In March I reviewed The 10,000 Year Explosion, by Gregory Cochran and Henry Harpending, which presents convincing evidence and discussion about how the human species continues to evolve. In one chapter they refer to a colleague's work and his book, Before the Dawn: Recovering the Lost History of Our Ancestors by Nicholas Wade. Naturally, I obtained the book and read it carefully.
To be up front here: Though I am a Christian, of a very evangelical and Biblical tradition, I am also a scientist, with perhaps way too much education in all the physical sciences; I finished my formal education at age 37. I wrote software for scientists for forty years. In retirement, I work for a natural history museum part time, both as a computer scientist and a biologist. At a young age I learned the "Gap theory" of interpreting Genesis and other parts of the Bible that refer to prehistory such as Job 38:4-7, Zechariah 12:1, and Isaiah 45:18. By careful study I determined that cosmology and deep time (13+ billion years of it), plus the facts of evolution and the theory of natural selection that describes how it operates, are no threat to Biblical faith nor to any revelation in the Bible.
Therefore, concerning people, the extreme Biblical literalist view is that humans (and all other living species) were created ex nihilo less than 10,000 years ago, and are the same now as they were then, barring various kinds of catastrophe and degeneration. Their creation was very shortly after that of the universe and Earth.
The scientific view is that once life on Earth began, natural selection operated for about two billion years to produce multicellular life from unicellular life, then the multicellular creatures continued evolving until all living forms we see today were produced, along with some ten, to 100, to even 1,000 times as many species that went extinct in past eons; then among the tiny twig on the "tree of life" known as Great Apes, one ape species split into three species, which continued to evolve and adapt to different environments to become humans, chimpanzees, and bonobos; along the way other species such as H. erectus and Neanderthals arose and later became extinct.
The combined view I have (following G.H. Pember and others) is that Genesis 1:1 occurred "in the dateless past", to quote C.I. Scofield, and that the first verb in Genesis 1:2 is "became": "The earth became waste and empty", where Isaiah 45:18 tells us the original formation of the planet was "not waste". Prior to historical time, "anatomical" humans, that were not "behaviorally modern", experienced a big change. Their worldwide spreading from a homeland in Africa began during a warm spell between ice ages about 50,000 years ago. That behavioral change probably marks a point in time that God intervened, as recorded in Genesis 2:7, "And the Lord God formed man of the dust of the ground, and breathed into his nostrils the breath of life; and man became a living soul." (King James Version). The grammatical emphasis is on the word "living". This does not describe a creation ex nihilo. "Dust of the ground", a metaphor for humanity, existed already, but when God breathed a spirit into "the man", the animal soul became a "living soul," a soul that is now able to contact God. The rest of the Bible describes contact after contact between God and various people. The Septuagint translates "living soul" as ψυχὴν ζῶσαν , "psuchen zosan", which refers to divine life, not biological life.
With all that in mind, I consider two questions:
- Do the mechanisms of natural selection still operate on humans?
- Do any changes thus wrought continue to improve our adaptation to modern environments, or are they only degradations from a formerly more perfect humanity? (as many Christians believe)
I look for well-researched books like Before the Dawn and The 10,000 Year Explosion to find answers to those two questions. With new genetic tools made available in the past twenty years, there is evidence aplenty that humans are still evolving, and that we continue to become better suited to the environments into which our travels have taken us. Further, genetics has led anthropologists and archaeologists to look more keenly at their own studies for things that were overlooked under an older paradigm that stated, "once humans developed culture, physical evolution came to a halt." It most assuredly did not!
I'll begin by discussing a few items I bookmarked. I can tell which chapter these are in, but the "page" numbers of the eBook don't correspond to printed pages. In the first chapter, after defining two periods of prehistory, the 5 million years since pre-humans split from other apes, and the 45,000 years between the time some left Africa and the development of writing, they ask,
"Why should the human genome, specifically shaped for survival in the present, have so much to say about the past?" (early in Chapter 1, "Genetics & Genesis")I immediately thought, "Only if 'the present' means 'the past 500-1000 years' can this question be meaningful." Actually, as the author goes on to discuss, our genome contains material that supported survival over the entire span, including some important genes that have been kept nearly unchanged for tens or hundreds of millions of years; also others that arose in the past few thousand and even the past few hundred years, and some that are "works in progress" right now.
More to the point, an allele (a specific form of a gene) that arose and became frequent long ago will contain "silent mutations" that can inform us of our history. Time for a side trip.
