Who Were the First Humans?

A Magical "Paleo" Mystery Tour

By A.J.S. Rayl

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Since time immemorial, modern humans have wondered about the similarities shared with great apes and other primates, and the differences that make us rulers of the world. In the 1990s, Svante Pääbo set out to find the answer. In a landmark study, he sequenced random sections of the chimpanzee genome and compared them to human genome sequences to find they were, on average, only 1.2 percent different. While the sobering discovery made headlines and its implications began to sink in, Pääbo was “conducting some of the most exacting work ever attempted on the DNA of human and nonhuman primates.” That’s what J. Craig Venter, a leading figure in the decoding of the human genome and a 1999 Nobel Conference presenter, wrote in a 2007 Time magazine article that named Pääbo one of the “100 most influential people in the world.”

Meanwhile, Pääbo was already on another path that was taking him deeper into our past. It was a path he blazed himself in the mid-1980s while he was working toward his doctorate. Forever intrigued with Egyptian mummies and knowing there were quite a few of them residing in museums around the world, he decided to try and get a specimen to check out its DNA. “Just like we excavate physical sites to find fossils in Africa, we can do excavations in the genome to find out our history, things that we otherwise could never find out,” he explains.

Pääbo was the first to ever attempt such a thing and the first to succeed. He isolated and analyzed the DNA of a 2,400-year-old-Egyptian infant. It was a momentous achievement and it garnered him not only a Ph.D., but also eternal renown and, by most all accounts, recognition as “the father of paleogenetics.”

Since then, Pääbo has continued to develop and improve the methods for genome “excavations.” In 1997, he isolated the first piece of DNA from a Neanderthal, and in 2006 he further impressed the scientific community by announcing he had successfully decoded many random fragments of DNA from 40,000-year-old Neanderthal remains. These days, he and his colleagues are sequencing the entire Neanderthal genome, looking closely at certain genes we share in common, like the FOXP2 gene known to be involved in speech and language. Intriguingly, he says, the FOXP2 gene in Neanderthals resembles the human FOXP2 gene. “There is no reason to assume they wouldn’t have been able to speak much as we did, although there could have been other differences,” he admits. Imagine walking with the Neanderthals.

At the same time, Pääbo’s team has shown that Neanderthals and modern humans hailed from two distinct lineages, sharing a common ancestor some 650,000 years ago, another significant advance in the field. Once Pääbo and his team complete the entire Neanderthal genome, it will serve science for all time, allowing evolutionary insight into humans as well as our hairy cousin. “Some forms of analyses of the Neanderthal genome will allow us to look for positions in humans, after we separated from the Neanderthals, where a variance swept through quickly and became fixed, in other words became a characteristic all humans have today,” he explains. “Those will point to regions in the genome where selection or something important happened or changed in our ancestors that enabled them to survive or reproduce better.” Mining both the human and Neanderthal genomes will reveal important clues needed to learn how it is that we were able to survive and evolve.

While paleogenetics has been flourishing, paleoanthropologists and archaeologists have been burying old hypotheses with new evidence unearthed from their hands-in-the-ground research. Interestingly, even though the DNA detectives are still working to identify where in Africa the cradle of humanity first rocked and who the first immigrants to the Americas were, the researchers in the field are already heading for coastal environments—and their discoveries are changing the way we look at early humans.

Pinpointing Africa as humanity’s birthplace was genetics’ gift to the field-workers. “There is a recurrent pattern we find in the genetic analyses and we see that the progenitor population was bottlenecked to about 600 breeding individuals,” notes Curtis Marean. “This allows us, the field-workers, to take the climatic and environmental conditions of 140,000 years ago—which is the best estimate for that bottlenecked population—and make some well-informed, ecological predictions about where those populations might be and target our fieldwork to intercept that population.”

