Charles C. Mann on Shaping Tomorrow’s World and the Limits to Growth

Charles C. Mann, author of 1491, 1493, and The Wizard and the Prophet, joins Tyler Cowen to work through the book’s central frame: the Wizard (Norman Borlaug, techno-optimist, innovate your way past limits) against the Prophet (William Vogt, carrying capacity, live within nature’s limits). They test the frame against air pollution, carbon, water, food, and population, then range back into Mann’s own territory — the pre-Columbian Americas and the Columbian Exchange.

Key ideas

1. The Wizard and the Prophet name two answers to the same question. Facing a finite planet, the Wizard — Mann’s shorthand is a ‘Schumpeterian meliorist’ — wants big, centralised, efficient facilities: nuclear power for energy, mega-scale desalination for water. The Prophet distrusts centralisation on principle and wants smaller, networked systems: solar and wind rebuilding the grid, conservation over construction. Mann’s own view: both bets are, from today’s technology, ‘equally impossible’ — a leap in the dark either way.
2. Whether an ecosystem is even a ‘system’ is the unsettled premise underneath the whole debate. Mann poses it directly: is an ecosystem ‘an actual system with an integrity of its own, with rules of its own that you violate at your peril’ — the founding assumption of environmentalism — or is it ‘more like an apartment building’, a contingent bunch of tenants sharing a few pipes? He credits ecologist Dan Simberloff with a career spent dismantling the elegant models that would answer this, and concludes ecology has not settled it. The answer decides how much room humanity actually has.
3. A shrinking, ageing population is a bigger unknown than an exploding one. Demographers expect world population to level off near 10 billion this century — not double again. But the age structure that produces is unprecedented: the population pyramid becomes a ‘cylinder’, with a shrinking base of workers under an ever-larger cohort of retirees pushing to delay retirement rather than shorten it. Mann agrees with Tyler Cowen’s colleague Robin Hanson that this, not overpopulation, may be the more serious demographic problem.
4. Pessimists can be right and still be beaten — by irrelevance, not refutation. Malthus and Ehrlich were technically correct that the earth is finite; they simply misjudged where the limit sits. Mann’s test for declaring the argument settled: if population levels off around 10 billion and everyone can be fed and housed in reasonable comfort by roughly 2070, ‘the optimists can declare victory, even though the pessimists could still be right in that there are limits. They just aren’t relevant.’
5. The Amazon basin held far more civilisation than the ecological orthodoxy allowed. For most of the twentieth century, researchers such as Betty Meggers argued tropical soil was too poor to support complex societies — a claim environmental groups then adopted as a reason to protect the rainforest from development. Brazilian archaeologists working from the 1990s onward, notably Michael Heckenberger’s work on the Xingu, found networked cities wherever they seriously looked — a direct extension of the pre-Columbian population revisionism at the heart of Mann’s 1491.
6. Cortez’s conquest of the Aztecs was political genius, not military superiority. Pushing back on the standard ‘few Spaniards beat a mighty empire’ story, Mann argues Cortez won by uniting the many peoples the Aztec Triple Alliance had subjugated and terrorised into a single army — then hijacking the result, an achievement he ranks alongside Napoleon’s hijacking of the French Revolution.

Content

The Wizard and the Prophet

Asked how to think about the solution to carbon emissions, Mann introduces the book’s organising pair. The Wizard wants big, centralised, super-efficient facilities — in practice, nuclear power. The Prophet — ‘typical environmental movement’ — distrusts giant centralised systems on principle and wants smaller, networked ones: a rebuilt grid running on solar and wind, plus extensive planting. Mann declines to pick a side: both routes are, given today’s technology, equally speculative.

Cowen presses him with his own published argument — that falling demand in rich countries just lowers fossil-fuel prices and someone else burns the difference, so total carbon flow barely changes (a Jevons-paradox effect). Mann agrees it is a strong argument, then lists reasons it might still be wrong: a growing popular habit of treating carbon dioxide as ‘pollution’ alongside particulates, which could bundle carbon controls in with smog controls in places like China; and a surprising public appetite for collective action at the city and regional level, even where international coordination remains weak.

