchers say. City dwellers tend to spend significantly more of their wealth on housing, transport and investing. They also tend to live in a more efficient system, consuming less energy and water and producing less waste per capita compared to rural communities. Today, more than half the world’s population lives in urban areas.

At the same time, the percentage of those living in extreme poverty continues to decline. While the elimination of poverty is, of course, a noble endeavor, it also arguably benefits nature as those living in extreme poverty often depend directly on exploiting nature to survive. At the same time, the researchers argue that “education, regulation, economic policy, or social norms” can help decouple rising wealth from natural resource extraction and environmental impacts.

“This piece of work is not in order to raise people’s spirits,” Walston says, “it’s because we think there is a massively underestimated or lack of awareness over these macro drivers.”

He adds that the same forces that are “driving down nature” today areforming the foundations of the ultimate circumstances [where] nature can rebound and recover.”

The scientists are by no means denying the current dire reports about wildlife and biodiversity today, but they see a potential different future ahead if we support these macro patterns, some of which are connected, ironically, to development, globalization and market forces.

“That’s the fundamental … reason why people can’t get their head around it, because, at the same time, it’s getting towards its darkest point,” Walston says.


From Japan to Sub-Saharan Africa

In May, the U.S. Centers for Disease Control and Prevention (CDC) announced that fertility rates in the country had dropped to their lowest rates ever: 1.76 babies per woman. This is well below the 2.1 births per woman that is considered replacement level, i.e. the rate at which the population holds steady. Of course, the U.S. is not going to see its actual population decline anytime soon for two reasons: built-in momentum of past birth booms, and immigration.

But the news shows that even the U.S. can’t escape the inevitability of fertility decline. As nations emerge into advanced economies, poverty declines, populations urbanize and the rate of fertility drops until eventually populations will stabilize.

The final part of this transition, actual population decline coupled with low (even non-existent) extreme poverty and high urbanization, has been observed in a number of nations, like Japan and Portugal. With fewer people, ecosystems can make a comeback.

But the political response to these demographic changes has often been negative. Concerned with short-term economic growth, politicians and economists appear to have hissy fits whenever there’s a whiff of population decline: in Japan, politicians have a history of stepping in it by blaming women for not having more kids or imploring them to become “birth-giving machines.”

The media follow the economists and politicians, though, covering population decline as some sort of natural disaster (see here and here). Such journalism decries falling fertility rates with nary a mention of climate change, the environment, mass extinction, or overpopulation. In 2017, Paul Ryan, the then-speaker of the House, implored Americans to have more children, with the father of three adding, “I did my part.”

But Walston says that so far politicians and economists, for all their hand-wringing, have been unable to find a way to reverse fertility declines: “Governments have tried everything from paying people to forcing people, and it hasn’t worked.”

The only way to really boost population, according to Walston and Sanderson, is to go to war again. It turns out peace is very good for stabilizing global population (security means you’re less fearful of losing a child), while war tends to produce baby booms.

Walston says economists “tend to go right to” the age transition in a society where demographic slowdown means more elderly than young people.

“That is a short-term — short-term meaning a couple of decades — problem for the economy. But in the long term, eventually, those old people will pass like we all do, and then the population will be smaller and the age structure will come back into more of an alignment,” he says.

There is one region that has so far bucked the global trend: sub-Saharan Africa still suffers from widespread poverty (Nigeria has more people living in extreme poverty than anywhere else) and, perhaps as importantly, a stubbornly high fertility rate. Currently, women in sub-Saharan Africa have just under five children each — twice the global average.

“I think African cities are the most important place to work on conservation or [any] other humanitarian issues because they hold the secret to stabilization,” Sanderson says.

Ongoing growth in sub-Saharan Africa makes current projections for the global population frightening, potentially as high as 11.2 billion by 2100, though Sanderson says these “bigger” numbers “take the historical rates and just project them into the future.”

He says he believes Africa will actually go through its “demographic transition a lot faster” than other regions.

For one thing, we already have the knowledge of how to improve health, welfare and education, and provide access to family planning. Second, Sanderson says he believes the region will soon see a flood of capital from outside countries, especially China, looking for new investment opportunities.

“The really critical piece is the African governments. Get those governments to work and to be trusted by their people,” he adds.

Both Sanderson and Walston point to Rwanda, where fertility rates have halved in the last 30 years, as an example of an African nation arguably coming to the edge of its bottleneck.

“You have a government that actually works,” Sanderson says. “It’s trying to make its cities work, and they’re attracting all kinds of investment, and it’s really manifesting in amazing social trends that are, again, unthought of 30 years ago.

“Rwanda is the poster child,” he adds.


Conservation in the bottle

Let’s assume that Sanderson, Robinson and Walston have hit on a correct theory: that we’re in a transitional state and that the future Earth may look far greener and smaller than the current one. What do we do with that knowledge? How do conservationists and policymakers help sustain this transition, and make sure there’s still wildlife left once we’ve all emerged from the bottleneck?

