A Brief Account of our Lineage

This book is mostly about the process that transformed a bunch of boring flint-chippers into the most interesting species on the planet—on our way to the stars, if we don't blow ourselves up first. Our time frame is mostly the last 50,000 or so years, starting with the expansion and diaspora of modern humans out of Africa. But still we must set the stage, name the players, provide some background. Here we give a quick overview of the first six million years of human evolution.

We begin with the common ancestor of chimpanzees and humans, some 6 million years ago—sometimes called "chumans" in the genetics literature. That date of six million years is a reasonable guess based on the fossil record, but since the earliest candidates for human ancestry, early versions of bipedal African apes called Australopithecines, could plausibly also be chimp ancestors, dates as recent as 4.5 million years or as old as 7.5 million are still on the table. We can't get much more precision from DNA evidence, since the relevant mutation rates are not very well known.

We have not found chuman fossils, but we have quite a bit of fossil evidence from early hominids not long after (or before?) the split. That fossil absence is nothing mysterious, by the way: conditions for fossilization are usually poor in central Africa, due to moisture and acidic forest soils, particularly west of the Rift valley. There's also far less uplift and erosion in that area, so the fossils that do exist tend to stay buried and invisible. We have almost no fossils of chimpanzees, which are fairly common today. Judging by their high level of DNA diversity, they have always been common. As we write there are a total of 3 teeth in the known fossil record of chimpanzees.

Considering genetic information and the shared characteristics of chimpanzees and early hominids, as well as characteristics shared among more distant relatives such as gorillas, we have a partial picture of chumans.

We think that they were a good deal more like chimpanzees than humans. Chumans were probably about the size of modern chimpanzees. They were climbers, spending considerable time in the trees. When on the ground, they walked on all fours, putting weight on their knuckles. This awkward style of locomotion (called knuckle-walking) is also seen in gorillas and some other mammals that use their hands for purposes other than walking such as climbing or handling food. Since chimpanzees have arms that are longer than their legs, they're able to knuckle-walk without looking completely ridiculous.

Their brains were about a third the size of ours today, like those of chimpanzees. That hardly means that their brains were unusually small. In fact, relative to body size, their brains were among the largest of all mammals, exceeded only by later hominids such as ourselves. Dolphins are the only competition.

They probably made and used extremely simple tools, just as chimpanzees and gorillas do today, but those tools weren't crucial to their survival, and were either perishable, such as twigs or grass stalks used to extract termites, or so crude that we can't distinguish them from random rocks. The geological record makes that clear through the things we don't see. While fossilization of skeletons is rare, stone tools last. Each toolmaker makes many over a lifetime, and so we find many, many stone tools for every toolmaker skeleton. We find no recognizable stone tools that date back to chumans. This almost certainly means that chumans didn't make any.

Their social organization may have been like that of chimpanzees, with separate male and female hierarchies and no pair bonding, but we don't really know. Fierce competition between males (over females, what else?) commonly leads to sex differences in size, while the sexes are about the same size in monogamous species. Judging from the fossil evidence, early hominid males seem to have been almost 50% bigger than females, which implies that our remote ancestors were far from monogamous. However, that tells us what chumans weren't, not what they were. Gorillas and orangutans are both sexually dimorphic—both adult male gorillas and orangs weigh about twice as much as adult females—and non-monogamous, but their societies are very different from each other and from that of chimpanzees.

Chumans likely shared an unusual behavior that we see today in both chimpanzees and modern humans—war. Male chimpanzees from one troop form groups that repeatedly attack chimpanzees in neighboring groups, even to the point of exterminating their rivals in a pattern very reminiscent of primitive human warfare. There is reason to believe that such organized aggression has existed throughout hominid evolution. In particular, many hominid skeletons appear to have been butchered.

They had no speech, any more than chimpanzees do today. Chumans had not yet acquired key human traits: they didn't walk upright, have speech, or use tools.

