Envision a world map. Try to think of where the wealthy countries are. North America and Europe are the first to come to mind. The Pacific Rim and Australia clearly make the list as well. Now think about where all these wealthy regions lie. Every one is to be found toward the top or very bottom, in the temperate zone, well away from the tropics.

This is a world climate map, but if you looked for one of GDP it would be strikingly similar

The delineation is striking. In fact, there is a single line of latitude that divides the world into rich and poor, developed and undeveloped, skyscrapers and slums. The thirty-third parallel north runs below Los Angeles, along the southern coast of the Mediterranean, through southern Iran, and down the Yangtze River valley. In the south, it cuts off just above Buenos Aires, Cape Town, and Sydney. Outside this zone lie all the wealthy regions of the world. Between the parallels lie only four nations classified as Very High on the Human Development Index: Singapore, Hong Kong, Qatar, and the United Arab Emirates, all tiny city-states founded by cold countries and entirely dependent on financial services or oil exports to them. The rest of the warm world is a patchwork of banana republics, failed states, and squalid slums.

The concentration of wealth and power in cooler regions is as old as human civilisation, and has grown stronger over time. Mesopotamia and Egypt were the warm incubators of early civilisation. Up until the early modern era, when economies were rural and the wealth of nations depended mostly on agricultural productivity, India and southern China were considered fabulously rich (though the great majority of people lived in the same squalor as their peers in Dark Ages Europe). But though the breadbaskets of the Roman Empire and imperial China enjoyed virtually year-round warmth, their nerve centers were cooler. By the age of imperialism, white men in wintry cities reaped lucrative profits as their sable subjects toiled under the scorching equatorial sun. In recent decades, the boom of regions like Southern California and Western Australia was possible only with the advent of air conditioning. Our advancing civilisation has climbed ever northward, until the point at which we are able to make the all the world feel like home.

The ancient distinction has caught the attention of men from Aristotle to Cecil Rhodes. Baron de Montesquieu observed that chilly climates and tough living conditions made men “industrious, sober, inured to hardship, courageous, and fit for war,” while mild winters and rich harvests led to “ease, effeminacy, and a certain fondness for the preservation of life.” A visit to Muscovy might have given Montesquieu second thoughts on the sobriety of northerners, but the natural selection gradient is as present today as in the eighteenth century. If you live in a flimsy shack made out of sheet metal in a place where it snows, you will freeze. If you are in a place where there are palm trees, you can have a dozen children who will likely be doomed to the same fate as you.

These Brazilians would not last long in a blizzard

On a quotidian level, cold and heat certainly do engender different levels of activity. On a cold day, the heart and body must work harder just to stay warm, while on a warm one, lethargy conserves energy. During a blizzard one has to move about. Even lounging by the fire presupposes a well-insulated, adequately-supplied house. In the tropics you just lounge on the beach or take a day-long siesta. Spain, southern Italy, and Latin America are well-known for their vibrant nightlife, but it comes at the expense of sleeping off the previous night through the most productive working hours of the day.

In ancient times, the vast natural wealth and fertile soil of India gave its rulers no reason to come up with any better way to do things. Meanwhile, Europeans faced with frigid winters and unreliable harvests were forced to get creative. Northern Europe was doomed to be a poor backwater as long as agriculture was king. When commerce and industry revolutionized the economies of nations like Britain, France, and Germany, things changed.

Technology and general advancement increase exponentially. A relatively small edge in climate for northern over southern Italy led, over the centuries, to vastly different economies and societies. In the chilly, hilly north, wealthy, independent city-states grew and thrived, eventually unifying the nation and driving its modern economy. Meanwhile southerners, contented with friendly weather and hearty harvests, lived under foreign domination in a backward society, with a work ethic that continues to lag hopelessly behind their northern countrymen. Florence is not exactly cold, but she and her neighbors fostered the Renaissance while Naples stagnated.

Neither is this phenomenon a function of European exceptionalism. Southern China was historically the economic powerhouse of the country, but even at the risk of Mongol attack the capital was almost always in the north. Temperate Japan was the first Asian nation to industrialise, and it is now joined by South Korea and Taiwan (whose hub is in the northernmost temperate tip of the island) as one of the wealthiest nations in the world.

There is a weaker, but still interesting correlation between climate and culture. Southerners tend to be hospitable and friendly, though are often stereotyped as hotheads. Leaders from Louis XIV to antebellum U.S. presidents struggled to get their southern subjects to stop dueling. Northerners, more defined by an urban or a self-sufficient ethos, are industrious but usually not too friendly. Warmer regions of countries, such as Queensland in Australia or the American South also tend to be more politically conservative. This is more complicated on an international scale, but it is true that all countries that still execute witches lie in the tropics. The determinism is not as powerful as it is for the economy or broader civilisation, but surely stems from the same causes.

Another prime example of the ancient divide, which opened a chasm in the industrial age, can be seen in the disparate development of the northern and southern regions of the United States. During the war for independence, British regulars in Massachusetts resented the industry, tenacity, and general nastiness of their foes, and longed for the hospitality of honourable Southern Loyalists. As the decades wore on, Northern cities industrialised and railroads criss-crossed the country. Meanwhile, the South clung to slavery and most white men remained subsistence farmers. When the cotton barons declared independence, the South was ground into dust under the Yankees’ iron boot. The Southern states continue to lag behind to this day.

Of course, climate determinism only goes so far. Many of the world’s coldest places, far from clear roads and thawed ports, are still virtually unlivable. Most of Russia remains backward, while Iceland thrives. But before leaping to counterexamples of wealthy warm places, we must remember whence the people who now live in Australia and the American Sun Belt came. Also, though there are certainly many clever Indians and wealthy Brazilians, remind yourself how the vast majority of their countrymen live back home. Surprisingly, migration of colonists from Europe confused the geography relatively little, because they either recreated European society on new soil (in temperate places), or became the thin layer of cream at the top of countries populated mostly by poor natives or imported slaves.

As colder nations gained and pressed their advantage, they also developed and spread technologies that enable man to conquer nature. Commerce, colonisation, and air conditioning have spread the achievements and culture of chilly Europe across the world. On the other hand, the advancement has only pushed the epicentre of civilisation inexorably further north, sharpening the cold edge. Four thousand hectic years have acted as a whetstone, so it is hard to imagine the coming centuries will blunt it.

With that, merry Christmas. I hope yours is a white one.

Former linguistics student; current investment bank analyst who sometimes thinks about something other than spreadsheets