Tag Archives: Americas

The Great American Interchange

2.87 – 2.72 million years ago

For most of the last 100 million years, South America was an island continent, like Australia, with its own peculiar mix of species, largely isolated from other continents (although monkeys, and guinea pig relations, rafted across.) By contrast, North America was intermittently connected with Eurasia and exchanged species off and on. South America supported a rich array of marsupials, including a marsupial version of a saber-toothed tiger. It also had predatory flightless “terror birds” that seemed bent on reoccupying the two-legged predatory dinosaur niche.

terror bird

There was also a profusion of notoungulates (probably distantly related to hoofed animals in North America and Eurasia), and liptoterns. (Below is a reconstruction of a late surviving liptotern, Macrauchenia, looking like a Dr. Seuss invention.)

South America was close enough to North America for the two continents to start exchanging species by 14 million years ago, but the really massive exchange began with the establishment of the Isthmus of Panama, and climate changes, about 3 million years ago. 38 genera of land mammals walked north from South America. 47 genera walked south from North America. So the initial exchange was unbalanced; the subsequent evolution was even more so. Only a handful of South American invaders – notably armadillos and (for a while) ground sloths – succeeded in establishing themselves in North America, while North American invaders generated a profusion of new species. Many of the really distinctive South American forms would go extinct over the next millions of years.

Paleontologists dispute the causes of the turnover, but it looks an awful lot like North American species had a competitive edge. This is one instance of a phenomenon we’ve seen already in animal evolution, and will see again in human history, of large land areas generating more competitive forms.

Land of thoats

There’s a great expansion in the diversity of horses in the mid-Miocene, especially horses that are adapted to grazing rather than browsing. The shift to grazing is going on world wide among many different groups. In South America the big grazers are the liptoterns, ungulates not closely related to horses that evolve to look a lot like them, with high-crowned grazing teeth, single-toed hoofed feet and legs built for speed. (Edgar Rice Burroughs took the name thoat – what his characters rode around on on Barsoom/Mars — from one genus of liptotern, Thoatherium.)

Thoatherium reconstruction

We often think of evolution as a matter of organisms adapting to their environments, but when the environment is other organisms, each side may be chasing a moving target. Or sometimes the sides may reach an equilibrium. In the case of grazing animals, there’s a process of coevolution that goes on between grazers and grasses. Where grazers are active, the plants that survive are grasses, which keep leaves above the ground but grow from underground. And this works in the other direction: in moderately dry climates, grasses are more productive than taller brushy plants, so it’s when grasses take over that there’s enough food around for grazers – a mutually reinforcing cycle. With drier climates from the mid-Miocene on, grasslands and grazers get to be more and more important.

So a lot of the story of life on Earth is not just the appearance of this or that cool animal, but also the evolution of ecosystems. At the same time grasslands were spreading on land, for example, kelp forests were spreading in coastal oceans. We’ll see how important grasslands are in human evolution and history. And kelp forests, with their rich fish populations, might have been important too, as the highway that the earliest Americans followed along the Pacific coast to the New World.

Slava Ukraini

February 24, 2022, and after.

Russia’s attempted seizure of Ukraine this year, and the ensuing ongoing war, crystalized a new international division. This division runs deeper than the machinations and miscalculations of one autocrat. A recent report, A World Divided: Russia, China and the West, summarizes the current global divide in political attitudes. Some major findings:

Compare positive versus negative attitudes to Russia …

to China …

and to the US.

The last map is a near mirror image of the first two. Together the maps depict a world split in two, a Western / maritime rimland and an Old World heartland. 

And the division reflects a deeper divide in politics …

and social attitudes …

The division in attitudes between the West and the two Eurasian powers has developed only recently, but it has roots that go back for centuries. At least this is consistent with the thesis of a recent book, The Deep Roots of Modern Democracy: Geography and the Diffusion of Political Institutions. The authors present a modern data-driven version of an old argument, that maritime trade and naval power foster liberal, constitutional, and democratic government. Where access to the sea and trade was limited, autocracy was (and is) more likely to prevail. Also, maritime zones tend to smaller political units – city states and nation states (albeit sometimes with overseas colonies) – while more land-based zones, riverine and steppe, tend to sprawling multinational empires. Here is a map (from an earlier article by the authors) of one set of underlying geographic determinants: natural harbors. 