For unknown reasons, populations of chumans separated and began evolving along different paths. It may be that the shrinkage of forests east of the Rift played a role in this. The first importance differences in the line that that led to humans were bipedalism and smaller canine teeth, first seen in hominid skeletons from about 3.8 million years ago. These early hominids are called Australopithecines ('southern apes'). In the past Australopithecus was used as the name of a genus that encompassed all these, but in the last decade the fashion in naming fossils seems to have changed, splitting (as opposed to lumping) is on the ascendant, and new named genera are proliferating like Ardipithecus, Sahelanthropus, or Ororrin.

Bipedalism, walking upright on two legs, is plausibly related to a move out of the trees, and it was eventually important in freeing hands for tool use. However, the evolution of bipedalism had to be driven by advantages that existed at that time, not ones that would show up in the far future. We don't know which benefits drove the evolution of bipedalism. There's a lot of reasonable speculation about the advantages of standing on your own two feet, such as freeing up hands for carrying food and/or babies, reducing exposure to solar radiation, or more efficient running. But no explanation has been generally accepted.

We know a little more about the forces driving dental changes. Large canines in chimpanzees are used for threats and fighting, especially in males. They are also used for opening tough foods. A move towards smaller canines suggests to some reduced competition between males, perhaps due to a change in social organization. Others see in canine loss an indication of a change in diet, perhaps to one that includes more seeds and small berries that require a lot of side to side chewing. Thicker enamel, on the other hand, is consistent with a more varied diet, one that included roots and tubers more than fruits and leaves. At this point, though, brain size has not increased and there are still no recognizable tools. Australopithecines may have walked like men, but in most respects they were still very much like apes.

The first recognizable tools show up about 2.6 million years ago while Australopithecines first appear long before, approximately six million years ago. Theses tools were sharp flakes chipped from pebbles, likely used to cut through hide and tendons and extract meat from carcasses. The cores from which the flakes are struck may have been used as tools also, but as is so often the case, we don't know. These tools are crude: they are identifiable partly by the way that they cluster and show up out of geological context. This tool tradition (the Oldowan industry) continued for another million years or so almost everywhere, and it persisted until very recently in much of Asia. This amazing technological stasis is characteristic of early humans, and we'll be noting it again. The tools were used to prepare meat from animals such as pigs, antelopes and zebras, but it's not clear whether they obtained these animals by hunting or scavenging.

The hominid fossils of this era are few and confusing: some show moderate brain expansion, others show tooth and jaw reduction—both of which trend toward modernity—but none show both. It is not clear which types or types of hominid made these Oldowan tools. Some argue that there were several co-existing hominid species in these times. We're sure that one contained our ancestors, but that's about all we're sure of. These early humans had, through tool use, managed to become successful scavengers and (perhaps) predators without evolving the characteristic suite of predator adaptations such as claws and fangs. This innovation changed the selective pressures; in a sense, humans began to create their own environment and drive their own evolution, a trend that would intensify over time. The famous Homo habilis, regarded by many as simply another Australopithecine with a slightly larger brain, is a leading candidate for having made the tools, but in the current fashion of splitting even this taxon has been split so that some of them are now called Homo rudolfensis.

Although we understand that naming a new species is one of the more harmless ways of writing one's initials in the snows of time, we think that such efforts (going overboard on splitting fossils into different species) are intellectually sterile. By the least incoherent definition of the word, two populations are separate 'species' if members of population can't (or for some reason don't) have fertile offspring. Of course no one knows whether this was the case for ancient hominids whose skeletons look different and who were contemporaries. As for determining whether one species of hominid has, over time, turned into another (a chronospecies), who could possibly know? We do know of pairs of mammalian species that split several million years ago but can still have fertile offspring (for example, red deer and axis deer are still fully interfertile after 6.8 million years of divergence) and we also know that testing the classification of any chronospecies would require time travel. In practice, when paleoanthropologists talk about hominid species, they're saying that some of the skeletons they find look significantly different from others, and that's all that they're saying.

