The Invisible Brain (A Brief History of Humankind)

All thought draws life from contacts and exchanges. —Fernand Braudel

Explaining the affluence of the Northwest Coast Indians seems simple at first. They lived amid natural abundance. And abundance, after all, is affluence. Presumably that’s why so many of the affluent hunter-gatherer societies recently discerned by archaeologists lived near large bodies of water. If you want to be rich, settle on rich land.

But this explanation won’t wash. For starters, population tends to rapidly reach the "carrying capacity" of the environment. Although it’s true that an acre of Northwest territory offered more food than an acre of the Shoshone’s desert, it’s also true that an acre of Northwest territory had a lot more mouths to feed.

Granted, even on a per capita basis, a day’s work brought in more food for the Northwest Coast Indians than for the Shoshone. Bushels of fish were hauled in and packed away for winter dining. But this efficiency was due to high technologies—the massive salmon traps, the smokehouses, the storage cellar—as well as the social structures that governed them. And the technology and social structure are part of the Northwesterners’ advanced economic development—part of what we’re trying to explain when we seek the causes of affluence. To make them the cause as well as the effect would be cheating.

Besides, the Northwesterners’ affluence goes well beyond food, and thus can’t be merely the direct outgrowth of a fertile homeland. The designer robes, the spacious homes— these things don’t grow on trees.

Earlier this century, anthropologists thought it easy to explain such arduously crafted wealth as the indirect outgrowth of a fertile homeland. The key was "surplus." (This scenario assumes that the "carrying capacity" of the environment wouldn’t quickly be reached—perhaps because there’s a limit to how many hunter-gatherer can peacefully coexist in a small space.) With tons of salmon just begging to be eaten, you could meet your daily food needs in an hour or two and have plenty of time left over to weave robes and build homes. After all, such industriousness comes naturally to people, no?

Apparently not. In 1960, the anthropologist Carneiro published an influential paper about the Kuikuru, who inhabited the jungles of Amazonia and tended gardens of manioc, a staple food (once you remove the poison, which they did) and the source of tapioca. The Kuikuru could have doubled or tripled their manioc output, Carneiro calculated, but they preferred leisure time. Since then anthropologists have found various hunter-gatherer societies that, similarly, had time left over after their daily food gathering. And, as one scholar tartly put it, they "rarely spend this time designing cathedrals or in general ‘improving their lot.’ "

So much for the theory that potential surplus always equals economic development. Indeed, against the backdrop of the Kuikuru and other apparently laid-back societies, it almost seems that the conventional wisdom about the Northwest Coast Indians might be right: they weren’t examples of a general trend in cultural evolution; they were just weirdly ambitious.

If surplus isn’t the ticket to wealth, what is? What did create all the specialization and trade found in "complex" hunter-gatherer ocieties? What did the Northwest Coast Indians have that the Shoshone didn’t have? What was the key to prehistoric economic development?


Maybe we should direct these questions to a noted authority on economic development (and on non-zero-sumness, though he long predates such terminology): Adam Smith.

Two factors, Smith noted in The Wealth of Nations, are especially conducive to the growing division of labor that characterizes economic advance. One is cheap transportation. Spending your afternoon making yarn for a Chilkat robe makes sense only if the finished product can be transported at a cost acceptable to its buyer. The second factor is cheap communication. The costs of finding out what buyer want—and the cost to buyers of finding out what’s available, and at what price—have to be bearable for transaction to ensue.

Note that the costs of transport and communication apply not just to the final "purchase" of the robe—at the "retail" level—but to the links in its creation, such as getting cedar bark from the south and copper from the north. At all levels, the movement of Smith’s "invisible hand" gets smoother as information and transportation costs drop. The lower these costs, the more highly non-zero-sum the relationship among the players—the more each can gain via interaction, the more productive, per capita, the web of exchange.