And here is their causal model:

Natural harbors, plus other factors in European history (here are a few from this blog), have fostered democratic development in some parts of Europe, and Europeans have brought democratic institutions with them as they have moved overseas (albeit sometimes democracy for whites only).

The appeal of a particular set of Western, and specifically Anglo-American, ideals – individualism, constitutional government, national self-determination – is broad but not universal. They developed in a particular geographic and historical context. A large portion of the world does not (pace the American Declaration of Independence) hold these ideals as self-evident truths, and even regards them (not always entirely without reason) as a mask for cynical power politics. 

And so The End of History is unfinished work.

Baby boom

June 1961 – September 1965

Malthusianism does a pretty good job of capturing the facts of life for our species before the Industrial Revolution. For example, Malthus plus standard economics helps account for some of the historic differences between wheat and rice growing societies. And Darwinism suggests the reason why Malthusianism holds for living things in general: within a population, variants with a higher intrinsic rate of increase tend to replace those with a lower rate, even if the eventual outcome is overpopulation and misery for all. So the field of human behavioral ecology, based on the assumption that people try to maximize fitness, does pretty well in accounting for behavior in pre-modern societies.

But Malthusianism, and the assumption that people are fitness-maximizers, don’t work very well for modern societies. Even as life expectancies and standards of living have been increasing around the world, fertility rates have been declining, falling below replacement levels even in many less developed countries (although rates remain quite high in Sub-Saharan Africa.) The United States mostly follows the general trend, with a long decline in fertility rates over several centuries.

And then there’s the Baby Boom: Birth rates in the United States went up dramatically following the Second World War, then reached a peak in 1957, and continued high into the early 1960s. Young people were marrying early, and having more children. Women were staying out of the workforce to take care of the kids.

baby boom

Here are two popular theories of why the Baby Boom happened that don’t work:

Soldiers coming home. The return of soldiers from the Second World War contributed to an early spike in the birth rate (visible in the chart above in the late 1940s). But the boom lasted too long to be mostly explained this way, and involved a big increase in the total number of babies born, not just people getting around to having babies that they’d put off having earlier.

Women squeezed out of the labor force. Increasing employment and educational opportunities for women are one of the long-term drivers of the demographic transition. So were these factors operating in reverse during the Baby Boom? The data clearly rule this out. Women’s wages actually rose rapidly during this period, and older women, with their child-rearing years mostly behind them, responded by entering the labor market in large numbers. In other words, employers were eager to hire women, but young women, at least, thought they had better things to do.

Instead, the best account we have comes from Richard Easterlin. He proposes that the Boom happened because young men encountered an exceptionally favorable labor market, resulting from the conjunction of several factors. (1) Birth rates fell to low levels during the Great Depression, naturally enough. As a result, twenty years on, employers faced a shortage of native-born young men looking for entry level jobs. (2) In the nineteenth century, periods of high demand for labor in the United States saw increases in immigration; levels of immigration tracked the business cycle. But in the mid-twentieth century, legal restrictions made it difficult to increase the supply of labor through immigration. Employers instead had to offer higher wages for entry level workers. Young men felt they were doing well enough – both absolutely and relative to the older generation – to get an early start on marrying, and to support their wives while raising bigger families.


The Baby Boom would be its own undoing however. As the earliest Boomers grew up and started to crowd the job market and the universities, “The Sixties” took off.

Land of samba

1935 -1941

South America largely avoided the all-out international total wars that consumed Eurasia in the twentieth century (although the Chaco war, Paraguay versus Bolivia, 1932-35, was pretty brutal, and civil wars are another matter). But international events made themselves felt even here. Brazil had its own fascist party, the Integralists (founded 1932), with its paramilitary wing, the Green Shirts. However in Brazil, even the fascists couldn’t quite get into the whole National Socialist racial purity thing; the Integralist slogan called for a “Union of all races and peoples.” (“This place would have driven Hitler crazy,” is what one Brazilian told me, talking about race and miscegenation in Brazil.) The Integralists fought the Communists in the mid 1930s, but eventually both sides were suppressed by the dictatorial Estado Novo (New State) in 1937, led by Getúlio Vargas.