Shortly (!) afterwards, around 1.8 million years ago, we begin to find skeletons that look much more familiar - Homo erectus. They were larger than previous hominids, and had bigger brains, around 900 cubic centimeters in volume (moderns average about 1350 ccs).

Below the neck, they looked a lot like us, with long legs and a barrel chest, in contrast to the cone-shaped torso of the apes. The cone shape of the apes accommodates a large gut reflecting a high volume diet of relatively low quality items like leaves. Homo erectus suddenly has a thorax with parallel sides, like ours, suggesting a major change to a higher quality diet. There are two principal candidates for just what this shift in diet could have been: the “guy theory” is that they were the first active hunters in our ancestry and that the amount of meat increased drastically at about this time. The competing “girl theory” is that they mastered fire and took to cooking wild vegetables, especially tubers since there is a lot of edible biomass in tubers everywhere and much of it is not exploited by other species. Fire and cooking would have broken down the complex, nearly indigestible starches in tubers and other gathered plant foods, rendering high-volume digestive tracts unnecessary. We refer to these as “guy” and “girl” theories since the ecological novelty reflected the activity of males in the former, since males everywhere hunt more than females today in our species. In the latter the ecological novelty reflected the likely female activity of gathering. Recall though that while the attribution of hunting to males and gathering to females does reflect a near human universal, argument by analogy is not very convincing. In social predators like the felids and canids there is no such specialization and females are as good or better than males at hunting.

Above the neck, Homo erectus looked less human. Their skulls were long and low and had thick walls. The face was significantly different from that of modern humans, with a flat receding forehead and no chin. The sexes differ in size by about the same amount as living people, suggesting that social organization definitely differed from that of chumans, with less intense competition between males. On the other hand the skulls of these creatures were extremely thick and rugged, as if the function of a helmet was being incorporated into the bones themselves.

Homo erectus made tools, tools that were more sophisticated than those of the previous Oldowan tradition, but only in part of their domain. This new tool tradition, the Acheulean, is characterized by hand axes, large teardrop-shaped stones bounded with sharp edges. We call them hand axes, but their actual function isn't clear. Their main use may still have been as a source for sharp flakes. Although these new tools are more sophisticated than before and brains are larger, erectus did not have the capacity for innovation we expect from modern humans. The Acheulean was a real tradition in the sense that handaxes are distinctive. On the other hand, they seem, insofar as anyone can see today, to be both dangerous and useless. Nevertheless the tradition persisted unchanged for a million years or more and was essentially the same from Capetown to London to Delhi. But the Acheulean only occurred in part of the range of H. erectus: in China and Southeast Asia the Acheulean never penetrated. The division between the Acheulean and the old-fashioned Oldowan chopper-chopping tool tradition is called the Movius line after its discoverer. While Homo erectus on either side of the line looked much the same, they must have been different species, since any cultural transmission at all across the line would have spread handaxes to the East. We suspect that tool-making in these early humans was more hard-wired and less a product of true learning than it is in humans today. Bird song may be the right analogy.

While this division of the world of Homo erectus into Acheulean and Oldowan has been known for decades, more recently some archaeologists have seen a third group of somewhat different crude tool traditions, called simply “Mode I”, north of the Acheulean range. (The nomenclature here is confusing: conventionally Mode I refers to crude tools like those of the Oldowan, Mode II to the Acheulean hand-axe tradition, and Mode III to prepared core techniques. The new version of Eurasia at this time splits Mode I into Oldowan and Mode I proper. Or something like that.) The simplest explanation of the pattern is that the earliest erectus to leave Africa were bearers of a simpler technology, a precursor to both Mode I and Chopper-Chopping tools, and that the Acheulean evolved slightly later and expanded in their footsteps, failing however to reach the ends of H. erectus lands.