How to keep these costs low if your communications and transportation technologies are primitive? One way is to stay near your customers and suppliers. In other words: live in a society with high population density. This may be the key to the wealth of the American Northwest: not natural abundance per se—an abundance quickly diluted by thick population, anyway—but rather the thick population that does the diluting. Back before communications and transportation were sufficiently high tech to catalyze markets, the stimulus came instead from a habitat that would tolerate large, close populations. And, conveniently, such habitats were often near water, which could give both technologies an added boost. Goods and data sometimes travel better by boat than by foot.

Not only were patches of the Northwest thick with people, one of whom could make blankets while a next-door neighbor focused on woodcarving; larger stretches of the coast—hundreds of miles to the north and south—were thick with peoples, the various linguistic groups that constituted Northwestern culture. Their diversity of natural resources and of cultural heritage worked in synergy. Trading for cedar bark and copper was feasible, and the robes made by drawing on local tradition struck nearby peoples as enticingly foreign.

Maybe, then, what the ostensibly carefree manioc growers of South America lacked was not driving ambition but population density. In the rain forests of the Amazon basin, settlements were small and sparse. Had there been more nearby peoples—especially peoples with handicrafts and natural resources different from those on the local menu— farmers would have felt inspired to grow more manioc for exchange.

In fact, this speculation has been confirmed. Though many scholars have cited Carneiro’s 1960 paper in dismissing the surplus theory of economic development, few have noted how Carneiro clinched his argument that manioc production in the rain forests was far below capacity: When Europeans showed up with lots of neat gadgets to trade, manioc production skyrocketed!

So, all along, the difference between native Americans of Amazonia and of the Northwest Coast hadn’t been their work ethic. The difference had been that the Amazonians weren’t getting paid to work overtime. Neither were the Shoshone. The arid Great Basin was even less conducive to thick population than were South American jungles.


Maybe we should amend Adam Smith’s trademark metaphor of the invisible hand. Smith’s point, of course, was that a bunch of far-flung people pursuing individual gain can, without really trying, collectively orchestrate a large-scale social process. The ingredients of a beautiful robe just seem to magically congregate, assemble themselves, and then find a buyer, as if guided from above.

It’s a nice image, and in ome ways apt. After all, a "hand" can do more work if moving goods is easy—if transportation costs are low thanks to the proximity of the players. Still, this metaphor gives short shrift to the other kind of cost that Smith stressed: the cost of processing data and "deciding" where the various resources should go.

Hands aren’t very cerebral, after all; guiding any invisible hand there must be an "invisible brain." Its neurons are people. The more neurons there are in regular and easy contact, the better the brain works—the more finely it can divide economic labor, the more diverse the resulting products. And, not incidentally, the more rapidly technological innovations take shape and spread. As economists who espouse "new growth theory" have stressed, it takes only one person to invent something that the whole group can then adopt (since information is a "non-rival" good). So the more possible inventors—that is, the larger the group—the higher its collective rate of innovation. All told, then, the Northwest Coast Indians outproduced and outinvented the Shoshone not because they had better brains (the sort of conclusion Franz Boas worried about) but because they were a better brain.^

The fact that population density and size lubricate economic and technological development has been largely ignored by archaeologists and cultural anthropologists. True, some of them, such as Marvin Harris, do stress population growth—indeed, some see it as the prime mover of cultural evolution. But they emphasize a different side of the growth: a downside, not an upside. "Irresistible reproductive pressures," writes Harris, have "led recurrently to the intensification of production," which in turn puts stress on the environment, leading to an ecological crisis that only new forms of technology and social organization can solve. In short: Innovate or die! Population density, in this view, drives technological and social development not by creating opportunities, but by creating problems.