In much of the world at the time, liberalism and free trade were out, and nationalism and protectionism were in. In Latin America, this move went under the name of “populism,” favoring urban businessmen and workers at the expense of the old export-oriented land- and mine-owners. This often meant cultural as well as economic nationalism. Brazil today is famous for its Carnival celebrations, including samba parades. Ironically these took much of their current shape during the 1930s, echoing mass rallies in Italy and Germany. The organized samba parades were a means of bringing rowdy public celebrations under official control: from this point on they were officially sponsored, and were expected to march in orderly lines and to celebrate edifying nationalist themes. Early twentieth century samba musicians incorporated a variety of musical styles in their performances; in the 1930s, in the name of “authenticity,” they were encouraged to purge their music of foreign influences, including jazz.

Commerce and coalitions


The theory of comparative advantage is one of the really great theories in the behavioral sciences. It implies that even if country E has an absolute disadvantage at producing every kind of good compared to country P, it can still gain by finding goods for which it has a comparative advantage, and specialize in producing those, and trading for other goods with P.

But the theory of comparative advantage (like another great theory,  the theory of kin selection) needs to be handled with care. Even if a country benefits in the aggregate from international trade, there may be losers as well as winners. As the world came to be increasingly tied together by international trade, conflicts over free trade and protectionism moved to the fore of politics. In nineteenth century England, the free traders, representing industrialists and urban workers, took control, opening the country to cheap imported food. But in the 1870s, both Germany and the United States arrived at political settlements that favored protectionism over free trade.

Germany was unified in 1871. The densely populated country had a comparative advantage in labor and a comparative disadvantage in capital and land. Free trade for Germany would have meant specializing in labor intensive goods, and importing capital intensive goods from more industrialized countries like England, and cheap food from the more thinly populated Americas and Eastern Europe. Instead, Germany put up high tariff barriers to protect her industrialists and landowners – a “marriage of iron and rye.” Germany’s industrial working class was pro-free trade (so was Karl Marx), but their main political vehicle, the Social Democratic Party, was excluded from the government. This political settlement lasted right up to the First World War; on some accounts, the fraying of the protectionist ruling coalition was a factor pushing Germany toward war.

The United States had a different protectionist coalition. In the 1870s the country had an abundance of land, but it was short of labor and still in the early stages of industrialization. Protectionism, supported by Republicans, promoted national industry, and kept high-wage American workers from having to compete with low-wage workers overseas. The agricultural South and West were the big losers under this scheme, but there was a compensating advantage for the South. The compromise of 1876 put the Republican, Hayes, in the White House in exchange for ending Reconstruction in the South. White Southerners then had a free hand to set up a one party state under the Democrats, committed to black disenfranchisement and white rule. When the upstart Populists started winning support in the South and West on a free trade platform, they were beaten back by Southern Democrats playing the race card. The condominium between Republicans and Democrats lasted until the Great Depression of the 1930s

In Latin America at the same time period, the free traders were largely in the ascendant. In Brazil, for example, the ruling coalition stood for café com leite – coffee with milk – São Paulo coffee planters and Minas Gerais cattle ranchers committed to an export oriented economy. Brazil had a lot of vacant land that could be opened up for coffee production, and was able to attract European immigrants to help with the harvest.

In Guatemala by contrast, free trade took a more sinister turn. From 1871, a “liberal” government facilitated the expropriation of Indian lands to promote coffee production, all in the name of progress. Indians were recruited to work on the plantations by a combination of forced labor and debt peonage. The country came to resemble a penal colony under the control of a large standing army.

Joseph Conrad spent his early life as a sailor, and had plenty of chance to see the dark underside of globalization, most famously the Congo rubber trade as depicted in Heart of Darkness. In Nostromo, set in a fictional Latin American republic, he wrote

Liberals! The words one knows so well have a nightmarish meaning in this country. Liberty, democracy, patriotism, government – all of them have a flavor of folly and murder.

The world in 1600

World population, about 545 million

Pangaea reunited. In the century after 1492, West Europeans mastered the winds and currents of the world’s oceans. The shock to the rest of the world would be comparable in some ways to the earlier shock resulting from the spread of nomadism on the Eurasian steppes. In the Americas, the immediate results were devastating, with the loss of most of the population to introduced diseases, helped along by conquest and enslavement. But the spread of new crops and animals in both directions also helped fuel a population boom in the Old World.

