Monday, July 24, 2017

The 10,000 Year Explosion, Chapter 6: A Summary

Chapter 6 of Gregory Cochran and Henry Harpending’s The 10,000 Year Explosion: How Civilization Accelerated Human Evolution (2009) is called “Expansions,” and examines the genetic effects of large-scale migrations of human beings.

History is filled with examples of certain population groups that conquer, migrate into, or spread over large areas and replace other groups, or replace other groups with some mixing.

Cochran and Harpending (2009: 156) accept that cultural and technological advantages have played a large role in the success of such movements, but also contend that sometimes, in important cases, evolutionary genetic traits have also been a factor. In this respect, as in normal evolutionary theory, we must look at group fitness, and not just individual fitness, as factors in human history (Cochran and Harpending 2009: 158).

Three major examples are analysed in Chapter 6: (1) the success of Europeans in the New World, (2) early European attempts to colonise sub-Saharan Africa, and (3) the astonishing success of the prehistoric Indo-European-speaking peoples.

1. Europeans in the New World
The first example Cochran and Harpending point to was the European colonisation and conquest of the New World.

We know that the Native Americans faced a severe group disadvantage caused by differential evolution: namely, their inability to resist or have immunity to new diseases brought by Europeans like smallpox (Cochran and Harpending 2009: 158–159). The HLA gene alleles, in various forms, protect human beings against infectious disease by regulating the nature and strength of the immune system. But the Amerindians had an unusual distribution of HLA alleles – evolved from their distinct evolutionary history in the Americas – and a much weaker immune system, because they were simply not exposed to the same type and variety of pathogens as the farming peoples of the Old World (Cochran and Harpending 2009: 160–161, citing Cavalli-Sforza and Paolo Menozzi 1994). But the weaker immune systems of Amerindians had an advantage in their distinctive environment: they were much less subject to autoimmune diseases than other peoples with stronger immune systems (Cochran and Harpending 2009: 161).

But when Europeans brought infectious diseases such as measles, smallpox, diphtheria, whooping cough, leprosy, and bubonic plague, the consequences for Amerindians were horrific: there is some evidence that the Amerindian population of the New World suffered a stunning 90% fall in just a few centuries – and most of the deaths were caused by exposure to these diseases introduced by Europeans which Amerindians could not resist because of their different evolutionary history (Cochran and Harpending 2009: 162, citing Cook 1998). For instance, while only about 30% of Europeans might die in smallpox epidemics, a shocking 90% of Amerindians would die from the disease (Cochran and Harpending 2009: 167). This terrible series of plagues obviously aided the European conquest of the Americas, and even with superior European technology, was a factor in the success of the Conquistadors.

For example, the conquest of the Incan Empire by Francisco Pizarro was facilitated by a smallpox epidemic (Cochran and Harpending 2009: 163), as described in this video:



As an aside, it’s curious that this documentary based on Jared Diamond’s Guns, Germs and Steel does not explicitly acknowledge the biological and evolutionary implications of the New World epidemics, because the truly terrible and tragic deaths of millions of Amerindians was the result of different kinds of group genotypes and phenotypes between Amerindians and Europeans, and hence different kinds of group fitness, caused by differential, regional evolution.

As late as the 20th century, isolated populations of Amerindians have suffered the same fate: in instances where first contacts occurred between Amerindians and European-descended people in the 20th century the same European diseases have killed 33–50% of the natives (Cochran and Harpending 2009: 167).

The same kinds of biological differences caused terrible epidemics and mass deaths of Australian Aborigines and Polynesians when Europeans invaded or colonised their homelands as well (Cochran and Harpending 2009: 169).

As Cochran and Harpending (2009: 169) emphasise, anybody who refuses to understand the fundamental role of biological differences between human populations as a factor in European conquest of these regions is in effect denying the reality of Darwinian evolution.

2. Europeans and sub-Saharan Africa
Early attempts to conquer or colonise Africa, even just for trading purposes, encountered a severe difficulty: Europeans discovered that the diseases of Africa had a devastating effect on them. The European people in early expeditions, trading missions and settlements suffered an extremely high death rate from Africa diseases which they had not evolved immunity to (Cochran and Harpending 2009: 171). For example, British soldiers in the Gold Coast died at a rate of 50% (Cochran and Harpending 2009: 171). Right up until the early and mid-19th century, a European conquest of Africa – despite the staggering technological and scientific superiority Europeans had – just wasn’t possible in the way that Europeans conquered the New World. The only major area where colonisation worked was South Africa, and this was because of the temperate climate and the difference in the prevalence of diseases.