A classical interpretation of this pattern is that the Acheulean is evidence of some new cognitive leap and that this leap did not occur in the Chopper-chopping tool and Mode I lands. These latter do not really deserve to be called "traditions" since, without charity, they are crudely banged up rocks. Acheulean hand-axes on the other hand are built to a common pattern and it is a pattern that is difficult to carry out. The next clear technological innovation to appear, Mode III, is the use of prepared cores. This Levallois technique involves preparing a core; that is, a piece of rock shaped very carefully so that at the end a blade is removed with engineered properties. This technique shows up later, on the order of a half million years ago, and it is found in essentially the same areas where the Acheulean was found. The second wave of innovation did not penetrate the Mode I fringes.

This proposed tripartite division of the world of H. erectus is eerily reminiscent of the way that linguists divide old world languages into those that are agglutinative, inflective, and isolating: isolating languages closely map to the old Chopper-chopping tool world, inflective languages to the Acheulean, and agglutinative languages to the Mode I blade tradition. This is the basis of the Paleolithic Continuity theory of human language diversity. This theory states that human languages and the great divisions between them are ancient, at least as old as the middle Paleolithic. This idea is not in fashion in North America but it is not entirely implausible and is worth noting (Alinei 1997).

About half a million years ago, a new variant (or successor to) of erectus appeared in Africa and spread to Europe. This species is named Homo heidelbergensis after a characteristic skull found near Heidelberg, Germany. Homo heidelbergensis retained many of the premodern features seen in Homo erectus, but they had significantly larger brains. Their cranial capacity was around 1200 cubic centimeters, as large as that of some people today. They seem to have been the first to permanently colonize Europe, which wasn't so easy in the Ice Age. Homo heidelbergensis is thought today to be the common ancestor of both Neanderthals and modern humans. These latter two species, the extinct Neanderthals of Europe and Western Asia and modern humans, ourselves, are subjects of subsequent chapters.


Big Events in Human Evolution


The preceding section provides a sort of timeline of human evolution over the last few million years. Many of the important events and changes in our evolution can't be put in this timeline since we have no idea when they happened. In this section we describe some of the most important changes in our history. When we know something about when they occurred we will cross-reference the timeline.

Upright bipedalism - Walking on two feet, happened early on. Early Australopithecines walked upright on the ground even while they retained slightly curved finger bones indicating a facility for moving around in trees. This, along with canine reduction, is the earliest anatomical change we can recognize. There are numerous plausible theories about why our particular lineage took to upright bipedalism but none of them are solidly established. One, for example, is that the total incident solar radiation on an upright walker is less than that on a quadruped, so bipedalism may be an adaptation to diurnal movement in open country. Another is that upright bipeds are more efficient runners {Bramble Dennis M. and Lieberman Daniel E., 2004, Nature, 432, 345-352}. We also like Clifford Jolly's {Jolly Clifford J., 1970, Man, 5, 5-26} idea that seed eating may have favored bipedalism. His idea is that the rate of caloric intake of large packages of food is limited by chewing ability, while intake of small packages like grass seeds may be limited by the rate at which the hands deliver them to the mouth. Bipedalism, leaving the hands free, could have been strongly favored if much of the diet were small objects like seeds and berries.

Canine reduction - We have lost the protruding canine teeth (fangs) that monkeys, apes, and many other mammals have. While our canine roots are still prominent, like keystones of our dental arches, the teeth themselves are small and act like premolars. This reduction is apparent in very early Australopithecines of three to four million years ago. In the 1970s there were two prominent theories about canine loss. The first, perhaps inevitable in the age of beads and bell bottoms, was that males became mellow, gentle, and helping so this instrument of aggression and fighting was no longer necessary nor useful. The second is that tool use made the canine redundant for opening tough foods. Neither theory is very satisfactory: there is no indication that males then or now became mellow, and the first stone tools don't appear until a million years or so after the loss of the protruding canine.

