Friday, July 21, 2017

The 10,000 Year Explosion, Chapter 2: A Summary

Chapter 2 of Gregory Cochran and Henry Harpending’s The 10,000 Year Explosion: How Civilization Accelerated Human Evolution (2009) is called “The Neanderthal Within,” and examines the possibility that early humans outside of Africa interbred with Neanderthals, and how this affected human evolution.

Neanderthals and early Homo sapiens outside of Africa encountered one another and competed for resources – and early humans won out in about 10,000 years, perhaps because:
(1) our ancestors had projectile weapons (e.g., throwing spears, darts, bows and arrows) which they could use much more effectively with lighter, less bulky bodies (and so they required less calories to live);

(2) early humans were more intelligent;

(3) early humans had superior language abilities, and had better social organisation (Cochran and Harpending 2009: 25–26);

(4) and some suggest that early humans might have spread some bacteria or parasites which they had immunity against, but against which Neanderthals had not evolved immunity (Cochran and Harpending 2009: 28).
These are suggested explanations, though some may be wrong.

In any case, humans replaced Neanderthals and a revolution in material culture happened in the Upper Paleolithic in certain places like Europe where from 30,000 to 40,000 years ago humans invented all sorts of new tools and weapons, textiles, cave paintings, sculpture, and jewellery, as well as engaging in more long-distance trade (Cochran and Harpending 2009: 30). In Europe, this was called the Aurignacian culture (from c. 41,000–c. 26,000 BC), as well as the earlier Châtelperronian culture in central and south-western France and northern Spain (c. 43,000–c. 38,000 BC).

Such a revolution in material culture required a new propensity for invention, innovation and intelligence that was mysteriously absent in earlier periods of human evolution. Why did this happen?

Cochran and Harpending propose that this came about by the interbreeding of humans with Neanderthals in Europe and parts of Asia (Cochran and Harpending 2009: 36), though it did not happen in Africa. They propose that Neanderthals gave to early humans certain alleles (gene variants) which became common and conferred not only the ability to tolerate the cold or resist local diseases (Cochran and Harpending 2009: 54), but also new and advantageous cognitive abilities (Cochran and Harpending 2009: 56–57). They suggest that the gene microcephalin (MCPH1) that regulates brain size and the FOXP2 allele that has a role in speech and language abilities might have been acquired from Neanderthals (Cochran and Harpending 2009: 62–63).

Neanderthals had evolved bigger brains, and this may well have meant a greater level of cognitive ability and intelligence in certain ways, which were useful in hunting big game and in the colder, harsher environment of Europe (Cochran and Harpending 2009: 55).

So Cochran and Harpending argue that after c. 50,000 years ago early humans outside Africa – especially in Europe – acquired new, useful and greater cognitive abilities from admixture with Neanderthals, which was a genetic precondition for the cultural revolution of the Upper Paleolithic peoples (Cochran and Harpending 2009: 64).

This thesis is one of the more controversial aspects of The 10,000 Year Explosion, and other scientists argue that, while interbreeding did occur, it was rare and biologically and genetically unimportant (Cochran and Harpending 2009: 40).

It appears that, while early humans in Eurasia did interbred with the Neanderthals (and Neanderthals had in turn evolved from Homo erectus populations) (see here), the Neanderthal genetic contribution to modern Europeans is low: some put it as low as 1.5–2.1% (Prüfer et al. 2014). (For a useful family tree, see here). By contrast, Lohse and Frantz (2014) found that Neanderthal admixture occurring in ancient Eurasia was at a higher rate of 3.4−7.3%.

This remains a controversial issue, and here is some recent evidence in the videos below:

Also, some speculation on Neanderthal intelligence:

At any rate, because early humans developed better hunting techniques, required less food than Neanderthals, and had a more varied diet – that is, because they were more successful in evolutionary terms and better adapted to their environment – this led to greater population density than in previous human societies (Cochran and Harpending 2009: 33), and greater population density in turn allowed more mutations and more random creation of better traits by sexual reproduction in early human populations on which selection and evolution could work.

Finally, here is a chronology of events in prehistory relevant to the issues in Chapter 2 of The 10,000 Year Explosion:
300,000–250,000 – Homo heidelbergensis evolves into Neanderthals outside Africa

c. 158,000–38,000 BC – the Mousterian (or Mode III) culture or archaeological industry, of flint tools mainly associated with the Neanderthals, and some early humans, in Eurasia

125,000 years ago – Homo sapiens reached the Near East, but evidence suggests they retreated back to Africa, as their settlements were replaced by Neanderthals

108,000–9,700 BC – last Ice Age

c. 73,000 BC (± 900 years) – Lake Toba supervolcanic eruption (in Sumatra, Indonesia). This is the largest known explosive eruption on Earth in the last 25 million years. According to the Toba catastrophe theory, it had global consequences for human populations: it killed most humans living at that time and is believed to have created a population bottleneck in central east Africa and India, which affects the genetic make-up of the human world-wide population to the present