The Central Dogma of Genetics states that DNA is copied to RNA, and RNA is transcribed to chains of amino acids, which are peptides and proteins. Transcription takes place in a molecular machine called a ribosome. There are 64 3-letter codons of DNA or RNA. There are 20 amino acids. Thus, the "translation table" to convert an RNA codon into an amino acid has multiple entries for each amino acid. Only one amino acid, methionine, has a single code. The other 19 have two, three, or four codons that "mean" them. Thus, the codons GGU, GGA, GGC, and GGG all code for glycine. If something changes a GGG in your DNA to GGA, it won't change the amino acid that results. That is an example of a silent mutation.
We won't get into any of the many things that can cause such a change, but we all accumulate many in each of our cells in our lifetime. There are also other kinds of mutations, and some lead to new proteins. A mutation that is helpful in any way will be kept; one that is harmful will usually cause the death of the cell. Mutations that wind up in our gametes (sex cells), that didn't cause them to die already, can get into our children. We typically pass on about 50 mutations to each child. In a genome of a billion codons, 50 is not many.
The studies of what might have happened in the past depend on the rate at which silent mutations accumulate. Of course, it is possible for a silent mutation to re-mutate back the way it was, but the number of these will be very small, since point mutations are rare to start with (50 out of a billion per generation, per person). This principle is brought out numerous times in the book. End of side trip.
If we first look back 5,000,000 years or so, to the ancestor of humans, chimps, and bonobos, what would we see? There is scant fossil evidence. Central and east-central Africa were warm and humid then as they are now; there were no ice ages yet. In conditions like that, even teeth rot too quickly to leave fossils for us to find today. What little we know matches what we can infer by taking an "average hominin": the size of a chimp or smaller (males 50-100 kg, females 30-60 kg), furry like modern chimps, brain size similar to a chimp (450 cc) or maybe a bit smaller, promiscuous in sexual habits, possibly patriarchal but maybe not, and probably violently territorial and xenophobic. Today, bonobos are a little smaller than chimpanzees, equally furry, with a brain the same size, even more promiscuous, matriarchal, but less xenophobic and much less violent. Humans have become a little larger overall, and a foot or two taller, mostly hairless, but with much larger brains (1,400-1,600 cc), sexually more private but not necessarily less promiscuous, usually patriarchal (sorry, feminists), and with a great range of xenophobia and territorial aggression.
While chimps and bonobos are so physically similar that they were thought to be the same species until a generation ago, they are behaviorally very different. Further, humans are very, very different from both in many ways, but we can see our behavior reflected in theirs. It is almost as if we have a range of cultural expressions that encompasses all the variations found in bonobos and chimps.
Now look back 50,000 years, to the "behaviorally modern humans" (BMH) who left Africa to spread the world over. The archaic human species they encountered and what happened as a result are stories for another day. What were these "moderns" like? Between 100,000 (maybe 150,000) years ago and 50,000 years ago, the species (still called Homo sapiens) is called "anatomically modern humans" (AMH), and is physically very similar to "us, today", but with more archaic behavior. We will set aside for the moment the theological implication I made earlier about what may have happened 50,000 years ago. What is the difference between AMH and BMH? As I found upon reading later chapters, it's probably best to not consider us, today as BMH, but just "modern humans", MH, after another transition between 15,000 and 10,000 years ago. Both behavior and anatomy changed after that.
So, to get a BMH person, start with a very well-conditioned person, not quite an Olympic athlete, perhaps…or, what the heck, let's go with a couple of Olympians. We can pick the runner Usain Bolt (6' 5", 207 lb/195 cm, 94 kg) for the male, and gymnast Kylie Dickson (5' 6", 110 lb/167 cm, 50 kg) for the female. The BMH's were bare-skinned and lived in Africa, so the skin would be black. Shorten the male by several inches while leaving his weight the same. Double the strength of his muscles and bones, and add 20% to the thickness of his skull. Add 10-20 kg to the weight of the female, and make her bones and muscle proportionally greater. Both this man and this woman would look like modern weightlifters (the ones who don't use steroids). You wouldn't want to meet either one in a dark alley, unless perhaps you had a 5th degree Black Belt in Aikido. I have a Korean friend who is a 4th degree black belt; he doesn't need a weapon, he is a weapon. But he might not prevail against an average BMH male.
