Maybe human, maybe not

 kw: book reviews, nonfiction, anthropology, paleoanthropology, essays

We could wish more finds were like this. By far the most frequent discoveries by paleoanthropologists are of single teeth or parts of bones. Finding a half-jawbone with a few teeth attached is cause for newspaper headlines.

In natural history museums all over the world we see dinosaur skeletons galore (of course, each skeleton found in reasonably complete form is copied numerous times and sold to other museums). Yet only a handful of early human or Neanderthal or hominid/hominin skeletons have so far been found. Why? It is all about numbers.

Dinosaurs of many species were common all over the Earth for about 185 million years. Since the origin of hominins (pre-human apes and proto-humans), only a 4-6 million years have passed. Also, for much of that time, their numbers were few, in the thousands to a few hundred thousands, worldwide (mostly Africa and parts of Europe for most of that time). Thirdly, the number of species represented by the monikers "hominin", "hominid" and "early human" totals fewer than thirty, while there were hundreds of species of dinosaur, many of which existed in the millions and for millions of years.

To be blunt: lots more dinosaurs lived and died, compared to the record of human ancestry.

Given the rather small number of examples that exist, it is amazing that certain conclusions have been made about human ancestry. A few of the stories told by the old bones are relayed to us in Close Encounters with Humankind: A Paleoanthropologist Investigates Our Evolving Species by Sang-Hee Lee and Shin-Young Yoon (translated from Korean, translator not named). The 22 chapters began as columns written for a journal and a special issue.

A question often asked, "What was the first human ancestor after the split with apes?", led to Chapter 3, "Who were the first hominin ancestors?" By the way, it took me a while to learn the difference between hominins and hominids. To summarize online sources: "Hominids refer to all modern and extinct great apes, including humans, chimpanzees, gorillas, and orangutans, along with their ancestors. Hominins, on the other hand, specifically include modern humans and all our extinct ancestors that are more closely related to us than to chimpanzees." Thus, "hominin" strictly refers to an ancestor species to Homo sapiens, and "hominid" refers to all the "cousins" that are the great apes and their ancestors, back to the first great ape which split from the "all apes" common ancestor. On the Hominid Family Tree, the Hominins are a single branch leading to us. I hope that helps.

So, who were the first hominin ancestors? Six pages of discussion result in, "Probably either Australopithecus afarensis or A. amanensis." A. afarensis was "Lucy", whom you may have read about. More fossil discoveries and more study are needed to pin it down. Both these candidates lived between 3 and 4 million years ago.

An interesting coincidence is behind Chapter 8, "Is Granny an artist?" Two strains of discoveries come together in time. Firstly, evidence that woman began living long after menopause led to the Grandmother Hypothesis, that having grandmothers handy reduced the workload on young mothers, allowing them to have children more frequently. This is behind an early population boom. Secondly, the earliest instances of rock art are found in the same time period. It seems that such proto-writing/pictorial storytelling extended the lengthening memories of the grandmothers (and a smaller number of grandfathers; then as now, women usually outlived men, if they survived childbirth).

Another interesting intersection: upright walking came before brain enlargement. The changing vegetation of East Africa made it more favorable for apes that could see over the brush on the savanna. Spending more time upright made it easier to carry stuff (including babies) in the two hands that were no longer needed for locomotion. Why did babies need to be carried? Chimp and gorilla babies can cling to their mothers' fur. Humans don't have fur, and it is surmised that neither did hominins, after a certain point.

I have long had a certain idea about when and why humans lost their fur. Fire. There is a time mismatch that bothers me. Upright walking seems to have arisen between 4 and 7 million years ago, with fully modern striding-style walking appearing about 4 million years ago. However, the earliest evidence for controlled use of fire is just over one million years old. But it isn't known when "uncontrolled" use began. By definition, controlled use includes the ability to kindle a fire. Taking advantage of naturally occurring fires must have predated this by a lot.

