"Karl Marx was right: socialism works. It is just that he had the wrong species," wrote the sociobiologist, E.O. Wilson, the world's leading authority on ants. But it's really a little more complicated than that, and now is a good time to discuss it, because the 200th anniversary of Marx's birth passed recently. Marx died in London in exile in 1883: so he cannot be blamed for the tens of millions who were killed in his name in the Soviet Union, China and elsewhere in the 20th century. But he did want to change the world, and his goal was equality: the 'classless society'.

Egalitarianism among human beings poses a problem that the cultural anthropologist, Bruce Knauft, dubbed the 'U-shaped curve'. He observed that all non-human primate species are intensely hierarchical - a vertical line - whereas for up to 1,00,000 years before the rise of civilization our hunter-gatherer ancestors were egalitarian - a horizontal line. But as soon as mass civilizations arise, it's back to chimpanzee values. Until quite recently, all civilized societies were steep hierarchies of privilege and power. So draw another vertical line, and you have the U-shaped curve.

This raises two questions: how did human beings break away from the primate norm, and why did they succumb to it again as soon as they became 'civilized'? The best answer to the first question came from another anthropologist, Christopher Boehm, who pointed out that humans were intelligent enough to realize that the usual primate dominance struggle among all the adult males could only have one winner. Since each individual was far more likely to lose than to win, it was in their collective interest to shut the whole dominance game down.

Human beings lived in tiny bands with no hierarchies, not even any formal leaders, for long enough to entrench those egalitarian values in our cultures and maybe in our genes. But even the earliest civilizations had many thousands of people, which disabled all the social control mechanisms that relied on spotting and discouraging the would-be alphas. Moreover, mass societies had complicated economies that needed centralized decision-making. So the alphas took charge, and the millennia of tyranny began. They only ended in the past couple of centuries when democratic revolutions started to overthrow the kings, emperors and dictators. Why now? Probably because the rise of mass media gave the millions back their ability to organize, and to challenge those who ruled over them. They were still egalitarians at heart, so they seized the opportunity; and by now more than half the world's people live in countries that are more or less democratic. But it's only political equality; we never got back the material equality of the hunter-gatherers, and the social hierarchies persist.

Marx's goal was to reconquer the remaining lost ground and create a classless society that lived in absolute equality. It was such an attractive goal that millions sacrificed their lives for it, but it was a pipe-dream. The only way to achieve that kind of equality again in a modern mass society was by strict social controls - and the only people who could enforce those controls were ruthless dictators. So we learned something from the collapse of Communism. Absolute equality comes at too high a price. But too much inequality also exacts a price. People living in modern democratic societies will accept quite a lot of inequality, especially if there is a well-developed welfare State to protect the poor. But if the income differences get too great, the politics gets ugly.

Why did Canadians elect Justin Trudeau as prime minister, while Americans chose Donald Trump as president? The two countries have similar cultures and almost identical per capita incomes, but the richest 20 per cent of Canadians earn 5.5 times as much as the poorest 20 per cent whereas the richest fifth of Americans earn eight times as much as the poorest fifth. Inequality is inevitable, but you have to manage it.