Friday, January 10, 2014

"Ancestral Journeys" by Jean Manco

"Amusing review you wrote on your blog about Ancestors."


"That great tome you've been reading for days now. I read your review. It made me laugh."

"I haven't written a review yet."  (Baffled).

"Well, it was on the screen."


 "It was Greg Cochran's review you read, on his blog 'West Hunter'. I was reviewing it before writing my own thoughts."

I am of course immensely flattered that my wife might believe that a review by such an eminent population geneticist, polymath and all-round smart person could possibly have been written by myself. In her defence, she's not fantastically up on genetics or the deep history of Europe. She's right about the quality of the writing though: here's what Gregory Cochran had to say.
"Jean Manco has a new book out on the peopling of Europe, Ancestral Journeys.  The general picture is that Europeans arise from three main groups: the Mesolithic hunters (Hyperboreans),  Levantine farmers, and Indo-Europeans off the steppe.   It’s a decent synthesis of archaeological, linguistic, and genetic evidence. I suspect that her general thesis is in the right ball park:  surely not correct in every detail, but right about the double population replacement.

"It is a refreshing  antidote to previous accounts based on the pots-not-people fad that originated back in the 1960s, like so many other bad things.  Once upon a time, when the world was young, archaeologists would find a significant transition in artifact types, see a simultaneous change in skeletons,  and deduce that new tenants had arrived, for example with advent of the Bell Beaker culture.  This became unfashionable: archaeologists were taught to think that invasions  and Völkerwanderungs were never the explanation, even though history records many events of this kind.

"I suppose the work Franz Boas  published back in 1912, falsely claiming that environment controlled skull shape rather than genetics, had something to do with it.  And surely some archaeologists  went overboard with migration, suggesting that New Coke cans were a sign of barbarian takeover.  The usual explanation though, is that archaeologists began to find the idea of prehistoric population replacement [of course you know that means war - war means fighting, and fighting means killing] distasteful and concluded that therefore it must not have happened.  Which meant that they were total loons, but that seems to happen a lot.

"But the book could be better. Jean Manco relies fairly heavily on mtDNA and Y-chromosome studies, and they are not the most reliable evidence.  Not because the molecular geneticists are screwing up the sequencing, although there must sometimes be undetected contamination, but because mtDNA and Y-chromosomes are each single loci with an effective population size four times smaller than autosomal genes.  They are more affected by drift, and drift can deceive you.  Moreover, in some cases selection might affect the historical trajectory of mtDNA and Y-chromosomes,  which would add to the confusion. Now to be fair, we have more ancient mtDNA results than autosomal DNA,  and there is more published data on mtDNA and Y-chromosome than autosomal DNA in existing populations.  This situation is rapidly improving.

"Autosomal DNA has zillions of loci and a larger effective population size.  Most of it is neutral.  That’s what you want, for investigating past mixing and movement  – and autosomal DNA yields interesting hints using publicly available data and software.  For example, using the program ADMIXTURE, you find a West Asian-like component in almost all Europeans (from Spain to Russia, and at about the same level) – but not in Sardinians or Basques. Which must be telling us something.

"In addition, she’s not bloody-minded enough. She thinks that a fair fraction of the big population turnovers involved migrants moving into areas that had been abandoned by the previous owners. I can imagine that happening in a few cases.  Maybe the Greenlanders, living in an extremely marginal country for their kind of dairy farming, mostly left and/or died out  before the Eskimos showed up.  That is, in my dreams, because we know that the two groups fought. The Greenlanders may have been in trouble, but they didn’t just fall -  Eskimos pushed. The European colonization of the New World is closer, since there was a dramatic population collapse from the newly introduced Eurasian and African diseases, but even then there was a fair amount of fighting. I’m sure that there were serious epidemics in European prehistory, but  it seems unlikely they compared with the impact of the simultaneous arrival of  bubonic plague, diphtheria, leprosy, malaria, measles,  typhoid, and whooping cough on the Amerindians (with yellow fever and cholera for dessert).

"I mean, when the first farmers were settling Britain, about 4000 BC, they built ditched and palisaded enclosures.   Some of these camps are littered with human bones – so, naturally, Brian Fagan, in a popular prehistory textbook, suggests that ”perhaps these camps were places where the dead were exposed for months before their bones were deposited in nearby communal burials”!  We also find thousands of flint arrowheads in extensive investigations of some of these enclosures, concentrated along the palisade and especially at the gates.  Sounds a lot like Fort Apache, to me.

"There are some new and fascinating results about European prehistory that beg to be incorporated in a revised version of this book, for example the stuff about how the Hyperboreans contributed to the ancestry of modern European and Amerindians, but that info is so new that she could not possibly have incorporated it. Not her fault at all.

"Read it."
I'd classify "Ancestral Journeys" as a semi-popular book. Jean Manco's mastery of the details of populations and their movements across Europe, North Africa and the Near East across a time period stretching from 46,000 years ago to the early mediaeval is truly staggering - she seems to have absorbed and synthesised hundreds of sources. Somehow the clarity of her thinking and the organisation of her material saves the reader from being totally lost in the details.

The study of deep history is a fusion of archaeology, linguistics and genetics with the genetics becoming more important as more DNA samples - ancient and modern - are sequenced. What does this genetic information actually mean? The reader will need to internalise the historical evolution and mutation of mitochondrial and Y-chromosome DNA to understand the resulting haplogroup trees which drive historical analysis.

Evolutionary Tree of Y-DNA haplogroups (from Wikipedia)

If you've not had a course in population genetics then you will be hitting Wikipedia hard (you could do worse than start here and follow the links to grasp the genetic concepts underpinning this book).

Trivia point: Jean Marco is based just up the road from where we live, in Bristol.