Side note: the crazy old film Quest for Fire has "cave men" carefully tending a vessel holding burning coals, their only method of starting fires. In a battle with apish enemies it goes out, and one of them goes to find a burning fire he can "capture", but stumbles upon a group of people who know how to start a fire with friction. Other details are just eye candy. The racial overtones of that flick are astonishing.

Anyway, I have long thought it is likely that once proto-humans began spending lots of time around fires, being furry became a detriment and natural selection drove the species toward furlessness. Thus, the "naked ape."

The various chapters cover a wide, and very interesting!, range of subjects. A key element is the great increase in tools to investigate DNA relationships and the "molecular clock" (not all that clock-ish, it turns out) and newer analytical methods. Re-studying old bones, it turns out, yields new understanding. Old debates are resolved, and new debates arise.

The last chapter, #22, is "Are humans still evolving?" And of course, "Of course we are." Dr. Lee uses as an example the first thing I thought of upon seeing the chapter title: wisdom teeth. We are in the middle of losing them. More and more people are born without any. However, she brings up an interesting twist. In developed countries, better dental care is allowing people to live longer, who would have died early because of impacted or infected wisdom teeth. Perhaps this bit of natural selection has just been halted in its tracks, but only for a portion of humanity. Another example of ongoing evolution in humans is bad backs, and the gradual changes in the spine and posture. I hope later generations will be free of lumbar disk slippage and muscular ruptures in the lumbar area. It will take a while; humans and hominins before us have been upright for a few million years, and we are only partway through the process.

I could go on and on, but I hope instead that you will read this book and enjoy fascinating stories of what we know about the past few million years of human/hominin evolution, and how we know it.

More on continued human evolution

kw: book reviews, nonfiction, anthropology, paleoanthropology, evolution, human evolution

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:

1. Do the mechanisms of natural selection still operate on humans?
2. 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?

Yes, we are still evolving

kw: book reviews, nonfiction, anthropology, paleoanthropology, evolution, human evolution

The history of life is incredibly more complex than we ever thought. Just the history of this little cluster of twigs on the tree of life that we can call "humans, hominins, and their close kin" is incredibly complex. I truly enjoy reading essays by someone who knows these things deeply and tells us our stories with grace and wit. Close Encounters With Humankind: A Paleoanthropologist Investigates Our Evolving Species, by Sang-Hee Lee with Shin-Young Yoon, is just such a book. Dr. Lee is an anthropologist and department dean at U.C. Riverside. Mr. Yoon worked with her to prepare essays for the popular press in Korea and the U.S., and for this book.

One root question people have is this, "Are Neanderthals our ancestors, our cousins, or something else?" Simply put, they were "kissing cousins" when the species we call "modern humans" was being formed. Neanderthals are one of at least two ancestral species, and we are hybrids!

The book doesn't start there. The first chapter is titled, "Are We Cannibals?" I would put it this way: We cannot include human meat as a major part of our diet because that's too much like a perpetual motion machine. However, some human cultures have included small amounts of carnivory for primarily ritual purposes. Read the chapter for the gory details.

Dr. Lee doesn't sidestep controversies. Chapter 3 asks, "Who Were the first Human Ancestors?" We could thus ask which species represents the first Hominin. A Hominin (note the final "n") is a member of a species characterized by upright walking, a larger brain than a Hominid (note the "d") of similar size, and sophisticated tool use; probably also complex language. The Hominids are the great apes—Gorillas, Orangutans, Chimpanzees, Bonobos, Gibbons, and Humans—and all their ancestors back to the first great ape that split from the lesser apes and monkeys. The recognized Hominin genera are Homo, Australopithecus, Ardipithecus, and Paranthropus. Species in the genus Homo are H. sapiens (ourselves), H. neanderthalensis, H. habilis ("handy man"), possibly H. rudolfensis, and H. erectus. Homo erectus, "upright man" is probably the first, but various scientists argue for other possibilities, and the chief ones are discussed in this chapter.

