Nicholas Wade

The genome of history

DNA explains more than you think

The genome of history
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[/audioplayer]Ever since Darwin published his uncomforting theory, people have been trying to exempt themselves from one or another of its unwelcome consequences. Today’s equivalents of the 19th century’s outraged clerics include the many social scientists, economists and historians who insist that evolution is of no relevance to their disciplines.

In the United States the leading social science organisations proclaim that race is a social, not a biological construct. They reject the obvious notion that races differ because the populations on each continent have been evolving independently of one another for the last 50,000 years. Economists treat people as interchangeable entities of little or no intrinsic interest. Could the nature of the humble human units that produce and consume all of an economy’s goods and services have any bearing on a society’s productivity? Heavens, no! That wouldn’t compute at all. Historians, too, like other social scientists, assume that social groups differ only in their culture, not their genetics, and dismiss the idea that inherited social behaviour might make Chinese society, say, slightly different from that of a hunter-gatherer band.

All these academic tribes have been averting their eyes and minds from the discoveries flowing out of the human genome during the past decade. These show that human evolution has been extensive, recent and regional.

Fingerprints of natural selection

Scientists scanning the genome for evidence of natural selection have detected signals of many genes that have been favoured by natural selection in the recent evolutionary past. No less than 14 per cent of the human genome, according to one estimate, has changed under this recent evolutionary pressure. Most of these signals of natural selection date from 30,000 to 5,000 years ago, just an eye-blink in evolution’s three-billion-year timescale. Recent evolution is very hard to detect, but with suitable groups, such as the large patient populations studied for medical reasons, one can see natural selection at work at the present day. Under the pressure of selection, the age of first reproduction among women born between 1799 and 1940 on L’Isle-aux-Coudres, an island in the Saint Lawrence River near Quebec, fell from 26 to 22 years. The researchers who gleaned this finding from the island’s parish records noted that the tendency to give birth at a younger age appeared to be heritable, confirming that a genetic change had taken place. ‘Our study supports the idea that humans are still evolving,’ they write. ‘It also demonstrates that microevolution is detectable over just a few generations in a long-lived species.’

Evolution doesn’t stop. Humans are no exception to the rule, and there’s no reason to suppose human evolution ground to a halt at some decent interval before the present, as historians and economists habitually assume.

The other fact to emerge from the genome is that natural selection has been regional. In the genomes of the three main races — Africans, East Asians and Caucasians (i.e. West Eurasians, meaning Europeans, Middle Easterners and people of the Indian subcontinent) — different sets of genes bear the signatures of natural selection. This is an interesting finding, but hardly surprising: each race, evolving independently, has adapted to its own set of regional challenges.

Yet many social scientists profess to believe that there is no biological basis to race. ‘Race is a recent human invention,’ proclaims the American Association of Anthropologists. ‘Race is about culture, not biology.’ Scientists who have been indoctrinated in this view find it hard to accept any other. Researchers get attached to the view of their field they grew up with, and, as they grow older, they may gain the influence to thwart change. For 50 years after it was first proposed, leading geophysicists strenuously resisted the idea that the continents have drifted across the face of the globe. ‘Knowledge advances funeral by funeral,’ the economist Paul Samuelson once observed.

Academics, obsessed with intelligence, fear the discovery of some gene that will prove one group of people to be brighter than another. In fact intelligence is probably governed by hundreds of genes, each with so small effect that none has yet been detected. But even if it were proved that one major race was genetically more intelligent than another, what consequence would follow? In fact, not much. East Asians score around 105 on intelligence tests, an average above that of Europeans, whose score is 100. A higher IQ score doesn’t make East Asians morally superior to other races. East Asian societies have many virtues but are not necessarily more successful than European societies in meeting their members’ needs.

Indeed, it’s hard to see anything in the human genome that would support any notion of racism. The genome proclaims the unity of humankind. Not only do all humans carry the same set of genes, but races are not even demarcated by alleles, the alternative forms of a gene. In fact they are not demarcated at all, in the sense of having any definable boundary; races differ merely in relative allele frequencies. It’s because of characteristic differences in allele frequencies, however, that geneticists can track along the genome of someone of mixed race, such as an African American, and assign each segment to an African or European ancestor. This exercise would be impossible if races lacked an evolutionary basis.