“We have this amazing challenge,” Walston says, “we have an opportunity to, over the [next] few decades, to get as much of nature through that bottleneck as possible, because whatever we do to succeed is going to be the precursor to an amazing renaissance for nature, and we’re seeing that already across the world in various places.”

According to the paper, there are five actions conservationists should focus on for nations in the midst of the ecological bottleneck: create protected areas, safeguard threatened biodiversity, support better cities, push rural-to-urban migration, and regulate destructive industries to minimize damage.

Even though different countries will experience the bottleneck at different times, the primary responses can be the same.

The number one thing is to “make sure some parts of nature do get through the bottleneck,” Walston says.

This points to an old-fashioned kind of conservation, focused on creating parks and protecting species.

“[Fortress conservation] is a highly effective, highly cost-efficient, and long-term strategy even though it’s been exactly exemplified as being the opposite,” says Walston, who describes conservation’s aim during the bottleneck as “to literally just hold on.”

“Holding on has been one of the most effective long-term strategies of conservation,” he goes on, “when you read back about those people who … established Yellowstone National Park.

“They thought that was it. They thought the West was lost.”

Walston believes if those past conservation champions saw the American West today — the return of the wolves, the rebounding of grizzlies, the reconnecting of parks across the Rockies — “they would cry with happiness.”

A focus on protected areas aligns well with another bold idea circulating in conservation circles today: Half Earth. First developed by renowned scientist E.O. Wilson, Half Earth posits that humans should set aside half of the planet for nature, both on land and water, to avoid mass extinction.

Walston says he loves the “bold statement of ambition” in Half Earth, but says he thinks the conversation has become too bogged down in minutiae and pessimism.

“[Bottleneck to breakthrough] offers us a better mechanism of achieving Half Earth than any sort of [map]-based analytical prioritization process that is coming out at the moment,” he says, adding. “Everyone at the moment is talking about the unachievability of Half Earth — and we actually think it could be way more than half.”

Walston, who began his career as a conservationist in Thailand, points to that country as informing his views and theory. “Thailand was the laughing stock. Thailand was the bogeyman in Southeast Asian conservation when I was cutting my teeth. We hit the bottom.”

But with declining poverty and fertility, increased urbanization and better governance, Thailand is “starting to come back” in nature terms, according to Walston. Now the needs of conservation in Thailand should turn to connecting the burgeoning middle class with their natural heritage, he says.

“We’ve got to connect them back to these places [to] which they feel ownership,” Walston says. “They’re the ones now who are ensuring their government pays more for these sites, does more to protect them, connects them up, allows for innovative new conservation like conservancies to work around them and to actually expand.”

Walston points out that even the tiger may be starting to make a slow rebound in Thailand, with a second population discovered in 2017.

Countries emerging from the bottleneck don’t suddenly go from losing nature to gaining it; the process is slow, taking decades, and isn’t a straight shot. But it can mean that natural landscapes get some breathing room, achieve more public support, and are less imperiled.

Walston says post-bottleneck levels of ambition should rise to making “bold commitments,” including toward establishing transnational parks, community conservation areas and interconnecting parks, and looking forward to potential rewilding.

Walston and Sanderson say their organization, WCS, is already incorporating the bottleneck-to-breakthrough theory in its daily work. There is an increased focus on urban areas at WCS, while at the same time the organization is very focused on the places where the bottleneck is the most cramped: sub-Saharan Africa and parts of Asia.

Most recently, the researchers used their theory to analyze the potential future for tigers in Southeast Asia.

Walston again points to Rwanda and how the “holding on” of gorillas there has achieved unimaginable success.

“Goodness, what Rwanda went through over the last 30 years,” he says. But “someone … held on to those mountain gorillas through all of that. Now it’s the most phenomenally successful conservation program, run by Rwandans, supported by the Rwandan government and … providing a strong financial spine to the local and national economy.”

Today, Rwanda’s mountain gorilla population is on the rise.

“At its worst moments, [conservationists] still held on. That’s the primary strategy in [the bottleneck],” Walston says.

“If anything, we see our paper as exactly the reason to work in conservation and urban planning, because our work now could have such enormous long-term payoff,” Sanderson says.



J.R.R. Tolkien invented the word eucatastrophe. It refers to the sudden, happy U-turn so common in myths and literature: the protagonist comes to the edge of total ruin and then, by some means, turns things around. Near destruction becomes happily ever after.

Tolkien employed this idea to great effect in his seminal work, “The Lord of the Rings,” but, as a Christian, he also believed in its real-life power: that even as we reach the edge of peril, humanity has the agency to reverse course.

“We are getting closer to the greatest inflection point,” Walston says of the bottleneck-to-breakthrough theory, “it’s the point where things may look the most dire.”

Walston and his colleagues’ theory is based on reams of evidence and data, but it also requires coming to particular conclusions about what they all mean. Ultimately, the theory leads to a possible prediction about our future.