Along the way to tracking down our Neanderthal (and other) roots, matters are discussed such as the incredibly painful birth experience, because of a combination of large brains in newborns and narrow hips due to upright walking (waddling is wasteful of energy); when different skin colors arose (I was surprised to find it was primarily 5,000 years ago); the biggest of the apes, the half-ton Gigantopithecus; and why we still have sore backs.

Once we get to the time period from 100,000 to 40,000 years ago, we find that our twig of the tree of life is actually braided, or networked. Perhaps half a million years ago some people left Africa for Europe and Asia. At present it seems two groups followed similar but distinct evolutionary tracks to become the Neanderthals in the west and Denisovans in the east. Later, some time before 70,000 years ago, another group left Africa. They are called by various names; the most neutral is "early modern humans" or EMH. They are considered early members of H. sapiens, and they must have had better teamwork and better tools, and perhaps a different breeding schedule with close spacing of offspring, because they multiplied until they outnumbered their cousins who already lived there.

Now that a genetic sequence has been produced for both Neanderthals and Denisovans, it is clear that they interbred with the EMH people. Whether the N's and the D's were wiped out or subsumed into the larger group is not known. What is known is that European DNA includes about 4% Neanderthal DNA and a lesser amount of Denisovan DNA, while for Asians it is the reverse, and Australians may have 6% Denisovan DNA.

At this point I wonder, was there perhaps yet another species out there, not yet discovered, that contributed to the modern gene pool? And I find another matter even more interesting: All three of these types of humans were more robust, and had a little larger brains (5%-8%) than modern humans. We don't know enough about the Denisovans to be sure how strong they were. An average Neanderthal was twice as strong as an EMH, and the average EMH was at least twice as strong as modern humans.

Not all of that is because so many of us have sedentary lifestyles (Most people living outside the West have more active lives). I live near a large population of Amish. They work hard and are all very strong. A typical EMH would be even stronger. They were genetically prepared to become stronger.

The last chapter asks, "Are Humans Still Evolving?". The answer is, "Of course!" Just because we invented culture and science and technology with all their conveniences, doesn't mean there are still no selective pressures for natural selection to work on. Remember, 2/3 of the world has only a fraction of the conveniences and medical infrastructure that an American or European would consider normal. I certainly hope that we are evolving toward having less lower back pain! But considering that it has been with us for about two million years, I suppose it will be a good while yet. I point out wisdom teeth, and our shrinking jawbones, as evidence of continuing evolution. Dr. Lee thinks we have removed that matter from selective pressure because of low-cost dental surgery. However, there are still large numbers (the 2/3 mentioned above) who have little or no dental care, but whose jaws are also shrinking as food sources change. In whatever measure infected impacted wisdom teeth reduce reproductive potential, there will be benefit to having a mutation that reduces or eliminates them.

There is reason to believe that the great increase in human population that followed the agricultural revolution about 10,000 years ago has led to an increased rate of evolution among us. This is just touched on in this book, but we are referred to another, The 10,000 Year Explosion, by Gregory Cochran and Henry Harpending. I got a copy right away. Stay tuned!

This review just skates on the surface of Dr. Lee's offerings. What a joy to read!

When did human evolution stop?

kw: book reviews, nonfiction, paleoanthropology, archaeology, historical linguistics, primatology, social anthropology, evolutionary psychology, population genetics, human origins, natural selection

The simple answer to this post's title: It hasn't. Among those who accept evolution of the human animal, it is common to think that we've reached some kind of pinnacle, and no evolutionary change has taken place in the last ten or twenty thousand—or perhaps 100,000—years (For those who don't, of course no evolution has ever taken place). The book Before the Dawn: Recovering the Lost History of Our Ancestors by Nicholas Wade presents a synthesis of what is known and strongly inferred in the disciplines related to human origins. The picture is full of surprises.