What else might be different? "Modern" behavior, to an anthropologist, is the more sophisticated late paleolithic toolkit that showed up about 50,000 years ago, along with sophisticated art (cave paintings being a stellar example), and more group interaction, including some tolerance of strangers so trading could be carried out. The story told by their bones, however, is of frequent and persistent combat and warfare. Although the women were also stronger than we'd find usual today, they didn't engage in combat, but had harder domestic work (like pulling hides off animals), than would have been usual later on.
So, back to, what differed between AMH and BMH? Not the anatomy, except perhaps in fine details. From 100,000 (or so) years ago until 15,000 years ago, the anatomy remained very similar. But better group dynamics, probably fostered by the development of language, seems to be a crucial step. It seems to me that sophisticated art had to follow language; once symbolic representation of thought was possible, other symbolisms including artistic artifacts could follow. The 10th chapter "Language" goes into this very comprehensively. Language seems to have appeared shortly before 50,000 years ago, and much else followed.
Chapter 7, "Settlement", brought out something that surprised me: the author's contention (he is far from alone in this) that people began to settle down into communities as much as 5,000 years before agriculture. I'd thought it was the other way around, and I've read that numerous times. I can't debate the point, so I'll leave it to you to read what the author has to say. But it convinced me. Starting before 15,000 years ago, a few thousand years of warming were followed by more cold, that broke about 11,500 years ago. The coldest bit was the Younger Dryas period, which lasted 800 years. Settling down apparently marks the major psychological transition between BMH and MH. People had to learn to tolerate the presence of unrelated strangers, and not try to kill them on sight; some cultures today are still prone to do that! They could then engage in long-range trading.
Midway in the chapter I find the statement, "Specialization in roles may have occurred for the first time." I think not. Even in a kinship group of 50-150 persons, someone will be a little better than most at making tools, and another will be a little better than most at accurate throwing of weapons, or at climbing of trees. One woman's more nimble fingers might weave a better, stronger basket more quickly than others'. So intrafamily trading probably began way, way back. Once you are able to converse peaceably with people in the family nearby, interfamily trading can get rolling, and that will naturally grow into trade networks that span continents.
Looking through my notes, I find a number of interesting items about settlement and socialization. But I'll skip a few to get to the critical point. How much of all this has genetic underpinnings? The author thinks, quite a lot. We can see in our more slender skeletons, compared with "Cro-Magnon" of 10-12,000 years ago, that MH's have changed over that time. We aren't quite as likely to club one another over the head. It makes me wonder, how warlike were BMH's? The Dani in New Guinea and the Yanomami in Brazil, until the past few decades, were used to losses of around 30% of each generation to inter-village warfare. What was warfare like 40,000 years ago, when skulls were thicker and bones twice as robust (muscles also, one must presume)? Shudder!
But what is happening now? Human skin changed from pale to black after hair was lost from the body. [Just by the way, my personal notion is that hair loss had to soon follow the domestication of fire. Think of a furry month-old baby falling into the fire, or an ember blowing onto it. In my twenties I had a beard; it caught fire once, and only very quick thinking by my father kept me from suffering disfiguring burns (I still have a couple of tiny scars). I have read that the most popular theory for hair loss is running. Humans can run down anything except a thoroughbred horse; and maybe over a day or two, the horse would also get too tired to keep going. Perhaps both influences played a part.] The people that made their way from Africa to northern Europe and northern Asia became pale again. This seems to have happened primarily in the past 5,000 years. Europeans and north Asians have different genetic mechanisms for skin coloration, so paler skin evolved at least twice. Lactose tolerance evolved at least four times, at different times in different places. Our jaws are smaller than was average for earlier MH's, which is why so many of us have to have our wisdom teeth pulled. Suffice it to say, the sore back many of us wake up with is also evidence that 2-3 million years has not been enough for a truly functional and robust erect spine to finish evolving.
The author has numerous added examples. Physically we are still evolving, and those of our behaviors that have a strong genetic element are evolving also. Where will it all take us? The presence of five "races" (we need a better word now; this one is too political) indicates that the human species is partway along a path toward splitting into multiple species. If sea-spanning ships and jet planes had never been invented, in another 50,000 years, would there be three or four or five species of human? It's possible. If we plant a colony on (better, underground) Mars, how long will they remain the same species? Since there would be a much smaller number of them, genetic drift, along with a very few novel genetic alterations (mutations), could render them genetically incompatible with "the folks back home"; that is, a new species of human. Homo arensis?
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