Saturday, December 1, 2007

Spencer Wells/THE JOURNEY OF MAN


A history of the migration of homo sapiens out of Africa and to our various other pockets of the world. The author, a genetic biologist, uses information gleaned from studies of polymorphisms on the Y chromosome (hence, the journey of MAN) to determine how long people have been where and which other groups they are most closely related to. The results are fascinating.

The text is heavy slogging at times, particularly at the beginning in the chapters that introduce polymorphisms--the author explains basic things like what a neutron is, but then is really rather light with explaining heavier stuff in a way that readers who are new to the subject would appreciate. (I took some genetic and evolutionary biology in college, and I still found myself having to step back and re-read many passages.) However, the interesting and quotable information that does come through made it worthwhile for me.

Here are some examples of some of the things I found interesting:

-There is most genetic diversity within populations than between them. 85% of genetic diversity is represented in all populations, things we can't see--like immune systems. Genetic evidence proves that all the physical differences we're so keen to take stock of are strictly topical.

-We are not descended from Neanderthals. For awhile, in fact, we co-existed. Neanderthals had their own exodus out of Africa over the million years preceding the human exodus (a million years is an amazingly long time for them to have bipedaled the earth if you think about the fact that modern humans have only existed for 50,000 years). There is no genetic evidence of any intermingling between humans and Neanderthals. Some scientists hypothesize a genocide scenario in which humans killed off the Neanderthals, but most think the Neanderthals just declined in number slowly and became extinct because they weren't as smart as us and couldn't make as many babies.

-The reason humans are such evolutionary winners is because we never adapted to our surroundings. Sounds counterintuitive, right? The thing is that when animals evolve to succeed in their environment, they make themselves highly vulnerable when the environment changes. And human beings haven't evolved in any meaningful way except one--their brain size. We have nothing except that. And apparently that's all we need. Awesome.

-The large brain size that sets us apart from everything else (including Neanderthals) occurred in what the author and others called "The Great Leap Forward" (thanks, Mao). The Great Leap happened in that community in northern Africa right before the migration out and can probably be pinpointed by--this is awesome--sentences with subjects, objects, AND verbs. Apparently, studies have shown that monkeys (and parrots, and other things) can memorize and understand words to an extent of "eat apple" or "monkey eat." But the breakdown occurs at "monkey eat apple"--human brains are the only ones that can make that leap. So cool.

-All the non-African men in the world and most African men are descended from one (1) single man. They all have the same guy's Y chromosome. He lived about 50,000 years ago in northwest Africa. So brotherhood of man, indeed.

-The only people in the world who don't have this Y chromosome are some African groups whose ancestors lived in the south of that continent. That means there is exponentially more genetic diversity among African populations than there is between, say, an Indonesian and a Welshman. There's also more in common between a man with the north African marker and either the Indonesian or the Welshman than there is between the man with the north African marker and a man with the south African marker.

-The oldest (longest-established) non-African people in the world are... Australians. They made their way along the coasts of India and Southeast Asia until they got to Australia about 45,000 years ago. They probably left archeological evidence along the way, but since the sea was 200 kilometers farther out back then all their remains are probably under water.

-Gene markers of modern populations can show cultural habits of ancient populations. One example: we know that Australians passed along the Indian Ocean coasts for thousands of years, yet there are no Australian Y chromosome markers at all in the southern Indian population, despite some archeological record of their presence. At first glance, you'd guess that this means ancient Australians and southern Indians never intermarried. But if you look at placental mitochondrial DNA (obviously found only in the female population), there is a lot of overlap with the Australian equivalent. The revised thesis: southern Indian men took Australian wives from the migrant coastal people, but few (or none) of the migrant men stayed in India or took Indian wives with them on their journey. This is in line with other facts mitochondrial and Y chromosome DNA reveal about the Indian caste system--men were basically locked into the caste they were born into, but women sneakily married up or down much more frequently. Wells makes a Verdi joke in this story: La Donna e Mobile. I found this highly entertaining.

4 comments:

Wayne said...

It's tough material to cover and keep interesting at the same time. I prefer the simplicity of Bill Bryson's Short History of Nearly Everything.

Church Lady said...

This must've been an intense read. I don't think I could slog through an entire reading, but I think I'd like to own this book as a reference. Something to read in shorter sittings.

Thanks for the great review!!

Alan said...

Wow!this is pretty heavy stuff but fascinating, to be sure. I read your review three times and I want to learn more. Thank you

April's Place said...

I would definitely recommend this book, if you have any interest in genetic geneology. It is written in a manner that is easy to understood. Please check my website if you have an interest in this topic, I have quite a few items on the subject and the genographic project.