75,000 years ago – Homo sapiens left Africa again about across the Bab el Mandib, connecting Ethiopia and Yemen into Middle East

60,000–50,000 BC – outside Africa, Homo sapiens lives in Near East, Greece, south Asia, New Guinea and Australia

c. 58,000 BC – most areas north of the tropics not inhabited by Homo sapiens because of the cold and difficulty of food supply

c. 50,000–40,000 years ago – southeast Asians reach Australia; in Australia by 46,000 years ago at the latest

c. 43,000–41,000 BC – Cro-Magnon Homo sapiens reached Europe from the Near East, eventually replacing the Neanderthal population by 40,000 years ago

c. 43,000–c. 38,000 BC – the Châtelperronian culture in central and south-western France and northern Spain

c. 41,000–c. 26,000 BC – the Aurignacian culture is found in Europe (probably associated with GoyetQ116 type people), the archaeological culture of the Upper Palaeolithic; this first appears in Eastern Europe around c. 41,000 BC, and spread into Western Europe c. 38,000 and 34,000 BC, but replaced by the Gravettian culture c. 26,000 to 24,000 BC

39,000–37,000 BC – Neanderthals die out in Europe

35,000–12,000 BC – European hunter-gatherers descend from a single ancestral population with no significant genetic inflow from other regions

c. 29,000–c. 22,000 BC – the Gravettian tool-making culture of the European Upper Paleolithic of Vestonice cluster type people; ice age glaciation seems to have wiped out Gravettian culture people c. 22,000 BC

28,000 BC – East Asia was reached by Homo sapiens

28,000–13,000 BC – last cool phase of the Ice age; humans withdraw from north Eurasia to more southerly areas

c. 27,000–18,000 BC – Last Glacial Maximum (when the ice sheets were at their greatest extension) c. 24,500 BC; deglaciation began in the Northern Hemisphere gradually from c. 18,000 to 17,000 BC

26,000 BC – last group of Neanderthals disappear from southern Spain
The blog of Gregory Cochran and Henry Harpending:
West Hunter
Cochran, Gregory and Henry Harpending. 2009. The 10,000 Year Explosion: How Civilization Accelerated Human Evolution. Basic Books, New York.

Lohse, Konrad and Laurent A. F. Frantz. 2014. “Neandertal Admixture in Eurasia Confirmed by Maximum-Likelihood Analysis of Three Genomes,” Genetics 196.4: 1241–1251.

Prüfer, K. et al. 2014. “The Complete Genome Sequence of a Neanderthal from the Altai Mountains,” Nature 505.7481: 43–49.

Thursday, July 20, 2017

The 10,000 Year Explosion, Chapter 1: A Summary

Gregory Cochran and Henry Harpending’s The 10,000 Year Explosion: How Civilization Accelerated Human Evolution (2009) is a truly extraordinary book that every person on the Left should read. Critical reviews of the book can be found in Wills (2009), Arden (2009) and Gorelik and Shackelford (2010).

In essence, Cochran and Harpending challenge the notion that human evolution stopped around 50,000 years ago.

In Chapter 1 of The 10,000 Year Explosion, Cochran and Harpending (2009: 1) argue that
(1) human evolution has actually been accelerated by various pressures and historical developments over the past 10,000 years, as the environments and niches occupied by human beings radically changed, and

(2) that evolution in human beings has been about 100 times faster in the past 10,000 years than the long-run, average rate during all 6 million years of human and hominid evolution (Cochran and Harpending 2009: 23, citing Hawks et al. 2007).
The view that Cochran and Harpending oppose is as follows: the idea that the last stage of significant human evolution occurred between about 50,000 to 40,000 years ago and then ceased. That is to say, from 50,000 to 40,000 years ago during the Upper Palaeolithic humans went through a flowering of culture and material culture (such as weapons, tools, art and clothing), but then human evolution of the mind and body, in significant ways, ended around this time, and modern humans are essentially the same as humans of about c. 40,000 years ago (Cochran and Harpending 2009: 2).

The assumption lying behind this is that the environment occupied by humans became basically static about 50,000–40,000 years ago, and so no great new selective pressures caused by new environments continued to modify the human genome and phenotypes (Cochran and Harpending 2009: 2). Such a scenario is not impossible if a species occupies an environment that is stable: e.g., horseshoe crabs today are probably genetically and phenotypically much the same as horseshoe crabs 100 million years ago, because these organisms have occupied the same stable, static environment.

But Cochran and Harpending (2009: 3) contend that this assumption about the environments occupied by humans within the past 40,000 years – and especially the last 10,000 years – cannot possibly be taken seriously.