It’s not destiny. It’s an idea. A tantalizing one, but it may turn out not to be true at all.

“Success is by no means inevitable,” the researchers write. “But … acting to accelerate these dynamics now offers the best opportunity humanity will ever have to recover nature on a global scale” — to, in a word, complete a eucatastrophe.

Still, the researchers acknowledge that one of the threats that could throw a wrench into everything is global warming.

Sanderson calls it a “wild card” due to arguments over “tipping points and setting up positive feedbacks that will take the Earth system a really long time to recover from.”

If we allow our climate to go over the edge, mass extinction may become inevitable.

But Sanderson also stresses that action on their theory would produce a cooler world. One of the best — and least talked about ways — to combat climate change is for societies to transition more quickly to smaller families.

Cities are also key.

“One of the underappreciated aspects of tackling climate change is urbanization,” Walston says, citing the C40 Cities climate initiative. “Forget states, forget, in many ways, federal governments, it’s the cities of the world [that] are coming together, both because they are feeling the brunt of [climate change] but also because they are feeling power.”

Still, any prediction comes up against a lot of ifs. What if the population trend in sub-Saharan Africa doesn’t follow the slowdown in the rest of the world? What if we blow past 2 degrees Celsius (3.6 degrees Fahrenheit) of warming? What if consumption and materialism overwhelm our ability to safeguard ecosystems? What if insects vanish, because we choose to do nothing?

The researchers want to make it clear that they are not advocating doing business as usual. Far from it. Nor are they saying current trends are just going to save us without anyone lifting a finger.

“One could imagine the bottleneck closing either because population grows too fast and poverty overtakes it, or because we turn our back on nature through some idea that only technology and progress will do all the work,” Sanderson says.

But he bucks against what he calls the “Twitter version” of environmental pessimism.

“Everything is going to hell in a hand-basket suggests there is no reason at all to do anything, because anything we do will inevitably fail. I think both [Walston] and I believe that creating the prospects for the future we want will be enormously difficult, but our paper suggests how it might actually happen, rather than — as so much of the conservation literature does — pointing out how things can’t or won’t work out.”

This January, a state-sponsored think tank in China announced that it expected the country’s population, the world’s biggest, to plateau within a decade. The report predicts that China will hit a peak of 1.44 billion in 2029 and then fall. Media outlets largely responded with the usual freakouts.

But make no mistake: this is good news, great news, in fact, for the climate, biodiversity and the sustainability not only of humanity at present, but for the future welfare of generations to come.

Walston and Sanderson point to one recent demographic projection that says the global population could fall to 2.3 billion by 2300 — less than a third of the current population.

“Two-point-three billion where nobody is poor and everybody has access to all the technology we already have now, plus whatever we’re going to invent between now and then: a completely different world in terms of conservation,” Walston says. “Conservation is not even the right word at that point.”

What would be the word, then? Maybe abundance. Maybe eucatastrophe.

I’ve been an environmental journalist too long to be wholly naïve about the various ecological or social theories that rise to the top. But I have a hard time disagreeing with many of Sanderson and Walston’s points.

So I find myself imagining another world from the one I inherited, one I’ll never see, but one my grandchildren’s grandchildren may awaken to: where orangutans are moving into abandoned plantations in Borneo, where lions are inhabiting new territory and people are saying “Well, what do we do about this now?”, where Sumatran rhinos are being transported back to mainland Asia, where scientists have lost track of how many North Atlantic right whale babies are born every year because there are simply too many.

A world where global temperatures are 1 degree Celsius (1.8 degrees Fahrenheit) cooler than now, where people are planting rainforests on long-fallow ground, and where wolves are howling in nearly all of the 50 U.S. states (I don’t advocate bringing them to Hawaii). This is a place where indigenous people are hunting monkeys on their legal lands in the Amazon, while someone in Cuba is breeding captive solenodons for re-release, and insects still rule the world.

There are 2.3 billion humans in this world. No one would imagine burning coal or oil for energy anymore (how primitive!). Extreme poverty is a thing of the past. Cities are towers of green, rural areas are flush with forests and fields, and wildernesses are just an hour away from almost anywhere.

I know this world is a dream, an illusion. But I also know it’s not impossible. And not only does our generation have the power to begin the eucatastrophe, but there are already forces at work we can harness. We just have to choose to do so.



E. W. Sanderson, J. Walston, J. G. Robinson, From bottleneck to breakthrough: Urbanization and the future of biodiversity conservation. Bioscience 68, 412–426 (2018). 10.1093/biosci/biy039pmid:29867252

Eric W. Sanderson, Jesse Moy, Courtney Rose, Kim Fisher, Bryan Jones, Deborah Balk, Peter Clyne, Dale Miquelle, Joseph Walston. Implications of the shared socioeconomic pathways for tiger (Panthera tigris) conservation. Biological Conservation, 2019; 231: 13 DOI: 10.1016/j.biocon.2018.12.017


Article published by Jeremy Hance
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