It Began In Africa

Out Of Eden: The Peopling Of The World, Stephen Oppenheimer, ISBN 1841196975

This book concerns the peopling of the world by anatomically modern human beings - that is to say, us. It draws together evidence from archeology, the climate and, overwhelmingly, genetics to present an argument clear in the broad strokes but nonetheless finely detailed.

There are two kinds of genetic evidence that have only relatively recently become easy to gather, but have now been studied in sufficient detail to answer interesting questions. First is mitochondrial DNA which we inherit exclusively from our mothers; second is the Y chromosome, inherited exclusively from our fathers. By studying the variations in these two bodies of information between living people, we can construct a tree of life, and even attach rough dates to the branch points; and since people seem to be conservative about location, we can establish some of the geography of those branch points too.

Two conclusions seem to be pretty solid.

1. We are not descended from Neanderthals; indeed there is no evidence even of interbreeding. (Which doesn't mean it didn't happen at all, just that there can't have been very much.) It's too much of a coincidence to suppose that the Neanderthals coincidentally died off as our ancestors arrived in Europe; but whether we out-competed them, accidentally infected them with novel diseases, or even deliberately exterminated them, remains an unknown.

2. Modern humans evolved in Africa within the last 200K years, not all around the world, and (apart from a false start) there was only one prehistoric exodus from Africa, around 80K years ago, perhaps to what is now Yemen. Multiregionalism is dead.

The further from the root of the tree, the more speculative Oppenheimer's conclusions necessary become (as he happily admits). His story is of a rapid expansion along the coastline of southern Asia, colonizing Australia 70K years ago, a tremendous volcanic erruption temporarily dividing mankind in two and leaving a divide visible in the genetic tree to this day. From the coasts man penetrates into central Asia at various points and from there reaches Europe from 50K years ago onwards. The colonization of America becomes possible due to a major ice age starting 18K years ago.

The book is full of maps, which are generally clear, and tree diagrams, which tend not to be; the latter spend most of the available space on visually obstructive parallel lines, with the annotative text crammed in annoyingly small. While the subject of these diagrams is going to be inconvenient to fit on a page however presented, I do feel that it might have been possible to do better: perhaps a greater willingness to split the trees over a couple of pages. Making the lines angled rather than having every branch be a pair of right angles might have eliminated the distractive properties of the massed parallels, too (though admittedly that risks becoming inconveniently untidy in other ways).

Oppenheimer is not afraid to use abbreviations and relatively technical language. The excessively casual reader might thereby be put off, but I choose to interpret it as the author declining to insult the reader's intelligence and initiative. Similar remarks apply to the large amount of detailed argument concerning the interpretation of the genetic evidence.

He also attempts to be even-handed regarding alternative theories, though in a few cases (e.g. multiregionalism and what was at least until recently conventional wisdom concerning the colonization of the Americas) this falls through and he can't help but disagree point-blank. Clearly though there comes a point where the scales cease to balance, and while I'm not an expert in the field I didn't feel that the author had got it wrong.

As a final note, this book would be an excellent companion to Jared Diamond's Guns, Germs And Steel and I'd recommend that anyone who found one of these two books interesting should read the other.


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