Item: When did people begin to wear clothing? Fabrics are so rarely retained in "fossil" deposits, we can't begin to guess. Body lice provide the answer (yuck!). Head lice, equivalent to head-and-body lice in apes, live in the hair. Body lice live only in clothing, and move to the skin to feed, but lay eggs in clothing, because there is too little hair on most human bodies to reliably protect the nits. So when did body lice evolve? Genetic dating from modern head and body louse populations provides the surprising answer: about 70,000 years ago. Such dates currently suffer from large uncertainties, so the actual development of the body louse, shortly (a few thousand years) after clothing became common, occurred before 40,000 years ago, and most likely 80,000 or later.

Item: When did proto-humans lose their body hair? Both chimps and bonobos (once called "pygmy chimps") both have fair skin under that black hair. Only the face, hands and feet are dark, because of a permanent tan. Dark skin over the body probably arose as hair was lost, to protect the skin from the sun. "Black" Africans can be sunburned, but it takes a lot more sun exposure compared to lighter-skinned people. When did darker skin over the whole body evolve? Genetic dating again provides an answer, this time from the genes that produce skin pigments: about 1,200,000 years ago.

Strangely, I looked for information on the "first use of fire", but Wade doesn't mention it. A BBC News article of 22 March 2004 states that early African humans, possibly Homo erectus, seem to have had hearths as early as 1.5 million years ago. Another article, dated 29 April 2004, about H. erectus in Israel, has them using fire in sophisticated ways 790,000 years ago. It seems to me that nakedness arose primarily as a result of fire use. Other explanations, such as sexual selection, seem less compelling.

What is interesting, though, is the million or more years that passed between the loss of hair and the development of clothing. Production of textiles must require a change in thinking that didn't occur earlier. The Acheulian "toolkit" was used by at least three species of Homo from 1.7 million years ago until it was supplanted 250,000 years ago by Mousterian (H. Neanderthalensis in Europe) and Middle Paleolithic (H. Ergaster in Africa) technologies. These related technologies show two things: that there was contact between African and European species of Homo; and that one had attained sufficient brain power to greatly improve their use of stone tools, which the other quickly adopted (it takes less wit to copy than to invent). So, apparently, clothing other than cured skins was an invention later yet.

I've known the term "anatomically modern human" (AMH) for decades. I confess that I didn't think about it much. But later, the term "behaviorally modern human" (BMH) gave me pause. Is there a difference? Sure is, by tens of thousands of years. It seems AMH's, which arose in Africa 100,000 years ago, could pass for human today, as long as they didn't do anything. But they didn't live like BMH's, who lived like the hunter-gatherer groups of today, such as certain "primitive" tribes in South America or New Guinea. Evidence of BMH living appears just after 50,000 years ago in Africa, and about 45,000 years ago in Europe.

AMH living was by foraging and minor hunting. Family groups stayed together, in bands of related families that scattered and coalesced on a daily basis, numbering 50 or fewer. Few activities other than food gathering and preparation, procreation, and sleeping, occurred.

BMH living included much more hunting, of larger game, and specialized plant gathering. A great increase in the use of ornaments and artful trinkets arose. The stone toolkit, called Upper Paleolithic, was much more complex, with specific tools for specific uses, and complex tools made of bone, antler, and ivory. Musical instruments, such as bone flutes, are found for the first time in BMH leavings. The people ritualized burial. And they traded among groups, much more than AMH's, to obtain materials and products found far from their home ranges.

Add one item: About 50,000 years ago, BMH's from the "ancestral human population" (AHP) in Africa migrated beyond Africa, apparently for the first time since 1.8 million years ago, and established themselves eastward and northwestward to the limits of the Eurasian continent in a few thousand years. They seem to have supplanted and replaced Neandertals in Europe and "archaic Homo" people in Asia, in less than ten thousand years. During this time, some reached Australia, something the archaics didn't do.

