The 10000 year explosion – Gregory Cochran and Henry Harpending. 2012.

cochran

 

Great leap forward some 40,000 to 50,000 years ago: advent of cultural evolution and the end of biological evolution. However modern humans have experience a storm of change over the past 50,000 years.

It is clear that natural selection can proceed quite rapidly  (e.g. domestication of dogs in less than 15,000 years, of plants (corn) in 7000 years) and that the past consist of long periods of near-stasis interspersed with occasional periods of very rapid change.

The Ice Age ended some 11,500 years ago.

The conclusion that all humans are effectively the same is unwarranted. Evolution has taken a different course of different populations. Over time, differences among populations have accumulated.

We expect that differences between human ethnic groups are qualitatively similar to those between dog breeds (shallow).However differences between dogs are not so small. Very significant evolutionary changes in response to agriculture were still possible.

Someone from Nigeria may have sickle-cell mutation (a known defense against malaria) while hardly anyone from northern Europe does, but even the majority of Nigerians who don’t carry sickle cell are far more resistant to malaria than any Swede. They have malaria-defense version of many genes.

In principle, differences in a single gene could cause significant trait differences between human populations.

We believe that obvious differences between racial groups are linked to gene variants that have recently increased in frequency and had major fitness effect.

We are signicantly different from our ancestors 40,000 years ago and different from our ancestors of early historical times. We can empathize with the heroes of Iliad but we are not the same.

In most humans – and in mammals generally – lactase production stops around the age of weaning, but in Europeans and some other peoples, production continues throughout life. This adaptation lets adults drink milk. Lactose-tolerant Europeans carry a particular mutation that is only a few thousand years old.

Since we have sequenced the chimpanzee genome, we know the size of the genetic difference between chimps and humans. Since we have a decent estimates of the length of time since the two species split, we know the long term rate of genetic change. The rate of change over the last few thousands years is far greater that this long term rate (100 times greater).

The ultimate cause of this accelerated evolution was the set of genetic changes that led to an increase ability to innovate.

P 25 Moderns showed up in Europe about 40,000 years ago. A superior tool kit – in particular needles for sewing clothes – may have made permanent settlement possible.

Modern human had projectile weapons, as opposed to Neanderthals. Another hypothesis is that modern humans had developed advance language capabilities. Moderns had long distance trade (favoured by language abilities probably) probably favoured formation of large scale alliances. Modern humans carried some disease and parasite that was fairly harmless to them but deadly to Neanderthals.

In southwestern France, we find tool tradition  from 35,000 to 28,000 (Chatelperronian) that appear to combine some techniques of the Neanderthals (Mousterian) and the moderns (Aurignacian). This tells us that there were interactions between both, Neanderthals can’t have been all that far behind modern human in terms of cognitive capabilities. (Archaeological artefacts from as recently as 100,000 years ago do not show real differences between both culture)

With the advent of modern humans in Europe, innovation was bustin’ out all over.

Spearpoints and scrapers of this period often used materials from hundreds of miles away. Bones and ivory are used as well. They had a more varied diet (and perhaps safer hunting methods) and new methods of preserving food. They used the fire better, made lamps and pottery figures. They built much more substantial protective structures.  They invented art. We have clear cut evidence of burial rituals. But being modern was not enough to trigger so much innovation. We don’t see this storm of innovation in Australia. So something important, some genetic change, allowed moderns to expand out of Africa and supplant archaic sapiens.

Human did not invent agriculture anywhere on earth during the Eemian period (interglacial period of about 125,000 years ago). They did so a least 7 times independently in the  Holocene, the most recent interglacial which began 10,000 years ago.

Genetic changes allowed important human development in 40,000 BC that were not possible 100,000BC : the human revolution. Some mechanism must have been at play that could cause unusually rapid genetic change. That mechanism, we believe, was introgression – that is, the transfer of Alleles from another species, in this case Neandertals.(case of introgression includes most domesticated plants and e.g. cows: taurine in the middle east and zebu in india are interfertile although they were separated several hundred thousand years ago.)There is no faster way of acquiring new and useful genes. The key point: rare interbreeding can be very important, as it introduce new gene variant in the population. So much so that even a few dozen half Neanderthal babies over thousands of years would have allowed modern human to acquire most of the Neanderthals’ genetic strengths.