Home base and the division of labor - In most old world primates the two sexes obtain and eat much the same things although there are occasional specializations like hunting among male chimpanzees. Low technology humans, on the other hand, universally have a division of labor in which males and females forage for different foods. They then return to a home base, a camp, and exchange these foods. The usual case is that men hunt and women gather vegetables, fruits, and other small package items. The home base means that infants, other dependents, and elderly can be left in an agreed-upon location and provisioned when adults return at the end of the day. This is not so different from what denning predators like cape dogs do.

Tool use - An older view is that tool making and tool use were prime drivers of human evolution. This idea has been tempered in the last few decades by the finding that apes use termite sticks as tools and some birds even use thorns in a similar way. It has also become clear that our ancestors were upright bipeds with reduced canines long before stone tools appear in the archaeological record about two and one half million years ago.

Fire - The earliest unambiguous hearths are less than one half million years old but control of fire may be much older. Fire would have made many more foodstuffs available to our ancestors, for example by breaking down complex indigestible starches. Unfortunately casual use of controlled fire would not leave an unambiguous archaeological signature. There are ash layers in many older sites but these could as easily be the results of natural fires.

Hunting - The role of active hunting, as opposed to scavenging, in human evolution has been the subject of dispute for years. Raymond Dart, the discoverer of the first Australopithecine fossil, had an elaborate theory of their "osteodontokeratic" (bone, teeth, and horn) technology that was used in active predation of other large mammals. This theory did last for long, but much dispute remains about the importance of hunting from several million years ago until the arrival of modern humans forty thousand or so years ago. The geographic expansion of Homo erectus from Africa almost certainly reflected a new improved diet, especially in view of their new thoracic morphology that indicates a big reduction in gut volume. The two candidate explanations for this are that they started active hunting and they were exploiting a new plant food like tubers. There is little or no evidence that they were active hunters, and the tuber model requires control of fire for which, again, there is no evidence. Since they entered some fairly cold seasonal environments it is hard to imagine that they were not hunting since plant food would often have been scarce. It is also hard to imagine that they did not control fire since it often was very cold.

Loss of estrus - Mammalian females share fundamental features of reproductive cycling. In the first part of the cycle the ovary introduces estrogens in the circulation. These hormones cause growth of the uterine lining and after some time lead to the release of luteinizing hormone from the pituitary gland (the LH surge). This in turn induces release of eggs from the ovary that move toward the uterus and are, if all goes well, fertilized by sperm present in the ducts. Meanwhile the scars on the ovary where the eggs were released produce another steroid hormone, progesterone, that causes even more development of the uterine wall in preparation for implantation. If implantation does occur a “messenger” from the fertilized egg, chorionic gonadotrophin, tells the mother to keep producing progesterone to maintain the right environment in the uterine wall. If there is no implantation, ovarian production of both estrogens and progestins declines and the rich uterine lining is resorbed by the female. In many mammals this cycle is driven by season, occasionally by the presence or absence of a male or males, while in others like humans it is regular.


In most mammals the estrogens released during the first half of the cycle affect the brain of the female causing her to become sexually receptive (agreeable) and proceptive (actively seeking). Anyone who has had a dog or cat in estrus or “heat” is familiar with these effects of estrogens. They also affect cells in the lining of the vagina leading to the production of odors called pheromones. These odors have a strong effect on males. Again owner of a cat in heat are familiar with a yard full of snarling tomcats, all drawn by the powerful odor. After ovulation, estrogen production picks up again during the second half of the cycle but the simultaneous production of progesterone blocks the effects of estrogens on the libido of the female.

Humans have apparently lost this whole mechanism: human female libido is not dependent on estrogens and is not impaired by progesterone. If the human vaginal epithelium produces pheromones, human males do not detect them. Humans are sexually active throughout the cycle but we are not so unique in this: some of our relatives like gibbons or bonobos are libidinous like we are. Human female libido is instead dependent on male sex steroids, androgens, rather than on estrogens. For this reason libido persists though human menopause. There is no good evidence about when this fundamental change in our reproductive system occurred.