Once again, the reason was biological, and was simply the lack of immunity and a different evolutionary history: whereas Africans had evolved their immunity to local diseases and pathogens over thousands of years, Europeans had no such immunity.

It was only with the discovery of drug treatment with quinine in the 1800s that Europeans had a defence against falciparum malaria, and, as scientific medicine began to deal with other tropical diseases, Europeans were able to conquer most of Africa from the 1880s (Cochran and Harpending 2009: 173).

2. The Indo-European Waves of Migration
One of the greatest successes of prehistory was the large-scale Indo-European migrations and conquests in which, over thousands of years, Indo-European people of the Yamnaya culture north of the Black Sea, spread out in all directions (Allentoft et al. 2015: 171; Balter and Gibbons 2015).

There was for many years a scholarly debate about the original homeland of the Indo-Europeans with scholars like Colin Renfrew proposing that the homeland lay in ancient Anatolia (Cochran and Harpending 2009: 178). However, it is now widely accepted that the original Indo-European homeland was in what is now southern Russia above the Black sea (Cochran and Harpending 2009: 179).

For example, from 3,000 to 2,000 BC, there was massive Indo-European migration of people from the South Russian steppe into central Europe, and then into northern and western Europe, and now virtually everybody in Europe speaks an Indo-European language. But modern Iranian and Hindi and Urdu – the major languages of the Indian subcontinent – are also Indo-European. The Indo-Europeans probably had a phenotype with brown eyes, pale skin, and taller height (but interbreeding with other population groups has changed this phenotype, especially in India).

The Indo-European language family was so successful that it now has about 3 billion native speakers, or about 50% of the human race (Cochran and Harpending 2009: 174).

We can see the spread of the Indo-European peoples through the spread of their languages, as illustrated (apart from a few minor mistakes here and there) in the video below:



So why were they so successful?

The Indo-Europeans were not only farmers but also cattle herders, and raised cattle, sheep, goats and pigs, and they may have domesticated the horse (Cochran and Harpending 2009: 176). They seem to have had wheeled carts and chariots, at least in the later stages of history.

But Cochran and Harpending argue that the crucial biological trait that the Indo-Europeans had was lactose tolerance into adulthood, caused by the 13910-T allele, which allows the continued synthesis of lactase (an enzyme that digests milk sugar) past chidlhood (Cochran and Harpending 2009: 180–181; Allentoft et al. 2015: 171). This, they argue, was why the Indo-European peoples were so successful and expanded so many times in thousands of years of history.

At the time, most Europeans (and many other peoples of that time) were lactose intolerant into adulthood:



With their lactose tolerance into adulthood, Indo-Europeans could become highly effective dairying pastoralists, as well as farmers, and could actually produce more high-quality food on a given amount of land than other pastoralists (Cochran and Harpending 2009: 181). In effect, Proto-Indo-European pastoralism had great advantages in inter-group competition, and there was a biological basis to this (Cochran and Harpending 2009: 182).

Indo-Europeans could also abandon farming and become mobile pastoralists, a style of life which has clear military advantages, in contrast to sedentary farmers (Cochran and Harpending 2009: 182). Their dairy-rich diet also gave them greater height, and they soon developed a warlike society (Cochran and Harpending 2009: 183).

So, first of all, Indo-Europeans spread all over the steppe near their homelands, and then into Europe, where they had the edge in inter-group competition and in group fitness against the early European farmers (Cochran and Harpending 2009: 184). Indo-Europeans seem to have conquered or displaced many earlier Europeans, but, perhaps more generally, ruled as an elite and imposed their languages on the native populations (Cochran and Harpending 2009: 184). Interbreeding with Indo-Europeans and gene sweeps then allowed modern Europeans to acquire the trait of lactose tolerance (Allentoft et al. 2015: 171).

Indo-Europeans also spread out eastwards into Central Asia, Iran and even into India.

Underlying this astonishing history of success was the mutation, or mutations, that produced their adult lactose tolerance.

Finally, in the years after 2009 (the year The 10,000 Year Explosion was published), much new genetic evidence has emerged from the revolution in the sequencing of ancient genomes from bones and other remains, which has vindicated Cochran and Harpending’s thesis on the Indo-Europeans:
Andrew Curry, “Archaeology: The Milk Revolution,” Nature, 31 July 2013.