 

The two specied had separated fairly recently, roughly half a million years earlier.

Venus of Dolmi Vestonice – 27,000 BC

Venus of Willendorf  23,000 BC

Lion Man of Hohlenstein, 30,000 BC

Some have seen evidence of Neanderthal features in some of the earliest form of moderns in Europe. Other dispute the matter.

Haldane : if the allele confers an advantage s, its chances of going all the way in 2s. IN a stable population, a single copy of an allele with a 10% fitness advantage has a 20% chance of eventually becoming universal.

Home heidelbergensis , the common ancestor of Neanderthals and moderns, settled both Europe and Africa about ½ million years ago. Both developed a larger brain.

Adaptation depends on supply of favourable mutations, which are generated randomly, thus two populations facing the same problem may well find different solutions and those solutions need not be equally efficient. (e.g. Amerindians from high andes have plenty of red cells, Tibetans have lower levels of haemoglobin but breathe faster to take more oxygen. They are both better adapted than flatlanders, and Tibetan solution is more efficient than its Andean equivalent).

Over a few centuries, people in areas where camel were available abandoned wheeled vehicles and roads almost entirely: the motto here is that sometimes the apparently inferior choice has better upgrade path.The seemingly inferior choice may come out on top down the road:excess heat production limited the trend toward larger brains in Africa, while in Europe heat was not much of a problem. Later, as evolution fine-tuned the physiology of large brains, much of the heat problem was solved and so the new brain could then spread in Africa as well.

5% of genetic variation among both Europeans and Sub-Saharan Africans originated in archaic humans such as the Neanderthals. (there may have been archaic population in Africa as well (with variants only found in Pygmies for instance).

Microcephalin (MCPH1) is a gene that regulates brain size. Most people today carry the same version of it indicating a recent origin, estimated at 37,000. Neanderthals are a reasonable, indeed likely, source. FOXP2, who plays a role in speech was replaced by a new variant some 42,000 years ago (and existed among Neanderthals). It is surprising that we may have acquire our speech capabilities from Neanderthals, but not impossible.

There was 2 streams out of Africa 50,000 years ago – one to Europe and Central Asia, one to the far east to Australia and New Guinea. There is no trace of creative explosion in the second streams. Populations there brought and retained Neanderthal grade technology and culture.

P64. By 40,000 years ago, humans had become both anatomically and behaviourally modern (but exactly like people today). They had vastly greater powers of innovation than their ancestors, likely owing in parts to genes stolen from their Neanderthals cousins.

60,000 year ago there were 250,000 modern humans. By the bronze age, 3000 years ago, that number was roughly 60 million. 100,000 years ago there was half a million people (moderns+archaic (Neanderthals + erectus). Some 12,000 years ago, there were 6 millions modern humans. From 10,000 BC to AD1, world population increased hundredfold.

 

Farming produces 10 to 100 times more calories per acre than foraging. Shelter, artefacts no longer had to be portable. Births could be spaced closer together since mother did not have to continually carry small children. For the first time, humans could begin to accumulate wealth. Governments come up, limiting local violence (allowing government to extract resources from their subject).

New mutations have played a major role in evolutionary agriculture and there was a vast increase in the supply of those mutations just around this time because of population increase associated with agriculture. More mutation occurred in large populations, some of them beneficial. By 5000 BC, new adaptative mutations were coming into existence at a tremendous rate, roughly 100 times more rapidly than in the Pleistocene.

There is every reason to believe that early farmers developed serious health problems from this low-protein, vitamin short, high carbohydrate diet (infant mortality increased due to poor diet) Humans who adopted agriculture shrank (average height dropped by five inches).

Over millennia population responded to these new pressure: people with genetic variants that helped them deal with the new diet had more surviving children.

Hunter gatherers and mammals stop making lactase in childhood. But after the domestication of cattle, milk was available to people of all ages. A mutation that caused continued production of lactase originated 8000 years ago and spread among Europeans. Similar mutations occurred  in Tutsi populations.

