Book Club: The 10,000 Year Explosion: pt 4 Agriculture

Welcome back to EvX’s Book Club. Today we’re discussing Chapter 4 of The 10,000 Year Explosion: Consequences of Agriculture.

A big one, of course, was plague–on a related note, Evidence for the Plague in Neolithic Farmers’ Teeth:

When they compared the DNA of the strain recovered from this cemetery to all published Y. pestis genomes, they found that it was the oldest (most basal) strain of the bacterium ever recovered. Using the molecular clock, they were able to estimate a timeline for the divergence and radiation of Y. pestis strains and tie these events together to make a new, testable model for the emergence and spread of this deadly human pathogen.

These analyses indicate that plague was not first spread across Europe by the massive migrations by the Yamnaya peoples from the central Eurasian steppe (around 4800 years ago)… Rascovan et al. calculated the date of the divergence of Y. pestis strains at between 6,000 and 5,000 years ago. This date implicates the mega-settlements of the Trypillia Culture as a possible origin point of Y. pestis. These mega-settlements, home to an estimated 10,000-20,000 people, were dense concentrations of people during that time period in Europe, with conditions ideal for the development of a pandemic.

The Cucuteni-Trypilia Culture flourished between the Carpathian Mountains and the Black Sea from 4800-3000 BC. It was a neolithic–that is, stone age–farming society with many large cities. Wikipedia gives a confused account of its demise:

According to some proponents of the Kurgan hypothesis of the origin of Proto-Indo-Europeans … the Cucuteni–Trypillia culture was destroyed by force. Arguing from archaeological and linguistic evidence, Gimbutas concluded that the people of the Kurgan culture (a term grouping the Yamnaya culture and its predecessors) … effectively destroyed the Cucuteni–Trypillia culture in a series of invasions undertaken during their expansion to the west. Based on this archaeological evidence Gimbutas saw distinct cultural differences between the patriarchal, warlike Kurgan culture and the more peaceful egalitarian Cucuteni–Trypillia culture, … which finally met extinction in a process visible in the progressing appearance of fortified settlements, hillforts and the graves of warrior-chieftains, as well as in the religious transformation from the matriarchy to patriarchy, in a correlated east–west movement.[26] In this, “the process of Indo-Europeanization was a cultural, not a physical, transformation and must be understood as a military victory in terms of successfully imposing a new administrative system, language, and religion upon the indigenous groups.[27]

How does it follow that the process was a cultural, not physical transformation? They got conquered.

In his 1989 book In Search of the Indo-Europeans, Irish-American archaeologist J. P. Mallory, summarising the three existing theories concerning the end of the Cucuteni–Trypillia culture, mentions that archaeological findings in the region indicate Kurgan (i.e. Yamnaya culture) settlements in the eastern part of the Cucuteni–Trypillia area, co-existing for some time with those of the Cucuteni–Trypillia.[4]Artifacts from both cultures found within each of their respective archaeological settlement sites attest to an open trade in goods for a period,[4] though he points out that the archaeological evidence clearly points to what he termed “a dark age,” its population seeking refuge in every direction except east. He cites evidence of the refugees having used caves, islands and hilltops (abandoning in the process 600–700 settlements) to argue for the possibility of a gradual transformation rather than an armed onslaught bringing about cultural extinction.[4]

How is “refugees hiding in caves” a “gradual transformation?” That sounds more like “people fleeing an invading army.”

The obvious issue with that theory is the limited common historical life-time between the Cucuteni–Trypillia (4800–3000 BC) and the Yamnaya culture (3300–2600 BC); given that the earliest archaeological findings of the Yamnaya culture are located in the VolgaDonbasin, not in the Dniester and Dnieper area where the cultures came in touch, while the Yamnaya culture came to its full extension in the Pontic steppe at the earliest around 3000 BC, the time the Cucuteni–Trypillia culture ended, thus indicating an extremely short survival after coming in contact with the Yamnaya culture.