On carbon capture and storage specifically, Mann is sympathetic to the technology despite environmentalist hostility to it, on the grounds that India and China cannot simply write off newly built coal infrastructure — carbon capture may be the only route that lets them keep it while cutting emissions. He is more sceptical of geoengineering’s institutions than its science: solar radiation management is cheap enough that a single rich individual, or a small nation such as Indonesia (which he notes has roughly seventy billionaires), could unilaterally attempt it — what economists Weitzman and Wagner call the ‘free-driver problem’.

Water: a solved technical problem, an unsolved social one

Mann agrees that water problems are, in principle, ordinary economics — pricing, property rights, targeted regulation. The obstacle is that ‘people are not rational about water’: when it feels threatened, the instinct is to build, not conserve. He cites roughly 70 per cent of the world’s water going to agriculture, up to 70 per cent of that lost to inefficient irrigation — pushing towards half the world’s fresh water wasted outright — set against nations like Israel and California building expensive mega-desalination projects regardless.

Israel is his worked example of Wizard and Prophet oscillating within one country: first the National Water Project, a huge canal channelling water from the wetter north down into the Negev Desert (which then strained relations with neighbours, since Israel had taken some 70 per cent of the Jordan River’s water), then a conservation swing into drip irrigation and desalination — both, he notes, technologies Israel imported and perfected rather than invented. Once desalination succeeded, the old ‘every drop counts’ conservation messaging disappeared outside the south. On privatising water utilities, Mann calls it underused given how badly governments have run water systems, but flags the real difficulty: private operators need to be paid back, and when governments fail to cover the difference, the burden lands on individual customers — in parts of China, a quarter to a third of household income.

Feeding the world and the search for a fixed factor

Population has kept rising and food has kept pace, against most historical predictions. Cowen asks whether there is a hard limit. Mann’s answer resists a clean one: the earth is obviously finite in some sense, but where the limit sits is essentially unknown. The environmental movement’s founding claim — carrying capacity, ecological limits, planetary boundaries, however labelled — asserts fixed points that cannot be crossed. Mann traces one of the earliest calculations to physicist Warren Weaver, who took usable solar energy as the limiting factor and found it, on that measure, effectively inexhaustible; overcrowding, not energy, would stop growth first.

This is where Mann poses what he treats as the deepest open question in the whole debate: is an ecosystem ‘an actual system with an integrity of its own, with rules of its own that you violate at your peril’ — or closer to ‘an apartment building’, a shared space rather than a bound organism? He compares ecology’s difficulty here to macroeconomics — both study huge systems with countless moving parts that nobody fully understands, both are ‘partisan and poorly understood’, and both run on models people believe far more strongly than the models have been empirically tested. He credits Dan Simberloff with a career of dismantling elegant ecological models one by one, and concludes the question is genuinely unresolved: if nature is instrumental and rearrangeable, humanity has much more room than it thinks; if the overarching cycles ecologists intuit are real, it has less.

Asked to name a leading candidate anyway, Mann offers water — there is not that much fresh water on the planet — while declining to endorse it as the answer. He is unpersuaded that topsoil is the limiting factor: erosion estimates rest on the decades-old ‘universal soil loss equation’, which measures soil movement rather than net loss (soil blowing from one farm to a neighbour’s counts as erosion on both sides). Soil contamination, by contrast, he treats as a more plausible constraint, citing Wageningen University estimates that roughly a third of the world’s arable land carries some contamination.