Vitamin D shortages may have driven the evolution of light skin in Europe and northern asia. Since there is plenty of vitamin D in fresh meat, hunter gatherers in Europe may not have suffered from Vit D shortages and may have fairly dark skin. Several mutations causing light skin colors originated after the birth of agriculture.

P 80 . population that have never farmed/not formed for long, such as the Australian Aborigenes and many amerindiens have health problems when exposed to western diets: high incidence of diabetes of type 2. Prevalence of diabetes in Aborigenes is 4 time more than in other Australians: we think this is a consequence of a lesser degree of adaptation to high carbohydrate diets. Polynesians are more prone to diabete (3 times the European rates) despite some agriculture (yams; taro, bananas etc.°): adaptation has been incomplete due to the relative small size of population and low rate of protective mutations. Limited contacts with far flung Polynesian islands would have interfered with the spread of any favourable mutations.

One hypothesis is that Pre agri population were prone to famine and developed metabolic differences that helped people to survive food shortages als led to diabetes in modern environments. Authors argue that hunter gatherers were less prone to famine as violence would keep their population low. In addition they seem not to have division between well fed elites and hungry lower classes (as opposed to agri society). A response based on adaptation to carbohydrate seems better.

P87 Malaria: people have developed genetic defences against it, and the side effects of those defences account for most cases of genetic diseases in populations originating in those regions.

Most important mutations to protect against malaria are those that change features in the red cells  which are the primary target of malaria parasite (sickle cells etc.).  This can lead to anemia, Duchene muscular dystrophy etc. These defences became common because they gave an advantage to carriers. However they cause problems in people with 2 copies. This is unusual (for instance an allele that makes carriers run faster does not cripple people with two copies) and probably because malaria (and adaptation to) has not been around for very long (perhaps 4000 years). The main African version is 2500 year old.

The sets of changes driving light skin color in China are almost entirely different from those performing the same function in Europe. SLC24A5 seems to be variant with most impact on skin color in Europeans came into existence abut 5,800 years ago. It spread very fast – so must have brought huge selective advantages. It may explain why Romans had the impression that scotts were dark skinned. This may have been driven by an increased need for vitamin D. If correct, why would that be different in Asia? And why lot’s of variety of Europeans (read heads and blondes, blue eyes and green eyes. Nowhere else in the world is that sort of variety.

A number of new, rapidly spreading allele have to do with central nervous system. Several affect serotonin, a neurotransmitter involved in regulation of mood and emotion.

We have reason to think that humans circa 100,000 had stronger muscles than today – and so changes in dystrophin complex may have sacrificed muscle strength for higher intelligence.

Genghis Khan as exemple of elite reproductive advantage. Today 16M men in central asia are is direct male descendant.

If a high fertility subpopulation was reproductively isolated for long enough,selective pressures specific to that social niche might cause them to evolve in an unusual direction and become significantly different from the surrounding population : Ashkenazi jews (strong prohibition of intermarriage and an odd social niche in wich certain traits conferred high fertility.)

P111 Since the elites were in real sense raising peasants just as peasants raised cows, there must have been a tendancy for them to cull individuals who were more aggressive than average, which over time would have changed the frequencies of those alleles that induced aggressiveness. The 7R allele, associated to hyperactivity disorder is associated to this and is totally absent from East Asia (Chinese/Japanese population may have been tamed more than others).

If strong government made possible by agriculture essentially tamed people, people with nonexistent agricultural experience should be less submissive, on average. Bushman from south Africa has been described as the anarchist of south Africa. It was said of Indians with no exposure to agriculture that they could not be enslaved (by puritans in America).

Farming requires certain personality traits (patience, self control, ability to look for long term benefits instead of short term satisfaction) and natural selection must have gradually made such personality more common.

Agriculture has led to the birth of property. Ant-like behaviour must have increased in frequency, selfish, hardworking, self-denying people were far more common than they had been among hunter gatherers.