How is that an issue? How long does Wikipedia think it takes to slaughter a city? It takes a few days. 300 years of contact is plenty for both trade and conquering.

Another contradicting indication is that the kurgans that replaced the traditional horizontal graves in the area now contain human remains of a fairly diversified skeletal type approximately ten centimetres taller on average than the previous population.[4]

What are we even contradicting? Sounds like they got conquered, slaughtered, and replaced.

Then Wikipedia suggests that maybe it was all just caused by the weather (which isn’t a terrible idea.) Drought weakened the agriculturalists and prompted the pastoralists to look for new grasslands for their herds. They invaded the agriculturalists’ areas because they were lush and good for growing grain, which the pastoralists’ cattle love eating. The already weakened agriculturalists couldn’t fight back.

ANYWAY. Lets get on with Greg and Henry’s account, The 10,000 Year Explosion:

The population expansion associated with farming increased crowding, while farming itself made people sedentary. Mountains of garbage and water supplies contaminated with human waste favored the spread of infectious disease. …

Most infectious diseases have a critical community size, a  number and concentration of people below which they cannot persist. The classic example is measles, which typically infects children and remains infectious for about ten days, after which the patient has lifelong immunity. In order for measles to survive, the virus that causes it, the paramyxovirus, must continually find unexposed victims–more children. Measles can only persist in a large, dense population: Populations that are too small or too spread out (under half a million in close proximity) fail to produce unexposed children fast enough, so the virus dies out.

Measles, bubonic plague, smallpox: all results of agriculture.

Chickenpox: not so much.

I wonder if people in the old Cucuteni–Trypillia area are particularly immune to bubonic plague, or if the successive waves of invading steppe nomads have done too much genetic replacement (slaughtering) for adaptations to stick around?

Harpending and Cochran then discuss malaria, which has had a big impact on human genomes (eg, sickle cell,) in the areas where malaria is common.

In general, the authors play it safe in the book–pointing to obvious cases of wide-scale genetic changes like sickle cell that are both undoubtable and have no obvious effect on personality or intelligence. It’s only in the chapter on Ashkenazi IQ that they touch on more controversial subjects, and then in a positive manner–it’s pleasant to think, “Why was Einstein so smart?” and less pleasant to think, “Why am I so dumb?”

However:

It’s time to address the old chestnut that biological differences among human populations are “superficial,” only skin-deep. It’s not true: We’re seeing genetically caused differences in all kinds of functions, and every such differences was important enough to cause a significant increase in fitness (number of offspring)–otherwise it wouldn’t have reached high frequency in just a few millennia.

As for skin color, Cochran and Harpending lean on the side of high-latitude lightening having been caused by agriculture, rather than mere sunlight levels:

Interestingly, the sets of changes driving light skin color in China are almost entirely different from those performing a similar function in Europe. …

Many of these changes seem to be quite recent. The mutation that appears to have the greatest effect on skin color among Europeans and neighboring peoples, a variant of SLC24A5, has spread with astonishing speed. Linkage disequilibrium… suggests that it came into existence about 5,800 years ago, but it has a frequency of 99 percent throughout Europe and is found at significant levels in North Africa, East Africa, and as far east as India and Ceylon. If it is indeed that recent, it must have had a huge selective advantage, perhaps as high as 20 percent. It would have spread so rapidly that, over a long lifetime a farmer could have noticed the change in appearance in his village.

Wow.

In humans, OAC2 … is a gene involved in the melanin pathway… Species of fish trapped in caves… lose their eyesight and become albinos over many generations. … Since we see changes in OCA2 in each [fish] case, however, there must have been some advantage in knocking out OCA2, at least in that underground environment. The advantage cannot like in increased UV absorption, since there’s no sunlight in those caves.

There are hints that knocking out OCA2, or at least reducing its activity, may he advantageous… in humans who can get away with it. We see a pattern that suggests that having one inactive copy of OCA2 is somehow favored even in some quite sunny regions. In southern Africa, a knocked-out version of OCA2 is fairly common: The gene frequency is over 1 percent.