Mega-empires. In Eastern Europe and Asia, the results of West European expansion by 1600 were less dramatic. There the landscape was dominated by huge empires: Russia, the Ottomans, Safavid Persia, Mughal India, Ming China. These have sometimes been called “gunpowder empires,” emphasizing the role of cannon in establishing centralized power. But they could also be considered the aftermath of the Mongol conquests, either arising from the overthrow of Mongol rule (Russia, China) or claiming direct Mongol descent (Mughal India). In other words, these empires developed in centrifugal fashion, with power collapsing at the old Mongol center, and new states arising along the Mongol marches.

Charlemagne + 800. Another centrifugal episode of state formation took place in Western and Central Europe, on a smaller scale, over a longer period of time. As the Carolingian Empire disintegrated, new states arose along its marches, in Iberia, in France, England and Scandinavia, and in eastern Germany and neighboring, mostly Slavic territory. Meanwhile the core of the former empire, including western Germany and northern Italy, remained fragmented. By earlier Roman or Asian standards, medieval states in Europe, even when they controlled large areas, were feeble things. The state’s power to collect taxes had more or less collapsed, and Medieval monarchs were forced to concede substantial privileges to their subjects in exchange for their support. By 1600, however, military competition had produced more powerful absolutist states. Medieval liberties survived best in lands where military threats had been less intense, on islands (England and Scotland), on an isolated peninsula (Scandinavia), in the mountains (Switzerland) or soggy lowlands (Holland), or just far from the madding crowd (Poland).

Of cannibals

Three of these men [Tupi Indians from Brazil], ignorant of the price they will pay some day … ignorant of the fact that of this intercourse will come their ruin … poor wretches …were at Rouen, at the time the late King Charles IX was there [in 1562]. The king talked to them for a long time; they were shown our ways, our splendor, the aspect of a fine city. After that someone asked their opinion, and wanted to know what they had found most amazing. They mentioned three things, of which I have forgotten the third, and I am very sorry for it; but I still remember two of them. They said that in the first place they thought it very strange that so many grown men, bearded, strong, and armed, who were around the king (it is likely that they were talking about the Swiss of his guard) should submit to obey a child, and that one of them was not chosen to command instead. Second (they have a way in their language of speaking of men as halves of one another), they had noticed that there were among us men full and gorged with all sorts of good things, and that their other halves were beggars at their doors, emaciated with hunger and poverty; and they thought it strange that these needy halves could endure such an injustice, and did not take the others by the throat, or set fire to their houses.

I had a very long talk with one of them. … When I asked him what profit he gained from his superior position among his people (for he was a captain, and our sailors called him king), he told me that it was to march foremost in war. … Did all his authority expire with the war? He said that this much remained, that when he visited the villages dependent on him, they made paths for him through the underbrush by which he might pass quite comfortably.

All this is not too bad – but what’s the use? They don’t wear breeches.

Of Cannibals. Essays of Montaigne

Brave New World

Columbus’s discoveries overthrew the Medieval conception of Earth’s place in the cosmos. No, he did not discover that the Earth was round. Educated Greeks had known that two millennia earlier. But he also did more than just discover new lands.

The standard, educated medieval view of the cosmos was a synthesis of Aristotle and Christian theology. The universe consisted of larger and larger spheres of more and more rarefied elements: a sphere of earth, a sphere of water, a sphere of air, a sphere of fire (the sublunary sphere, home of meteors), and successive quintessential spheres for the planets, the fixed stars, and heaven beyond. The first two spheres were not concentric, obviously – otherwise the earthly sphere would have been entirely underwater. Instead, Providence had set the earthly sphere sufficiently off-center that some of it – including the whole inhabited world – stuck above the water (Genesis 1:9-10).


Here’s a representation of the old view, still surviving just after Columbus (from David Wooton’s fine recent book The Invention of Science: A New History of the Scientific Revolution). At the very center of the chart, inside the wavy lines representing the sphere of water, is a funny shape: a T-and-O map of the inhabited world. The East, and Asia, are the white area above the horizontal crossbar of the T. The vertical bar of the T is the Mediterranean, with two further horizontal black lines separating Iberian, Italian and Balkan peninsulas to the North (left). Africa is South (right) of the Mediterranean. Not shown on this map, at the very crux of the T, is the holy city of Jerusalem, site of the Crucifixion and Resurrection. T-and-O maps aren’t much use for navigation, but they were popular for a long time because they showed a Higher Truth about the divine order of the Cosmos.