Menopause - Along with a few toothed whales human females experience menopause in which sexual cycling ceases and fertility is terminated. Menopause is a puzzle in anthropology since fertility is terminated among females with years of productive vigor ahead of them. How could this evolve? The best current hypothesis involves grandmothering: the idea is that females do more toward the propagation of their genetic material by ceasing to reproduce and investing instead in grandchildren. There is substantial ethnographic support for this hypothesis in that grandmothers among contemporary foraging people work very hard indeed helping their daughters and the children of their daughters.

Menopause occurs when the ovary becomes depleted of cells that would become eggs, around age 50 in all human populations. The rate of depletion of eggs over time in humans and chimpanzees is roughly the same but at age 45 chimp females are senile and ordinarily dead. Kristen Hawkes (2003) at the University of Utah suspects that the critical event in our evolution here is not so much the appearance of menopause but a prolongation of the human life span, probably driven by the fitness benefits of grandmothering. Menopause under this model is an incidental byproduct of our longer lifespan. Again we have almost no solid data about the time that these events occurred in our past: they could have been quite recent. Recent research by Rachel Caspari of the University of Michigan and colleagues suggests that Neanderthals, a cousin of our own species that occupied Europe and parts of Asia from 150,00 or so years ago until about 35,000 years ago, did not enjoy the long lifespan of modern humans (Caspari and Lee, 2004).

Another argument for the relative newness of menopause is that it is sloppily engineered. The ovary ceases to function. The brain and pituitary system that worked with the ovary to maintain the menstrual cycle does not “realize” that the ovary has quit, and continues to try to get the cycle back in shape, releasing for example high levels of luteinizing hormone and follicle stimulating hormone. The mechanism may then be as simple as follicle depletion of the ovary with no or few other genetic changes working with the newly revised set of reproductive timings.

There is another evolutionary force that is probably an important part of this puzzle: reproduction at older ages by males. In many species male-male competition is strong and pervasive such that older males are usually defeated and forced out of the group. Blatant face-to-face violent competition within groups is rare in humans and older males can reproduce at older ages, especially in societies where older males command resources. Reproduction at older and older ages can select for longevity in a species, and such selection could have extended the human lifespan a lot, including the lifespan of females as a by-product of selection for longer male lifespans (Tuljapurkar et al., 2007). If this happened and the reproductive system did not keep pace with the new lifespan then something like menopause would be at least facilitated.

Groups of pair bonds - Some primates form durable mating male-female pairs, but the only ape to do so is the gibbon. Other arrangements like harems or troops are more common both among larger primates and among mammals in general.

In a harem there is one reproducing adult of one sex and more than one of the other sex. Gorillas and hamadryas baboons are mostly organized into one-male harems. African Cape Dogs live in one-female harems with a number of males that are related to each other. Troops contain adult reproductive individuals of both sexes, among whom there may be complex competitive games and strategies to achieve access to the other sex. Common baboons live in troops as do chimpanzees. The baboon troop, like troops of most mammals, is predominately a matrilineage, related females, while the males have entered the troop from another troop. Chimpanzee troops, on the other hand, are patrilineages, groups of related males, with females having come from elsewhere. Chimpanzee troops are ordinarily dispersed over a large territory while the more familiar usage of “troop” refers to a group that moves together.

Durable male-female pairs usually live away from other pairs, and when they do join larger groups, they are members of a flock, not involved or minimally involved in social interactions with others of the flock. Almost all the social interaction is between members of the pair. Animals in harems or troops, on the other hand, spend most of their time in same-sex interactions. Ordinarily these would be some variant of social competition for food among females and competition for females among males.

Humans, remarkably, have the ability to maintain durable pair bonds with reproductive exclusivity while living in larger social groups in which most of the day to day social interaction is with members of the same sex (Rodseth et al., 1991). Gibbons almost certainly could not do it: males are intolerant of the presence of other males and females of other females. Something special and now occurred in human evolution the led to our peculiar capacity to maintain pair bonds embedded in larger social groups.