Natural selection and social behaviour

The genes that bear the fingerprints of natural selection affect nutritional metabolism, bone structure, skin colour and some are also active in the brain. Their role is unknown, but evidently brain genes are as much subject to natural selection as any other category of gene. A class of brain gene particularly likely to fall under evolutionary pressure is that of genes that affect social behaviour.

Edward O. Wilson was pilloried for suggesting in his 1975 book Sociobiology that many human social behaviours might have an evolutionary basis; his Marxist critics wanted to keep the mind a blank slate, mouldable by governments into Socialist Man. Research since then has established that Wilson was correct. From their earliest years, children wish to be part of a group, to obey its rules and to punish violators. People have an instinctive morality, a readiness to make any sacrifice in defence of their family or group. These and several other social behaviours seem to be inherent and therefore genetically based, even though the relevant genes have yet to be identified.

Any trait that has a genetic basis can be modified by evolution. There are reasons to think that social behaviour would be vigorously shaped by natural selection. One is that people survive not as individuals but as social groups; the nature of a society is highly relevant to its success and therefore likely to be a target of selection. Social species are rare and very difficult for evolution to contrive, but once the necessary altruistic instincts are in place, social species are highly successful. Both ants and humans have conquered the world, though fortunately at different scales.

In the case of ants, nature’s strategy been to keep the ant body much the same but to vary its social behaviour. Slight tweaks in social behaviour can quickly adapt an ant society to a different ecological niche. Thus leaf-cutter ants cultivate a mushroom-like fungus in underground caverns, army ants conduct devastating raids, other ants live in the thorns of acacia trees and so forth. Evolution has developed some 15,000 ant species just by varying their social behaviour.

With people, evolution seems to have followed the same strategy: keep the human body as is, but vary the social behaviour to let people exploit new niches. Humans are still a single species, but at least three evolutionary changes in social structure seem evident.

Historical changes in social structure

One is the transition from foraging to settled life. Modern humans first appear in the fossil record some 200,000 years ago, yet the first settlements date to merely 15,000 years ago, in the Near East. Putting a roof over one’s head and being able to own more than one could carry on one’s back seems such an obvious step. So why did it take 185,000 years for people to figure it out? Probably because it wasn’t a matter of perceiving the benefits of settled life, but of evolving the necessary social behaviours. Hunter-gathers are aggressive and egalitarian. Settlers live in larger groups and have to get on with people they are not related to. They must accept hierarchy and division of labour. The reason these behaviours appeared so recently is because they took so long to evolve.

Another social transformation that is evidently hard to make, and probably requires a makeover of social behaviour, is the transition from tribalism to modern states. Tribalism is the default human social organisation. It can be extremely effective — the world’s largest land empire, that of the Mongols, was a tribal state. It is also hard to abandon, so hard that an evolutionary shift in behaviour seems required. China was the first state to replace tribalism, developing in its place a bureaucracy beholden to an autocratic leader. Population build-up between the Yellow and the Yangtze rivers and incessant warfare between tribes were the forces under which the tribal system collapsed. The unification of China in 221 BC marked the emergence of the first modern state. Europeans took another thousand years to escape tribalism, noted symbolically as the time when the King of the Franks became King of France. Other populations, particularly in the Middle East and Africa, are in the throes of achieving this transition.

More specific evidence that evolution has shaped human social behaviour in the recent past comes from a third major social transition, from agrarian to modern economies.

This transition is usually known as the Industrial Revolution. Before the Industrial Revolution, almost everyone in agrarian economies but the rich lived near the edge of starvation. Whenever any improvement in farming technology raised productivity, more children were born, the extra mouths ate up the surplus and semi-starvation soon reigned again. This harsh regime is known as a Malthusian economy after the Revd Thomas Malthus, who described it in his 1798 ‘Essay on the Principle of Population’. As it happened, the Malthusian regime was nearing an end at the very time Malthus was writing because of the vast increase in productivity that was the essence of the Industrial Revolution.

