Tuesday, September 18, 2012

Dirt Tells The Story

Usually, archaeologists are mostly concerned about what they can dig up out of the dirt.  But, sometimes the dirt itself also tells a story. 

A recent example comes from ongoing research into prehistoric Copper Age and Bronze Age structures and Bell Beaker culture artifacts in Southern Portugal.  This archaeological evidence is found in a well defined geographic region within Southern Portugal.  Why is this the case?

It turns out that the area where this evidence has been found is notable for "its geological diversity and good soils and plains" while the adjacent areas where these structures and artifacts are mostly absent are marked by a "poor littoral sandy platform."  Thus, the places that have dirt that is good for farming were home to this well developed prehistoric Iberian civilization, while this civilization didn't settle adjacent areas with dirt that is ill suited for farming.

As one of the researchers involved in this investigation, A.C. Valera, explains, there is still more work to be done in order to better understand the details:

[D]uring Neolithic and Chalcolithic . . . the different geological and ecological conditions naturally contributed to different human strategies of occupations (and, please, I am not talking about any kind of geographic determinism). So, in a general common frame of Southwest Iberia, we can see diversities and local and sub-regional specificities in interaction. Establishing the terms of these interactions is an actual target for reasearch.

Why care?

Because the sites that A.C. Valera and his team are investigating in Southwestern Iberia sheds light on what was going on at the proximate source, in time and place, of the biggest demographic transition in European history that your professors in college never told you about.  They didn't know until recently that it even took place.

The Old Conventional Wisdom Was "Pots Not People."

We have known for a long time when farming and herding commenced in Iberia (two or three thousand years after it did in the Fertile Crescent, give or take) and that the crops and domesticated animals used by early farmers and herders in Iberia were mostly domesticated in the Fertile Cresecent.  This event is called the arrival of the "Neolithic revolution" in the area. 

Few thousand years later, starting around the 8th century BCE, the archaeology of the region can be tied into historical accounts of the Celto-Iberians and some ancient relatives and predecessors of the Basques in Northeastern Iberia, and possibly some other populations.  Using archaeology to look at the immediate predecessors of the civilizations documented historically can stretch the relatively solid ground of historical knowledge back a few centuries more, but not all of the way back to the Bronze Age.

For a long time, the prevailing assumption was that the events in between were mostly gradual evolutions from one point to the other.  The archaeological cultures that existed in between have been classified into distinct groupings in particular places and time periods.  But, it has been unclear which dividing lines between archaeological cultures were most abrupt, when (if ever) there were major demographic transitions (for example, due to population replacement or mass migrations), and what the underlying logic drove transitions from one archaeological culture to the next.

In the 1970s, the prevailing orthodoxy regarding the transitions in archaeological cultures of Europe had been summed up in the motto "pots not people."  The understanding was that cultural technology transfers were more important than mass migrations in bringing about the transitions from one archaeological culture to the next.

Genetics Uprooted Conventional Wisdom About The Neolithic Transition.

Ancient DNA evidence has now made clear that there was a major demographic transition probably due to populations migrating into Europe as they brought farming and herding lifestyles to the region.  In much of Europe, this demographic transition was much more abrupt than had widely been believed

The modern evidence, particularly from population genetics and ancient DNA samples, makes clear that this was wrong.  Generally speaking, the story is of "pots and people" moving together.

The transition from hunting and gathering to producing food from domesticated plants and animals didn't necessarily give rise to a complete population replacement, but the demographic component of the transition was far larger than conventional wisdom had supposed before genetics were brought to bear on the question.

In twenty-twenty hindsight, it isn't terribly surprising that people who can product their own food from domesticated plants and domesticated animals might have a decisive edge over the hunter-gatherers who preceded them, and that in a pre-literate era, that these transitions might have needed whole populations of people migrating with their seeds and animals to take place.

Genetics Has Revealed A Post-Neolithic Demographic Transition.

Even more surprisingly, ancient DNA evidence is making it increasingly clear that there was at least one other major demographic transition (and quite possibly two) between the arrival of the first farmers and the beginning of written accounts of European history in the Iron Age. 