Instead, the evidence suggests that, while many species may well exist for long periods in stasis in stable environments, they can then easily be subject to rapid evolution in response to rapid environmental and selective pressures from natural selection (Cochran and Harpending 2009: 5, 19). For example, modern breeds of dogs have been created very recently in the space of about 15,000 years by human beings through artificial selection and breeding: to take one example, we have been able to change wolves into chihuahuas.

Changes can also happen rapidly in cognition or behaviour, e.g., domesticated dogs are significantly different in their cognitive and behavioural characteristics from wolves. And the Russian scientist Dmitri Belyaev was able to breed domesticated foxes from wild foxes in about 10 years of selective breeding (Cochran and Harpending 2009: 7), as described in this video:

Cochran and Harpending point to the following reasons for rejecting the stable environment hypothesis with respect to humans over the past 40,000 years:
(1) even after 40,000 years ago, humans continued to migrate around the surface of the planet, into southeast Asia, Australia, Europe, and also into northern Eurasia, Japan, and the Americas, where they experienced different environments and different evolutionary pressures for the following 10,000s of years, and, above all, some experienced the extremely harsh environment of the last Ice Age in the area of northern Eurasia (the last phase of which was the Last Glacial Maximum when the ice sheets were at their greatest extension from 27,000–18,000 BC).

(2) humans outside of Africa encountered and competed with other archaic humans such as the Neanderthals and Denisovans, as well as new animals and pathogens in these environments. Humans outside of Africa also interbred with Neanderthals and acquired a small amount of Neanderthal DNA.

(3) differential cultural and technological development occurred in these different regions, which in turn caused new selective pressures on the people in various areas, e.g., spears and arrows drove selection for faster, lighter humans who could hunt more successfully with these weapons (Cochran and Harpending 2009: 3).

(4) the agricultural revolution from c. 10,000 BC and the emergence of cities also created radically new environments from those inhabited by hunter gatherers before this time.

(5) as human populations rose with farming, mutations and beneficial individual traits caused by genetic mixing in sexual reproduction were more likely to occur (and then spread in these populations) than in much smaller populations of hunter-gatherers. And, importantly, even comparatively minor genotypic changes in alleles or gene variants, but occurring more frequently, can cause very profound and deep phenotypic changes quite rapidly in a species.
In short, Cochran and Harpending contend that these different environments have continued to shape human beings and even accelerate human evolution well after 50,000 years ago, and that even minor changes in allele frequencies in different human populations driven by selective pressures have caused phenotypic differences in external appearance, morphology, metabolism, defence against infectious diseases, and even cognitive and behavioural traits (Cochran and Harpending 2009: 19, 22).

This of course means not only that human beings of around 100,000 years ago were different from human beings c. 40,000 years ago, but also that humans c. 40,000 years ago or even 10,000 years ago were phenotypically different – in significant ways – from human beings alive today (Cochran and Harpending 2009: 18–19).

Cochran and Harpending (2009: 18–19) also contend that accelerated human evolution means that even humans in historical times from around 1,000 BC should be regarded as different – both genotypically and phenotypically – from us today. This has profound implications for our understanding of human history, and our understanding of why and how humans historically developed in terms of their cultures, technologies, economies, and social organisation.

To end with some concrete examples: most Europeans today are lactose-tolerant into adulthood. Europeans are generally lactose-tolerant because they have a mutation that allows the synthesis of lactase – an enzyme that digests milk sugar. But this evolutionary trait is quite recent: it only spread amongst Europeans from 3,000 to 2,000 BC as Indo-European-speaking Yamnaya-culture people from what is now southern Russia migrated into Europe and spread this mutation that they had evolved (Allentoft et al. 2015: 171). Before about 3,000 BC, Europeans were not lactose-tolerant into adulthood.

And if we went back in time to Europe of about 40,000 BC, we’d discover that Europeans of that era looked quite different from their modern descendants: e.g., they would have had heavy brow ridges, prognathism from the much larger teeth that humans had before the Neolithic farming revolution, and probably much darker skin.

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

Arden, Rosalind. 2009. Review of The 10,000 Year Explosion: How Civilization Accelerated Human Evolution by Gregory Cochran and Henry Harpending, Twin Research and Human Genetics 12.4: 409–410.

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

Gorelik, G. and T. K. Shackelford. 2010. Review of The 10,000 Year Explosion: How Civilization Accelerated Human Evolution by Gregory Cochran and Henry Harpending, Evolutionary Psychology 1: 113–118.

Hawks, John, Wang, Eric T., Cochran, Gregory M., Harpending, Henry C. and Robert K. Moyzis. 2007. “Recent Acceleration of Human Adaptive Evolution,” Proceedings of the National Academy of Sciences of the United States of America 104.52 (December 26): 20753–20758.

Wills, Christopher. 2009. Review of The 10,000 Year Explosion: How Civilization Accelerated Human Evolution by Gregory Cochran and Henry Harpending, New Scientist 201.2695: 46–47.