The cause of the Industrial Revolution is the central issue of economic history, yet economic historians have arrived at no consensus as to what that cause or causes may have been. Their preferred candidates are institutions of various kinds, or access to resources. For a quite different explanation, step back to Malthus for a moment. It was from Malthus that Darwin derived the idea of natural selection. Darwin perceived that if people were struggling on the edge of existence, as Malthus described, then a person with the slightest advantage would have more children and bequeath this advantage to them. ‘Here then I had at last got a theory by which to work,’ Darwin wrote in his autobiography.

If the English population provided the example from which Darwin intuited the idea of natural selection, that population was surely being subjected to the same force. The question then is what traits were being selected for. The economic historian Gregory Clark, of the University of California, Davis, has documented four behavioural changes in the English population between 1200 and 1800 AD.  The level of violence declined, literacy increased, and so did work hours and the propensity to save. The effect of these changes, Clark notes in his 2009 book Farewell to Alms, was to transform the violent peasant population of 1200 into the disciplined workforce of 1800. Because the nature of the people had changed, productivity soared, and for the first time an increase in population failed to drag down the standard of living.

Clark not only documents the behavioural change in English society but also provides a plausible mechanism of hereditary transmission. From the study of wills he finds that the well-off had more surviving children than the poor. Since the size of the English population remained fairly constant, many children of the rich must have dropped in social status, diffusing the genes and values that had made their parents wealthy into the wider -population.

The same process presumably occurred in other agrarian populations, which is why the Industrial Revolution spread so easily to other European countries and later, after political obstacles had been removed, to the countries of East Asia.

With all three transitions, an evolutionary change is plausible but remains a hypothesis nonetheless: proof awaits discovery of the relevant genes.

Human differences

The continental populations or races have evolved largely independently ever since modern humans spread across the globe from their African homeland some 50,000 years ago. In many respects their evolution has been largely in parallel. Thus both Caucasians and East Asians have developed the pale skin necessary for living in high northern latitudes, but each has a different set of alleles for doing so. This is not so surprising: evolution can only work with the mutations available, and different mutations for contriving pale skin were present in the Caucasian and East Asian populations.

In social behaviour, too, the three main races have followed largely parallel tracks but on slightly different timescales, probably because of demographic factors. Caucasians first made the transition from foraging to settled life, East Asians were the first to abandon tribalism. In adapting to their local environments, these societies naturally gained different skills and attributes. For most of recorded history, Chinese civilisation has been more advanced than others. Since 1500, the societies of the West have shown greater dynamism and creativity. Clearly no society is intrinsically superior to any other, but inevitably each has its periods of greater relative success.

Many important features of today’s world lack explanation. Why are some countries rich and others persistently poor? Capital and information flow fairly freely, so what is it that prevents poor countries from taking out a loan, copying every Scandinavian institution, and becoming as rich and peaceful as Denmark? Africa has absorbed billions of dollars in aid over the past half-century and yet, until a recent spurt of growth, its standard of living has stagnated for decades. South Korea and Taiwan, on the other hand, almost as poor at the start of the period, have enjoyed an economic resurgence. Why have these countries been able to modernise so rapidly while others have found it much harder?

The answers to such questions may lie in a hitherto unexamined possibility, that human social nature has been shaped by evolution and that human groups therefore differ slightly in their social behaviour and in the social institutions that depend on that behaviour. This would explain why it is so difficult to export American institutions into tribal societies like those of Iraq or Afghanistan, just as it would be impossible to import tribal systems into the United States or Europe. Persistently poor countries, particularly those that are still tribally organised, have not been through the Malthusian wringer experienced by agrarian populations and may therefore find the transition to a modern state that much harder.

People, unlike institutions, can easily migrate from one society to another. Recall evolution’s formula for social species: keep the organisms the same, just transform the social behaviour. Human nature is pretty much universal apart from slight differences in social behaviour, variations in which can lead to very different kinds of society. Significant human differences lie at this level, not that of individuals.

If the fear of racism can be overcome sufficiently for researchers to accept that human evolution has been recent, copious, and regional, a number of critical issues in history and economics may be laid open for exploration. Race may be a troublesome inheritance, but it is better to explore and understand its bearing on human nature and history than to pretend for reasons of political convenience that it has no evolutionary basis.

Nicholas Wade has worked at Nature and Science magazines and is a former science editor of the New York Times. A Troublesome Inheritance by Nicholas Wade is published by Penguin.