And that’s an area with strong selection for dark skin.

A form of OCA2 albinism is common among the Navajo and other neighboring tribes, with gene frequencies as high as 4.5 percent. The same pattern appears in southern Mexico, eastern Panama, and southern Brazil. All of which suggests that heterozygotes…may ave some advantage.

Here is an article on the possibility of sexual selection for albinism among the Hopi.

So why do Europeans have such variety in eye and hair color?

Skeletons

The skeletal record clearly supports the idea that there has been rapid evolutionary change in humans over the past 10,000 years. The human skeleton has become more gracile–more lightly built–though more so in some populations than others. Our jaws have shrunk, our long bones have become lighter, and brow ridges have disappeared in most populations (with the notable exception of Australian Aborigines, who have also changed, but not as much; they still have brow ridges, and their skulls are about twice as thick as those of other peoples.)

This could be related to the high rates of interpersonal violence common in Australia until recently (thicker skulls are harder to break) or a result of interbreeding with Neanderthals and Denisovans. We don’t know what Denisovans looked like, but Neanderthals certainly are noted for their robust skulls.

Skull volume has decreased, apparently in all populations: In Europeans, volume is down about 10 percent from the high point about 20,000 years ago.

This seems like a bad thing. Except for mothers.

Some changes can be seen even over the past 1,000 years. English researchers recently compared skulls from people who died in the Black Death ([approximately] 650 years ago), from the crew of the Mary Rose,a  ship that sank in Tudor times ([approximately] 450 years ago) and from our contemporaries. The shape of the skull changed noticeably over that brief period–which is particularly interesting because we know there has been no massive population replacement in England over the past 700 years.

Hasn’t there been a general replacement of the lower classes by the upper classes? I think there was also a massive out-migration of English to other continents in the past five hundred years.

The height of the cranial vault of our contemporaries was about 15 percent larger than that of the earlier populations, and the part of the skull containing the frontal lobes was thus larger.

This is awkwardly phrased–I think the authors want the present tense–“the cranial vault of our contemporaries is…” Nevertheless, it’s an interesting study. (The frontal lobes control things like planning, language, and math.) 

We then proceed to the rather depressing Malthus section and the similar “elites massively out-breeding commoners due to war or taxation” section. You’re probably familiar with Genghis Khan by now. 

We’ve said that the top dogs usually had higher-than-average fertility, which is true, but there have been important exceptions… The most common mistake must have been living in cities, which have almost always been population sinks, mostly because of infectious disease. 

They’re still population sinks. Just look at Singapore. Or Tokyo. Or London. 

The case of silphium, a natural contraceptive and abortifacient eaten to extinction during the Classical era, bears an interesting parallel to our own society’s falling fertility rates. 

And of course, states domesticate their people: 

Farmers don’t benefit from competition between their domesticated animals or plants… Since the elites were in a very real sense raising peasants, just as peasants raised cows, there must have been a tendency for them to cull individuals who were more aggressive than average, which over time would have changed the frequencies of those alleles that induced such aggressiveness.

On the one hand, this is a very logical argument. On the other hand, it seems like people can turn on or off aggression to a certain degree–uber peaceful Japan was rampaging through China only 75 years ago, after all. 

Have humans been domesticated? 

(Note: the Indians captured by the Puritans during the Pequot War may have refused to endure the yoke, but they did practice agriculture–they raised corn, squash and beans, in typical style. Still, they probably had not endured under organized states for as long as the Puritans.)

There is then a fascinating discussion of the origins of the scientific revolution–an event I am rather fond of. 

Although we do not as yet fully understand the true causes of the scientific and industrial revolution, we must now consider the possibility that continuing human evolution contributed to that process. It could explain some of the odd historical patterns that we see.

Well, that’s enough for today. Let’s continue with Chapter 5 next week.

How about you? What are your thoughts on the book?

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