That’s exactly what Marean set out to do. He knew he needed a site higher than 10 meters above sea level, but one on the water. “At 123,000 years ago, the sea came up 6 meters on average, so, if you’re in a site that’s below 10 meters, the sediments are washed out by that high sea level, because you need to [account for] the high spring tide, storm surges, and sea spray,” he explains. “If you want coastal deposits older than 123,000 years ago, your site needs to be 10 meters above sea level or more.

In 1999, Marean found his site, a cave high in the cliffs at Pinnacle Point overlooking the Indian Ocean near South Africa’s Mossel Bay, within the area known as the Cape Floral Kingdom. “There are a lot of sites in southern Africa that postdate 120,000 years, but there hasn’t been anything older than that, particularly on the coast. When I walked into Cave 13B, on the right side or northern wall of the cave I could see an eroded deposit stuck to the wall. There were shellfish and bands of sands that I knew we could date with optically stimulated luminescence dating. I knew we were 15 meters above sea level and it looked old.”

As it turns out, Cave 13B was old and Marean found what he was looking for, and more. Last year, after seven years of effort, he and his colleagues reported their discovery in Nature: the early hominids occupying Pinnacle Point’s Cave 13B some 164,000 years ago were advancing on multiple fronts. “What is in many ways surprising, and in some ways is not, is that the people here look like they were behaving like modern humans,” he says. The inhabitants boasted at least three hallmarks of modern life: they ate seafood, used early tiny blade technology to harvest marine resources, and they also used ocher, a reddish pigment from ground rocks, known to be used for cave paintings and/or body adornment. Beyond finding the earliest evidence for the systematic exploitation of marine resources and some of the earliest evidence of ocher use, Marean’s discovery offers the earliest dated evidence, so far, of “modern” human behavior.

Culture, scientists believe, is in part what came to define humans as “modern,” and Marean’s unearthed treasures pretty clearly suggest that cooperative behavior and culture began much earlier than previously believed. Actually, Marean believes that Cave 13B’s ancient inhabitants may figure even more prominently in our story. “During this long glacial stage, this coastal area in South Africa was one of the key refugia regions for human populations,” he says, “and might have been the refuge for the progenitor population for all modern humans.”

The bottleneck population of 600 breeding individuals discovered by the paleogeneticists is unlikely to be scattered all over Africa, says Marean. “It is more likely they were a small group in one pocket or a place.” If he’s right, that means our forebears were fishermen and fisherwomen, not mammoth hunters and surfers, not hikers.

The Cape Floral Kingdom, the area in which Marean’s cave is located, is still recognized today as one of the world’s unique biomes or regions, with a number of distinct characteristics. “It is hyper-diverse and features an extremely high variety of geophytes, plants with tubers,” says Marean. “Hunters-gatherers loved geophytes because they’re big packages of carbohydrates and, because they were underground, they were less accessible to the other animals with which they competed for food resources.”

In addition to a rich supply of carbohydrates, protein abounds in the form of the shellfish on these far southern shores of Africa. “This confluence of carbohydrates and protein is rather unique,” he points out. So unique it may have also influenced their culture, specifically the population’s social dynamic, Marean suggests. “The foundation of the economic contract between men and women in most hunter-gatherer societies is that women produce the carbohydrate and the men produce the protein.” Turns out in Cave 13B, the women were probably collecting shellfish and thus providing protein, too. That might not seem like such a big deal. But they had to know the movement of the tides and learn how to harvest the tidal pools and not get washed out to sea when the tide came up and the waves crashed. In so doing, they may well have redefined the role of women, says Marean, and may have lived in a more egalitarian way, which in turn probably aided in the survival of Homo sapiens in ways beyond their ability to reproduce.

So why did they leave paradise?

No one really knows what compelled our forebears to migrate, but scientists now believe that between 50,000 and 70,000 years ago our ancestors took off from Africa for the rest of the world. The beaches, according to Dennis Stanford, never lost their appeal. “It’s just a whole lot easier for an anthropoid to make a living in coastal environments than out on the savanna, because you’re not competing with the lions and tigers and all the other heavy hitters. There’s plenty to eat and the weather is generally milder,” he says.