When I saw all these together, I was convinced for the first time that the "multiregional" hypothesis, which requires persistent gene flow among the African, European, and Asian species of Homo, must be wrong. What was it that kept Africans from continuing to migrate to Eurasia, at least successfully, between 1.8 million and 50 thousand years ago? The most likely answer is that the land was occupied by Neandertals and archaics, who either drove out or destroyed invaders. In the same way, the AHP in Africa filled at least the Northeast part of that continent and kept the other species from invading.

Once the AHP developed BMH living, they could make better use of resources, had better weapons, and could stay together in larger groups, compared to the other species, and could successfully invade Eurasia. However, even with these advantages, it wasn't a simple walkover. The number of BMH's who became the ancestors of all non-African people was less than 500, and possibly as few as 150.

OK, so what happened since 50,000 years ago? Are we BMH's who have somehow adapted to settled life? Are today's remaining hunter-gatherer (H/G) groups BMH's? Not really. Although BMH's were anatomically very nearly the same as AMH's, there are differences between today's people, both in Africa and Eurasia, and the people of the African AHP. If you were to take a range of modern people, of all races, of various sizes and ages, and pair them up with AHP folks of similar size and age, you'd find the earlier people had thicker skulls and heavier bones at all ages. They were not as heavily built as Neandertals, but were definitely more like American Football players than like Soccer (European Football) players. The AHP's also stayed in smaller groups than members of modern H/G groups do.

The main reason is inter-group combat. There has been a strong tendency among anthropologists to understate the level of aggressiveness and prevalence of warfare among "innocent savages." An unbiased look at the record reveals that the greatest single danger to humans through all ages was and is other humans. Xenophobia is the natural state of the H/G mind, the BMH mind, and the AMH mind, as it was for all earlier species of Homo.

It is now known that groups of chimps engage in wars of extermination against neighboring groups, and that the leading cause of death among males is "chimpicide". Bonobos, with a female-dominated society, do not engage in such warfare...a good reason for turning over all politics to women!

The greatest single cause of both male and female death in most H/G groups is warfare and killing raids between groups. So, while trade arose at least 50,000 years ago, it probably occurred primarily among groups that couldn't exterminate one another, just as it does today among all the mutually warring tribes in New Guinea and South America, for example. "You aren't my brother or cousin, but unless I judge I can destroy you, I'll call you friend...for a while."

My father's cousin, while a missionary in New Guinea in the 1950s, saw frequent warfare and some cannibalism. Two groups of men might trade one day, and slaughter one another the next. A smaller village might have all its men killed, whereupon all their children would be killed, plus most of the women, and the rest taken as concubines.

Let's look at a few numbers. About a third of adult male chimps die in combat. The number is the same among the Yanomamo, a Brazilian tribe of H/G's. One study showed that a typical tribal society lost, on average, 0.5% of its population yearly to warfare (that's ~1% if the men and a smaller proportion of women; and among men, that's a 26% loss per thirty years). However, averages tend to hide incidents. Most inter-tribe warfare is carried out by small battles and raids a few times per year, or perhaps monthly. Pitched battles are much less frequent, but cause huge carnage: A 30% loss on both sides is typical. Modern societies prior to 1900 AD could produce similar death tolls: At the battle of Gettysburg, the Union side lost 21%, and the Confederates lost 30%.

However, the two World Wars of the 20th Century resulted in losses of less than 10% among the soldiery, and a percent or less of the engaged nations' total citizenry. Stalin's purges of the 1940s and '50s were actually worse than either World War in terms of pure carnage...they were wars of another sort. But in 2002, though a number of wars were in progress around the globe, including America's war in Afghanistan, 0.3% of deaths were due to warfare.

But these latter figures are comparing recent wars among settled societies, with wars among H/G societies, BMH societies...and apes! They are probably not entirely fair. Wade doesn't go into this, but by my own study, I find the following: History is full of war stories, from Troy to Sparta to Carthage and so on. But it seems the total toll of warfare among settled societies is typically about half that among H/G societies.

I wonder what is cause and what is effect? Did settlement and agriculture result in a preference for negotiation? Or did the development of more negotiation-prone people—perhaps first among those who profited most from trading—allow settlement to occur?