This is not the place to ponder the relative importance of the "upside" and "downside" of population growth (though it is the place to suggest that the downside has been overemphasized). The key point is that these two scenarios are compatible. Even if new ideas flow mainly from the synergy of a large, dense invisible brain, environmental stress could also spur innovations—and, in any event, could make people more receptive to them. If, for example, one village, for whatever reason, had developed a serviceable salmon trap, and a means of managing it, chronic food shortage would make nearby peoples acutely receptive to the idea. Also, peoples who lacked the technology might perish, freeing up real estate for those who did adopt it. So whether or not stress often triggers the birth of technologies and social structures, it could certainly hasten their spread. To borrow some terminology from biological evolution: stress raises the rate at which cultural "mutations" proliferate; it raises the "selective pressure."

In both the upside and downside scenarios, non-zero-sumness looms large. Whether people are trying to add to their wealth or avert disaster, their rational pursuit of self-interest is leading to economic cooperation and social integration that make them better off than they otherwise would be. So either way, you expect population growth to foster upward cultural evolution. And since the human population has grown with few interruptions ever since it was human, the impetus behind cultural evolution would seem to be strong.

If this view is correct—that one way or another, more and denser population means more advanced technology and more complex social structure—then there should be a close connection between population size and density on the one hand and technological and social complexity on the other. And there is. Consider the indigenous societies that once flourished on the variously sized islands of Polynesia. The larger and more dense the island’s population, the greater its division of economic labor, the more advanced its technology, and the more complex its polity.

The story told by these and other such cultures on the ethnographic record—these "living fossils" of cultural evolution—is repeated by the archaeological record. During the Middle Paleolithic, as the human population grew slowly, the rate of technological innovation (not just the total number of technologies) also rose slowly. Then, around 40,000 year ago, both of these trends passed milestones. The human pecies was for the first time large enough to encompass the Old World, occupying virtually all inhabitable parts of Africa and Eurasia; population growth would hereafter raise population density. Meanwhile, cultural evolution reached a level that warranted a new archaeological label—the Upper Paleolithic. During the Upper Paleolithic, the average rate of technological change would be one innovation per 1,400 years, compared to one per 20,000 years during the Middle Paleolithic. Then, after 10,000 B.C., during the Mesolithic, with population growing faster than ever, the rate of technological innovation reached one innovation per 200 years (including such gifts to posterity as combs and icepicks). Hunter-gatherer societies, as we’ve seen, reached a new level of social complexity.

Of course, correlations between population size and density, on the one hand, and cultural innovation, on the other, don’t prove that population growth is the driving force. Maybe things work the other way around. Maybe cultural advances are what allow population to rise. In fact, that is undoubtedly part of the story. Take away the Northwesterners’ salmon traps (and the Big Man’s guidance of their construction and use), or the Shoshone’s rabbit nets (and the rabbit boss’s leadership), and population would have to thin out.

But that, really, is the point: technological, economic, and political development spur population even as population spurs them. In this symbiotic growth lies the inexorable power of cultural complexification. Whether you stress the "negative" side of population growth or the "positive" side—whether you stress problems or opportunities—the link between that growth and cultural evolution is one of mutual positive feedback. The more people, the more culture; the more culture, the more people.

The "negative" side of population growth—environmental stress that makes subsistence precarious—may or may not be a big part of the story, but it is certainly not the whole story. The gadgets that pile up at an ever faster rate as population grows are not just subsistence technologies. Even back during the Middle Paleolithic, more than 50,000 years ago, people were intrigued by ochres (for painting) and pyrite crystals. And, as we’ve seen, during the Mesolithic, such "prestige technologies" as jewelry became an appreciable chunk of gross domestic product.

Great effort went into getting these status symbols. They seem to have been traded over hundreds of miles, back in a time when hundreds of miles was nothing to sneeze at. Even by 30,000 B.C., long before the Mesolithic, beads made of pierced seashells were migrating 400 miles from their point of origin. Later, regular networks of exchange blossomed, linking local invisible brains to distant invisible brains. The faint outlines of giant regional brains began to form. And the driving force wasn’t periodic environmental "stress" but a more constant force: human vanity, powered by the status competition that is part of all known societies and seems to be innate.

