Saturday, November 21, 2009

Before the Dawn

A book review I wrote for my own blog.

Book Review: Before the Dawn by Nicholas Wade

While not as all-encompassing as Jared Diamond's Third Chimpanzee or Richard Dawkins's Selfish Gene, I must say that this book left a very deep impression on me. As someone who has been interested in the unrecorded prehistory of man for a long time, I found this book to be something of a welcome update of what was started by the two titles I mentioned earlier. The Selfish Gene was published in 1976, The Third Chimpanzee in 1991. Since the mapping of the human genome in 2003, the results of many new studies have been released, shedding light onto what were once murkier areas in the gaps of what we know of the gene's influence on man and man's prehistory respectively. I really recommend this book for anyone interested on the subject.

The first couple of chapters consist of an introduction and then quick summarization of what would be a basic anthropology course. A highly accurate visual system was needed to help judge distances between trees properly and safely make leaps, such that nearly all primates view the world more or less exactly as we do. Opposable thumbs for a good, strong grip on branches and boughs of many sizes and shapes. Bipedal movement allowing a farther, more commanding view, the ability to carry things while moving, and also just a more energy efficient way of getting around when compared to the knuckle walk which was the common mode of movement before.

It is the following chapters, however, where the book really separates itself from the others, and while it does draw on past disciplines like archeology and paleolinguistics -again Third Chimpanzee but also Diamond's Guns, Germs, and Steel- for some of its historical conclusions, the recent genetic findings are what really distinguish it. An early example, the approximate dating of when humans first began wearing clothes, demonstrates how we can learn what was never before possible, provided we ask the right questions.

Dating the Development of Several Uniquely Human Charateristics

The louse, a parasite which cannot survive more than six to eight hours away from the warmth of a human body, was once confined to the tiny island of hair on the human head for a period of time between when man lost his body hair and began wearing clothing. This advent, it seems, gave rise to the body louse which had adapted its claws specifically to grasp clothing. By comparing either the Y chromosomes on males -which are passed unchanged and directly from fathers to sons- or mitochondrial DNA -passed unchanged from mothers to daughters- geneticists can now to come up with an approximate date for when species split into new branches. In this particular case, DNA from the body louse and the regular louse were both analyzed, showing a split of the two branches about 72,000 years ago, thus giving scientists that approximate date for the adoption of wearing clothes.

There were several other interesting revelations as well. An obvious next question might be to ask about the loss of body hair. A few possible reasons are given as to why it might have happened -the need to sweat to cool down the body, ridding oneself of parasites, preferences in sexual selection- but one thing that might be a little more certain is that darker skin developed from this advent as protection from the sun's ultraviolet rays which destroy folic acid, an essential nutrient. While our forebears' skin was almost certainly pale originally, as it is in chimps, dark skin would have been necessary to survive in the African sun without body hair to protect oneself. The melanocortin receptor gene which regulates skin pigmentation provides the key. By dating the divergence of this gene towards darker skin, an approximate date of 1.2 million years ago seems to be when humans lost most of their body hair.

The original ancestral population of humans who left Africa would've almost certainly had black skin. Paler skin confers an advantage to colder climates because it lets in more sunlight and allows for better synthesis of Vitamin D. It appears to have come about much later, after humans had left Africa and some were living in far colder temperatures to the north which would become even colder during a glacial period 20,000 years ago. The emergence of lighter skin, which occurs in both Asians and Europeans, developed twice, each time independently of the other.

New Data on the Human Diaspora out of Africa

Genetics have also allowed scientists to estimate that the approximate size of the original human population in Africa when some finally began their exodus out of the continent was about only 5,000, and that this occured about 50,000 years ago. From that number all people on this planet have emerged. Unlike previously believed, humans appear not to have taken the northern route out of Africa past Egypt and through the Fretile Crescent, but rather to have gone across the lower portion of the Red Sea which would've been about 100 feet lower at the time. The reason for this, probably would've been that the Fertile Crescent was already inhabited by Neanderthals who would've provided fiercesome competition for the early ancestors of man, and consequently had boxed them in, unable to leave Africa until that point.

Testing the genetics of modern societies shows that people in general have had a tendancy to live, marry and raise children in about the same area, a trend that has continued to this day but was even more pronounced before 100 years ago and the advent of modern transportation. From this data, early man seems to have crossed the Red Sea, then the southern tip of the Arabian Peninsula to India, then continued southward on landbridges existing at that time and primitive boats to Australia, populating on the way what are now some the Pacific Islands, the Phillipines, and New Guinea. The Australian Aborigines, New Guinea Highlanders and jungle dwelling Negritos of the Phillipines, Malaysia, and Adaman Islands appear to be the closest relatives of the Khoisan, who themselves represent one of the longest, most ancient branches of DNA amongst humans who stayed in Africa.

The primitive technology of early man was comparable with that of the Neanderthals, and due to that groups larger body size and stronger muscles, they would've made more than a formidable match. But the forebears of modern humans had a capacity for higher intellect, and perhaps coupled with their ability for more advanced language (a subject the book dwells on much more extensively), eventually were able to shape for themselves a more successful package of subsistence, environmental adaptation, weapons, and other artifacts. Thus the long struggle between the two began to turn against the Neanderthals as modern man began to slowly expand his territory, occupying more and more space that once belonged to Neanderthals until their extinction.

The question of whether humankind's early ancestors mixed and interbred with the Neanderthals has long vexed those who study them, but now at last seems to be finally getting put to rest. By extracting and examining a small sample of DNA from a Neanderthal specimen, a team from Munich managed to show that extremely little to no interbreeding occurred between the two species.

Some Final Considerations on Man's Evolution

In light of what new, genetic testing has taught us, the book makes many conclusions along the way to its destination. Of these, the most important is the thought that modern man has continued to evolve on the genetic level even since leaving Africa and all the way up to the present. It has long been generalized that the most important changes occurred before 50,000 years ago, at which point, man became "anatomically modern" and has remained in a state of genetic stasis ever since. This argument proceeded from the idea that man hasn't needed to adapt any further to his environment. But to assume this would be to assume that no other kind of strife plagued mankind up until today, and that no other accustomization was necessary.

The book delves further into the idea that mankind didn't just need to be "anatomically modern" to scale the heights of today, but also "behaviorally modern". In examining this, one has to consider that many aspects to the behavior of man had to be adjusted (the ability to trust others and consequently work with them, give up the individual freedom that a state of nature provides, adjust to sedentary life, etc...) One also has to begin considering how and what genes have an influence on these behaviors. Genes don't just determine physical characteristic like strength, height, skin, hair, and eye color, but also things like susceptibility to diseases, level of aggressive behavior, propensity to lie to others or cheat on one's partner, things some of which have traditionally been more associated with psychology than biology.

That mankind hasn't ceased to evolve on the genetic level might be most evident in the world of difference between how we lived 50,000 years ago and how we live now. How we shall proceed to evolve into the future might just depend on to what extent we are willing or able to harness genetic manipulation to further achieve our goals.

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