Groups that became agriculturalist recently – or not at all – are slow to master important social and technical development. This is the case of Amerindians in south America. The well know middlemen minorities (Armenians, jews, Lebanese, parsees, Indians and Chinese) all descended from long established agricultural populations.

Gradual biological changes played a key role in the birth of the industrial and scientific revolutions. Economist have shown that the age of transition to agriculture appears to have a strong influence on a country’s economic development.

Phase transition: modest biological changes might also trigger dramatic social changes by crossing some threshold, just as tiny increase of temperature can turn ice into water.

The scientific revolution may well have resulted from modest changes in gen frequencies affecting key psychological traits. But we believe that there was no selection favouring creativity itself and that creative individuals are accidental by product of other traits, traits that paid off in everyday life (such as ability to make complex model). Creativity seldom confers large fitness advantages, because new ideas can be rapidly copied by others.

Blue eyes is a due to a new allele of the gene OCA2. This allele accounts for 75% of the variation of eye color in Europe. It originated some 6-10,000 years ago in northern Europe (Lithuania). Vandals (in Mauritania), Romans, Greeks spread the genes across the world (Central Asia, north Africa…)

There is every reason to believe that the ancestor of all languages was once spoken by a particular people living on some particular region. One idea is that Indo European languages were carried along by an expansion of early farmers from Anatolia around 7000 BC. Uralic language appear to have had extensive contact with indo-european and they may share a common ancestry . Since finnish people lived in the Russian forest, Anatolia was probably not the place of origin.

Second hypothesis: Kuran model, Kurgan from Pontic –Caspian Steps as  the proto-Indo Europeans. We suggest the advantage driving those indo European expansions was bilological – a high frequency of the European lactose tolerance mutation (13910T allele). Adult population could drink milk, allowing a new pastoralism to be possible: dairy products means more calories, more high quality food. More warriors could be fed on the same piece of land. Cattle was made more important, valuable and was subject to theft more easily than a heap of grain. Fighting for cattle, planning revenge and raids led to the development of warrior societies. This has happened at least three times (in east Africa (upper nile) and Arabian peninsula)  due to lactose tolerance mutations of their own.

Ashkenazi jews have the highest IQ of any ethnic group known. They average 112-115, well above European norm of 100. They also have an unusual set of serious genetic diseases. We propose that they have a genetic  advantage in intelligence that arose from natural selection for success in white-collar occupations during their sojourn in northern Europe.Strong selection for intelligence also produce some unpleasant side effects. IQ test predict academic achievement and other life outcomes, and IQ score are highly heritable . IQ test are imperfect but a useful measure of intelligence. Ashkenazi jews have won more than a quarter of all Nobel science prizes and account for half of the 20th century world chess champions, although they make less than 1/600 of the world population.

Azhkenazim increasingly specialised in one occupation, finance, left open to them because of the Christian prohibition of usury. The majority of Ashkenazim seem to have been moneylender by 1100 and this pattern continued for several century.They had managerial and financial jobs, jobs of high complexity, from 800 to 1700. 90% of the population had to farm to produce enough to feed themselves and productivity was too low to feed a large crust of rulers, scribes, merchants, soldiers etc. Scribes and merchants could somehow become an ethnic group, one defined by occupation rather than location. This did not happen in the Muslim world so strongly. Greek Christians and Armenians competed with Jews in the financial sector. There was less persecution. There was many more jews than in Europe and less white collar jobs: so more tended to have ‘dirty’ jobs. Non Ashkenazi jews do not have high average IQ scores.

Jews as a whole are not a single genetically distinct group, however, some subgroups are-in particular the Ashkenazim. An endogamous group can remain genetically distinct, or become genetically different from neighboring people, if that social pattern persist. Ashkenzim were endogamous for a long time, rarely marrying outside their faith. This was combine with external prejudice.  Prosperous individuals have more children (natural selection), Ashkenazi jobs were cognitively demanding, intelligence is highly heritable.

IQ is partially determined by genetic factors. Siblings with the same biological parents have similar IQs. IQ in childhood is more susceptible to environmental influence. Surprisingly, the way in which a family raises children seems to have no effect on adult IQ.