Ancient DNA from middle to late Iron Age burial sites in most of Europe show a population genetic mix in Europe that looks a lot like that of modern Europeans in the same regions, and very unlike that of the earliest available ancient DNA from prehistoric European hunters and gatherers in the Upper Paleolithic era.  But, ancient DNA from the earliest farmers in much of Europe (i.e. the earliest Neolithic) doesn't match either the prehistoric European hunters and gathers that preceded them, nor the Iron Age populations that followed them.  Sophisticated statistical analysis of the autosomal genetics of modern European populations confirm and elucidate the ancient DNA findings.

It was far less obvious, before this ancient DNA evidence became available, that one group of prehistoric people who had the ability to produce food with domesticated plants and animals could have such a dramatic demographic impact on another prehistoric population that could also produce its own food.

The Bell Beaker Culture Is A Likely Source Of The Post-Neolithic Demographic Transition.

A distinctive archaeological Bell Beaker culture starts to appear in Europe in the Chalcolithic era (i.e. Copper Age).  Radiocarbon dating confirms the inference arising from the presence of metals in Bell Beaker contexts and also allows archaeologists to accurate determine which Bell Beaker sites are the oldest.  The radiocarbon dated Bell Beaker archaeological finds put the origin of this archaeological culture sometime between 3000 BCE and 2500 BCE in Southern Iberia, although where the people who were involved in appearance of this culture came from is less clear. 

This Bell Beaker culture increasingly looks like a major source of the demographic transition that took place sometime between the arrival of the first farmers of Western Europe and the populations who lived there by the time that Roman historians started to arrive on the scene to document the situation. 

There are only so many archaeological cultures in right time frame that have been identified to date. In Europe, there has been enough archaeological research to assure us that this list of archaeological cultures is pretty much complete.  And, many of the archaeological cultures which are in the right time frame are a poor fit to the geographic scope of this demographic event, or are less attactive candidates because they show more continuity with prior archaeological cultures where they are found and were accompanied by a less distinctive break with previous archaeological cultures. 

The fact that Bell Beaker era human skeletal remains show differences in physical type of prior populations in many places is particularly telling.  While a difference in physical type could be due, for example, to changes in diet rather than mass migrations, any mass migration that did happen would be expected to produce some shift in the physical type seem in skeletal remains.

Put another way, the modern genetic mix found in Western Europe wasn't really in place until the Bell Beaker culture swept across the region (and perhaps as late as the early Iron Age in much of Europe, if there was more than one major prehistoric, post-Neolithic, demographic transition).  Many of the ancestors of modern Western Europeans probably arrived in Western Europe together with the Bell Beaker culture.

Portugal, where the Western and Northern European Bell Beaker culture apparently emerged around 2900 BCE and seems to have radiated from, is the natural place both to look forward and identify the elements of this archaeological culture that caused the descendants of these people to transform Western Europe, and is also the nature place to look backward and identify the source of this new cultural transformation and the population that delivered it. 



Maju said...

I think you got it all wrong: the sandy platform of the Baixo Alentejo does have some Bell Beaker, even if maybe less dense, where there is less BB is in the schist craton of the South (Algarve and some parts of Baixo Alentejo), which incidentally is a geological block that arrived from Newfoundland. That is probably because a non-Megalithic people shrouded in mystery but probably precursor of the later Tartessian language zone was already intruding there (i.e. the "horizons", which expanded northwards in the Bronze Age) and not because of the soil.

What the soil may explain is the intensity of the occupation, which is, since Neolithic, much greater in the Middle Guadiana banks.

Also you are beating the dead horse of Bell Beaker replacement but something discussed in those entries at Valera's blog is that BB is anything but an intrusive culture which could cause such population replacement, instead it is a complex phenomenon, in most cases just a late fashion within the much older Dolmenic Megalithism.

Dolmenic Megalithism that precisely was born in those lands of Alentejo, 70000 years ago, right after the first Neolithic, later expanding Northwards, in what is also probably a complex history but one that had many more opportunities to cause demic replacements and massive founder effects (unlike BB).

So exactly the opposite, if anything.

This Megalithic expansion could explain the scatter for example of mtDNA H1, first documented in Neolithic Portugal.

Andrew Oh-Willeke said...

For reference of anyone reading this post later, even though I know that it is just a typo, I am certain that Maju meant 7,000 years ago and not 70,000 years ago, in his comment and I wouldn't want anyone less familiar with the topic to be misled.

Curious what your thoughts are on the Tartessian language/culture.

Maju said...

Of course, thanks. Whoa! Silly zeros!