I'd say it is a coevolutionary change. Our skeletons reflect the fact that we have less reason to fear being bonked on the head some random night, compared to the AHP, and less need for face-to-face combat. Although today's H/G members live very similarly to the AHP, a Yanomamo or Dani person can be socialized to live in a city. I suspect a person brought in a time machine from 40,000 years ago would be unsocializable, or only partly so.

The brain has changed since that time. So far, two genetic changes that determine brain size, and probably size in specific areas, have been found and genetically dated. One occurred 37,000 years ago, the other 6,000 years ago. The people of 50,000 years ago were, from archaeological evidence, able to live in larger groups than earlier peoples. They were able to extend the idea of "kin" to a larger group than before. But each change to the brain seems to have increased the number of "others" a person could tolerate.

By 15,000 years ago, when settlement began, it seems people could tolerate even greater numbers, and additionally, accept direction from leaders. Both are required for a few hundred people to live in continuous close proximity. It seems strange that these first settlements were not primarily agricultural. They seem instead to have been "places to be" between hunting and collecting expeditions, and trade centers. Specialized skills proliferated; the best hunters got their spear and arrow points from the best stoneworkers, as the best clothing makers got needles and other tools from bone workers...and in turn traded clothing to those less skilled.

The later development of agriculture led to much larger settlements, about the time of the 6,000-year-ago bump in brain size. A larger brain adapts one to the need to remember a larger number of people. It was not much later than this that lactose tolerance evolved among those who kept herds of large mammals. To this day, lactose tolerance or intolerance indicates whether your ancestors were farmers or ranchers.

Now think, today an office worker can step out of an apartment and essentially vanish into a city of millions of strangers, and return safely hours later! Rather extraordinary, wouldn't you say?

What other genetic changes have arisen recently? Malaria resistance among those living in subtropical areas has evolved at least twice since 10,000 years ago (one such change causes sickle-cell disease). Our sense of smell is much reduced compared to just 15,000 years ago, because most of the olfactory gene set has become inactive. Whether this is because of the stench of early cities, of because of less need to smell out game, I forbear to speculate!

The changes to brain and body that occurred prior to 50,000 years ago are found in all humans. Those that arose later are found in larger or smaller numbers depending on where a mutation arose and how strong a benefit it ensured.

This leads us to the most visible differences among human populations, those that correlate best with the continent one's ancestors inhabited: we call them races. While skin color is often considered to be the main indicator of race, it is not really the best. The Caucasians in southern India are darker than some Africans; some Japanese (and I don't mean Ainu, which are very pale) are paler than most Caucasians; many Australians (aboriginals not Austro-Brits) are darker than most Africans or Indians. If you take almost anyone, and paint their skin white (or any solid color of your choice), most people can tell at a glance what continental type they typify, and often the subtype (pygmies and Inuit are quite distinctive, for example).

Regardless how extensive "racial" differences are, it seems they arose no more than 12,000 years ago. They reflect, as do many other indicators, that most people in history seldom moved far from the place they were born. The subtypes within continental groups emphasize this. So, rather than the "not politically correct" attitude toward any mention of racial genetics, it would be better to look upon the diversity of human types as a library of the history of humanity.

One thing is sure: We continue to evolve. We are more gracile than the AHP. Gracility may continue, but it has probably already reached it logical limit among East Asians. Even though Chinese fed a "Western" diet grow taller than their parents, they remain on average much slenderer than Europeans. The continually increasing complexity of modern life will, unless civilization collapses, lead to people with larger brains and more multitasking skills, first behaviorally, and over a few generations, genetically. We won't become the bare brains of science fiction, but we may become smaller, thinner, quicker, and less aggressive in the future. Should Homo sapiens survive another 50,000 years, no doubt our descendants will look back at us as quizzically as we look back at the people in Africa, 50,000 years ago, some of whom managed to escape that continent to colonize the rest of the planet.