Ann Gibbons, “Nomadic Herders left a Strong Genetic Mark on Europeans and Asians,” Science, 10 June 2015.

Allentoft, Morten E. et al. 2015. “Population Genomics of Bronze Age Eurasia,” Nature 522 (11 June): 167–172.
BIBLIOGRAPHY
Allentoft, Morten E. et al. 2015. “Population Genomics of Bronze Age Eurasia,” Nature 522 (11 June): 167–172.

Balter, Michael and Ann Gibbons. 2015. “Indo-European Languages tied to Herders,” Science 347.6224: 814–815.

Cavalli-Sforza, L. Luca and Alberto Piazza Paolo Menozzi. 1994. The History and Geography of Human Genes. Princeton University Press, Princeton.

Cochran, Gregory and Henry Harpending. 2009. The 10,000 Year Explosion: How Civilization Accelerated Human Evolution. Basic Books, New York.

Cook, Noble David. 1998. Born to Die: Disease and New World Conquest, 1492–1650. Cambridge University Press, Cambridge.

Diamond, Jared M. 2005. Guns, Germs and Steel: The Fates of Human Societies. Vintage, London.

The 10,000 Year Explosion, Chapter 5: A Summary

Chapter 5 of Gregory Cochran and Henry Harpending’s The 10,000 Year Explosion: How Civilization Accelerated Human Evolution (2009) is called “Gene flow,” and looks briefly at the evolutionary changes induced by mixing of genetically distinct populations.

The chapter begins with the concept of a gene allele “sweep,” or the manner in which a favourable gene variant can spread throughout a population of people where interbreeding is general, but not highly isolated and localised. While most gene mutations are harmful or neutral, some are beneficial (Cochran and Harpending 2009: 133). A particular gene can mutate into an allele that then creates a phenotypic trait in a living thing that happens to make that individual more successful and better adapted to its environment. That individual then usually has a selective advantage and survives to have more offspring, and in turn will tend to pass on the favourable allele to more offspring. Over time a small group of individuals with the new trait will survive and be more successful than others who lack it. Over time, a new trait will spread at large in a population and cause evolutionary change.

A gene “sweep” is the process by which a gene variant (an allele) can spread, over time, through a given population. A gene sweep may spread quickly over hundreds of years or, depending on population size and how well-mixed a given population is, over thousands of years. Agricultural populations often practice marriage between neighbouring villages or settlements, and even this local mixing – over enough time – can spread genes and traits over large populations (Cochran and Harpending 2009: 136).

Cochran and Harpending (2009: 137) use a model to suggest that a new allele that provides a selective advantage of 5% will – in a well-mixed population – rise to a high frequency in about 8,000 years.

However, population movements in history have also been a major vehicle by which genetic change and evolution have progressed. While geographical barriers (like oceans, deserts and mountains) and distance have certainly keep many human populations genetically isolated for long periods of time, as in the case of Native Americans and Australian Aborigines, in the Old World of Eurasia gene flow has been much more common.

As a result of trading, colonisation, conquests, the slave trade, and migrations, the Old World has seen a considerably greater degree of gene flow historically as compared with, say, the Americas before the late 15th century or Japan (Cochran and Harpending 2009: 144–145).

It follows, then, that such gene flow – given differential regional evolution – has also been an additional factor in driving genetic change in certain populations.

To take a concrete example, the Roman emperor Marcus Aurelius hired some 8,000 Sarmatians from what is now Southern Russia as mercenaries, and then sent them to Britain, where they appeared to have permanently settled. Cochran and Harpending (2009: 147) speculate that, if these Sarmatians introduced some favourable gene allele variants into Britain, over time many modern British people will now carry those alleles after a few thousand years of mixing. So even a small population movement can, over time, have large genetic effects.

Large-scale population movements and migrations have also been a more radical manner in which gene flow is accelerated. At the end of the Roman empire, there were large-scale migrations of northern Europeans into the Mediterranean world. One such group was the Vandals, who ended up in North Africa. Cochran and Harpending (2009: 151) speculate that the Vandals spread the allele that causes blue eyes into North Africa, so that the blue eyes now found amongst the North African Berbers and Tuaregs can be traced to gene flow between their ancestors and the ancient Vandals.

BIBLIOGRAPHY
Cochran, Gregory and Henry Harpending. 2009. The 10,000 Year Explosion: How Civilization Accelerated Human Evolution. Basic Books, New York.