Language - Much has been written about our unique capacity for complex communication using language. While small bits and pieces of such a faculty are present in other species we stand out from the rest of the animal kingdom with our unique capacity. It is intriguing to speculate about when we achieved this capacity. Unfortunately language leaves nothing in the fossil record, at least nothing that we understand so far. Some think that full modern language was the critical new trait that enabled the diaspora of modern humans out of Africa about 45 thousand years ago, a view that was fueled by the description of a gene, FOXP2, that is necessary for full language production. Subsequently this gene was sequenced in a Neanderthal, who was found to have the same sequence as that of modern humans. The discovery of a Neanderthal hyoid, a small bone in the throat central to the mechanics of the musculature of the tongue and throat necessary for speech production, has dampened speculation that Neanderthals did not have full language. In spite of the importance of language for our species there is remarkably little to be said about it here.


The Appearance of Modern Humans


We are fascinated with the appearance of modern humans, our own species. When did we evolve, and where? What was the ecological basis for the spread of our species over most of the earth within 30 thousand years of the movement out of Africa? An unspoken assumption of much of this discussion is that there was some sudden dramatic event, some quantum leap, separating modern humans from the ancestral species. A corollary of this assumption is that once we appeared we stopped changing and that evolution more or less came to a halt. Neither one of these assumption is credible: we continue to evolve and indeed human evolution seems to have speeded up since the diaspora and especially since the widespread adoption of cereal grain agriculture. There is no clear break point.

Some argue that the critical step was the appearance of prepared core technologies less that half a million years ago. The first unambiguous evidence of control of fire, hearths, appears at about the same time. Somewhat later skulls that look much like those of modern humans are found in Northeast Africa and in the Levant, together with scattered evidence of behaviors like the use of ochre for body decoration, apparent beads, and scratchings that are clearly designs. As if a coherent package finally came together, at 45 thousand years ago our ancestors left Africa and colonized the warm and temperate parts of the old world. There were at least two major thrusts, a northern branch into Asia north of the Himalayas and into Europe and a southern branch that may have followed shorelines around the Indian ocean to occupy Australia, New Guinea, and many of the nearby islands in the Pacific.

While the northern branch brought with it many innovations in technology and adornment that soon led to what archaeologists call the “creative explosion” in Europe, the southern branch had little or no sign of any new and different adaptation: their technology was no improvement on that of European Neanderthals. Some archaeologists, most notably Richard Klein of Stanford University, see the origin of modern humans in the technology and art of the European Upper Paleolithic, but such a view must deny that the members of the southern branch of the diaspora were modern humans.

What is to be made of the fine tools and exuberant decorative art and adornment of the northern branch of the diaspora? As we discuss in a following chapter, a fruitful way to divide cultures of the world is into those where males work to provision their families and those where males are more occupied with subtle and not so subtle forms of competition with each other. The latter are found in ecological situations where women can feed themselves and their children, and even the males. These are mostly gardening cultures but the complex is also found where there are periodic rich resource streams that can be harvested without a lot of effort by groups of males. Horse cultures on the North American Great Plains exploiting bison and Indians of the Northwest coast exploiting salmon runs are familiar examples.

In the latter male-competitive groups there is often elaboration of costumes and decorative arts: think of the colorful bonnets of the plains or the elaborate poles and boats of the Northwest. The sculptures like Venus figurines and the elaborate cave art deep in the earth of the European Upper Paleolithic immediately recall what we see in groups today where men can mostly live off the work of women. Perhaps the “creative explosion” is not so much an expression of new human capacities and abilities as it is an expression of life where men could withdraw from much of subsistence work and instead spend their days on doing “guy stuff.” If there is anything to this theory then the apparent backwardness of the people of the southern branch of the modern human diaspora may only reflect subsistence systems where males were busy working.