The fitful but relentless tendency of invisible social brains to hook up with each other, and eventually submerge themselves into a larger brain, is a central theme of history. The culmination of that process—the construction of a single, planetary brain—is what we are witnessing today, with all its disruptive yet ultimately integrative effects.


Once you appreciate the importance of population size and density, the cultural gap between the Old and New Worlds starts to make sense. Twelve thousand years ago, as the occupation of the Americas was just picking up steam, population was larger and thicker back in the Eastern Hemisphere. Thereafter, so far as we can tell, the New World lagged behind the Old World in population by everal millennia—which is roughly how far the New World lagged behind the Old World in reaching early technological thresholds, such as agriculture, and early political thresholds, such as the chiefdom. (Indeed, if anything, post-agricultural social evolution unfolded slightly faster in the New World.)

Michael Kremer, an economist who stresses the link between population size and technological evolution, and who has pointed to the New World’s lagging technical level as exhibit A, has also found exhibit B. The melting polar ice caps that severed the Old and New Worlds also severed Tasmania and Australia. Tasmania’s small population promptly fell culturally behind the more numerous Australians. Modern explorers, on contacting the Tasmanians, found them to lack such Australian essentials as fire-making, bone needles, and boomerangs. Thus the four petri dishes created by the melted ice caps—Old World, New World, Australia, Tasmania—behaved in accordance with theory: larger and denser populations equal faster technological advance.

Certainly, as we’ll see, social advance can be retarded by things other than scanty population. Still, population is vital. It helps explain why we can call a people "less advanced"—the Shoshone compared to the Northwest Coast Indians, native Americans in general compared to Europeans—without insulting them.

After all, an individual Shoshone’s brain could house as much information as a European brain. A hunter-gatherer is a vast and general data bank, featuring arcane knowledge about local flora and fauna and a basic grasp of all known technology. The average European in Columbus’s day knew much less about nature, and very little about most European technology. He or she used the cerebral space thus saved by pecializing in one narrow economic task. It was the synergy of many such specialized European brains that created the technology with which Columbus and other such men intimidated Indians. Individual native Americans weren’t stupider than individual fifteenth-century Europeans—they just had the disadvantage of being Renaissance Men.

If the mutually positive feedback between culture and population were the whole story of cultural evolution, then we could end our narrative here with the words "and so on." But it isn’t. As we’ve seen, there are forbidding thresholds that got crossed somewhere between the Shoshone and modern America. Among them are the "suprafamily" threshold, crossed by the Northwestern native Americans, and the "supravillage" or "chiefdom" threshold, which the Northwesterners flirted with but may have never quite crossed.

The reason these thresholds are so dicey is that, typically, along with all the benefits of affiliation comes a loss of autonomy—subordination to a political leader. And cluster of families, like individual families and for that matter individual people, prefer autonomy to subordination, all other things being equal.

To be sure, human nature in some ways lubricates these transitions. Our species is "naturally" hierarchical in the sense that people tend to sort themselves out by social status. And the resulting facility with which leaders lead, and follower follow, has no doubt eased the evolution of social complexity. But according to modern Darwinian theory, social hierarchies didn’t evolve for the "good of the group," so follower don’t cheerfully submit to the leader for the sake of the public interest. People by nature like high status, and generally reconcile themselves to lower status only grudgingly (and temporarily, until a chance for advancement arises). Thus when any family, or any group, surrenders autonomy, submerging its identity in a larger body, subordinating itself to a central authority, some natural resistance has been overcome.

So far we’ve been talking as if economics alone can impel people across these barriers. The rational pursuit of wealth and economic security entails non-zero-sum interactions that—at least in societies which lack a currency—seem to call for political hierarchy. So political hierarchy materializes. But is the story really so simple? Can economics alone get people and groups to surrender their sovereignty? And if not, what else has helped to do that job? This is the grim subject of the next topic.

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