It’s hard to square this conception of the universe with the discovery of a whole New World sticking up on the opposite side of the watery sphere. Columbus tried out various theories. At first he imagined that he had reached the (East) Indies. Later, he started thinking that the earthly “sphere” might have a pear-shaped extension sticking up out of its far side (like a woman’s breast, he put it), rather than being strictly spherical, so you could reach the site of earthly Paradise (the nipple) by sailing up the Orinoco.

The generation following Columbus, beginning with Amerigo Vespucci, abandoned the nested spheres idea, at least as far as earth and water were concerned. When Medieval writers wrote about “the Earth” they generally meant just the earthly sphere, minus the sphere of Ocean. After Columbus, “the Earth” would come to refer to the whole terraqueous globe.


The Waldseeemüller map (1507) is one of the first to show the Old World and the New. Copernicus almost certainly saw a copy of the map. It spurred him to imagine that the Earthly globe – land and water – could revolve around its own axis, and – even more radically – might revolve around the sun.


1508 – 1538

The Spanish Conquistadors, inured though they were to hardship and bloodshed, were nonetheless taken aback by the scale and ferocity of Aztec sacrifice. They wrote horrified accounts of sacrificial rituals, and of tzompantli, the racks where thousands of skulls of sacrificial victims were displayed in front of the twin pyramids of the Templo Mayor.


The Spanish invaders tore down the Templo Mayor and paved over the tzompantli. But archeologists in 2015, excavating under old buildings in Mexico City, uncovered the tzompantli (originally built from 1486-1502) again. Here’s a recent account.

The Aztecs are not the only folk to practice human sacrifice. It’s common, especially in the early stages of setting up chiefdoms and states, where it helps to keep commoners and conquered folk properly terrorized. But the scale of sacrifice on the part of the Aztecs and other Mesoamerican societies is extreme. It’s natural to wonder what in the world was going on, whether there is some deeper reason for the cult of killing, underneath the religious rationale.

Some anthropologists have suggested a materialist explanation. The peoples of the New World had few domesticated animals, a legacy in part of mass extinctions millennia earlier that eliminated a lot of potentially domesticable species. In Mesoamerica, turkeys and dogs were about it. In less densely populated areas, Indians could supplement a diet of domesticated plants with game. But in densely settled Mesoamerica, the main source of animal proteins and fat for the elite was other humans. At least so the story goes. Marvin Harris – kind of a “protein explains all human history!” guy – set out this theory in his popular book Cannibals and Kings.

This is intensely controversial. It’s not clear that eating people on this scale makes much sense from an optimal foraging point of view. But at least we can say that the predatory ethos of Aztec rulers makes a contrast with the more pastoral ethos of many Old World rulers

shepherd king

However there are some comparisons between New World and Old World civilizations where the New World comes off looking better. Gini coefficients* – a measure of inequality – are never going to grab the headlines the way Aztec heart sacrifice does. But the figure below shows something interesting.

new world gini

Figure 3a shows how Gini coefficients change over time in a sample of societies in Eurasia (blue) and North America / Mesoamerica (red), using house size as a measure of wealth. In both cases, the origin of agriculture and the rise of states is associated with increasing inequality. Figure 3b shows the same data, but recalibrated, so that the 0 point on the time scale is set at the origin of agriculture (which happened at different times in different places). The second figure shows a contrast between continents: a further increase in wealth inequality in Eurasia about 5000 years after the origin of agriculture (around 3000 BCE) and on into the Bronze Age, but a steady level of inequality in North America / Mesoamerica. The authors of this study suggest that the greater availability of domesticated animals in Eurasia increased the potential for wealth inequality via “agricultural extensification”, as well as via mounted warrior elites capable of creating (or stimulating the creation of) very large empires.

Result: There is no Templo Major in Eurasia. And there is no Attila or Genghis Khan in North America / Mesoamerica.

calvin and hobbes

* Technical note: Where wealth is distributed perfectly evenly, the Gini coefficient is 0. Where one person owns everything and the other n-1 own nothing, the Gini coefficient is 1 – 1/n.