On when to declare the historical argument settled, Mann reframes the pessimist/optimist dispute as one of relevance rather than truth. Malthus, and later Paul Ehrlich, were correct that a finite world has a ceiling; they were wrong about where it sits. If demographers are right that population levels off near 10 billion this century — not doubling again — and if everyone can be fed and comfortably housed by around 2070, then, in Mann’s view, ‘the optimists can declare victory, even though the pessimists could still be right in that there are limits. They just aren’t relevant.‘

Demography: the cylinder no one has faced before

Cowen raises Robin Hanson’s worry that shrinking, low-fertility populations (Italy near 1.3, Singaporean Chinese near 1.1) may be the more urgent problem: fiscal strain, thinner aggregate demand, less creativity. Mann agrees this is a genuinely novel challenge. The historical ‘population pyramid’ — few older people, many younger ones supporting them through taxation — is turning into something closer to a cylinder, an age structure with no precedent in human history. He adds a wry self-indictment: people his own age want to push retirement down, asking an ever-shrinking younger cohort to support them for longer, following the European pattern. His only offered upside is that if enough older people keep working past retirement, it may buy time before automation shrinks the amount of paid work available — half-jokingly deferring to ‘robots’ as the eventual saviour.

On population control as an environmental tool, Mann is blunt: it has ‘had such a terrible record’ once embraced by the ecological elite and governments in India and China. On China’s one-child policy specifically, the demographic evidence he trusts suggests its effect on the actual population trajectory was negligible — most of the fertility decline predates the policy — while its effect on individual families was severe. His conclusion: ‘empowering women and educating women is actually what you really want to do,’ not coercive control.

Back to the New World: population, disease, and conquest

Returning to Mann’s own scholarship, Cowen asks whether Napoleon’s sale of Louisiana — and the chain running to Indian removal and the Civil War — makes Napoleon indirectly responsible for the collapse of Native American civilisations. Mann rejects the premise: smallpox epidemics documented in Elizabeth Fenn’s Pox Americana had already devastated these populations in the 1780s, with mortality estimated at 40–50 per cent, well before Napoleon’s decision. Settlement would likely have proceeded regardless; Andrew Jackson’s conduct toward the Choctaw (allies who felt betrayed after 1812) remains a separate moral failing.

On the Amazon, Mann describes a scholarly consensus overturned within his own working lifetime. Nineteenth- and twentieth-century researchers, notably Betty Meggers, argued tropical soils were too poor to sustain complex civilisation — a claim later adopted by conservationists as a reason to leave the rainforest undeveloped. From the 1990s, Brazilian archaeologists (and Americans such as Michael Heckenberger, working on the Xingu) found networked settlements resembling garden-city plans wherever they seriously searched. Living standards, Mann suggests, were plausibly good — food and water were abundant, even if protein was scarcer than in temperate regions — though material culture is hard to assess archaeologically without stone or metal artefacts to survive.

Asked about the Spanish conquest of the Aztecs, Mann rejects the ‘small band of Spaniards defeats a mighty empire’ framing outright — it was not a small force. The underrated factor, in his view, is that Cortez was a political genius more than a military one: the Aztec Triple Alliance had brutalised and subjugated many surrounding peoples, and Cortez knitted their resentment into an army large enough to topple the empire, then took the result for himself — a manoeuvre he compares to Napoleon’s hijacking of the French Revolution.

Production function

Asked how he sustains such range without a university post, Mann credits three things: no meetings (the overhead he associates with academic jobs), library access through the University of Massachusetts and neighbouring colleges, and scholars’ near-universal willingness to talk at length to an outsider with a plausible question. His stated edge is simple — reading quickly and without fear of numbers — paired with a habit from his father: stare at something long enough, ask enough questions, and the gist comes.

See also

• Tyler Cowen
• Joel Mokyr
• Joel Mokyr on Clans, Corporations, and a Culture of Growth
• Brad DeLong on Intellectual and Technical Progress
• William MacAskill on Effective Altruism, Moral Progress, and Cultural Innovation
• Carl Zimmer on the Hidden Life in the Air We Breathe
• Abundance (book)
• Bryan Caplan on Learning Across Disciplines