The notion that the first American immigrants arrived from Asia traveling across the Bering Land Bridge has been around so long that it’s usually taken as gospel truth. This tundra plain “appeared” as massive amounts of ocean water froze into the enormous glaciers of the last ice age, exposing the broad continental shelves now covered by the Bering Strait for several periods during the Pleistocene ice ages, effectively joining present-day Alaska and Russia. “But many roads lead toward knowledge, and the unexpected is often encountered along the journey,” says Stanford, who spent a good chunk of his career conducting research in Alaska, Siberia, and the Arctic in search of the evidence to support that hypothesis. “And that’s not entirely the way it happened, period. The data is just not there,” he says.

“The Bering Land Bridge hypothesis made sense in the 1940s, but it was never tested.” Humans did come in that way, he agrees. “But they came in late, and I think so many came in at the end of the last glacial age maximum, when the glaciers were receding, that they swamped people who were here. We’re finding that, from some of these early skeletons, there were what you would call archaic humans, like Kennewick Man, kind of generalized humans that hadn’t gotten into the genetic drift and isolation and the environmental adaptation that has sort of ‘colored’ what humans look like, their physical natures. It’s pretty clear from the physical anthropology that people came into the Americas from several different locations, including Europe as well as Asia, and that we have a much earlier mixing bowl than 1492,” he says.

After six years of “intensive research,” Stanford and Bruce Bradley presented their Solutrean Solution model at the “Clovis and Beyond” conference in Santa Fe, New Mexico, in 1999. “The earliest immigrants into North America came across the Atlantic Ocean from southwestern Europe along the pack ice that bound all of the land masses closer together some 21,000 to 16,000 years ago, and they brought their stone tool, hunting technology with them,” Stanford says summarizing.

By his reckoning, the fluted Clovis points used for hunting in North America around 11,000 years ago were not developed independently as had been theorized. Rather, Stanford says, they evolved from the advanced flaking techniques of Solutrean technology first developed in prehistoric Europe some 8,000 years earlier and named for the site in Solutré, France, where geologist and paleontologist Henry Testot-Ferry (the second son of Napoleon’s famous cavalryman, General Claude Testot-Ferry) discovered the first bifacially flaked stone projectile points in 1866. As these distant ancestors of ours first came “ashore” in America, they relied on these projectile points chiseled into form from stones, with stone, for hunting and protection, and along with their survival skills—which Stanford suggests were similar to those of the Inuit people of today—they managed to settle and grow their populations.

From the eastern coastlines of America, the first modern humans on these shores headed south and west and, as they did, evolved the Solutrean technology into what scientists define as Clovis technology. “It’s clear that these two technologies are so close,” says Stanford. Clovis points—first found in Clovis, New Mexico, and thus named—have been found in numerous places around the United States and remain the earliest advanced projectile weapons found in the Americas.

Not everyone in the community has accepted the Solutrean Solution model yet. Some skeptics cite gaps between the Solutrean technology, which dates to 19,000 B.C., and the known appearance of Clovis technologies some 11,000 years ago. But there are sites, such as Cactus Hill, that have yielded artifacts that appear to bridge both temporal and technological gaps between the two cultures. Moreover, new sites recently found along the eastern shore of Chesapeake Bay, as well as bones and a Solutrean-style stone knife recently dredged up from the leeward side of the ice-age barrier islands some 40 miles off of the coast of Virginia, continue to bolster their theory.

According to Stanford there is “a clear dominance” of Clovis technology on the East Coast. “There are more Clovis sites on the Delmarva Peninsula in Maryland than there are in the entire Rocky Mountains,” he notes. “We believe these first immigrants were pretty well working the marine and ice edge resources, including harp seals and seabirds such as the Great Auk. And it appears that there were even walrus rookeries on the Chesapeake Bay during the last glacial maximum, circa 22,000 years ago,” he elaborates. And, in September 2005, a Clovis point was found on America’s west coast in Malibu, California. It is the first Clovis point ever found in situ anywhere along the western coast of North America, and was recently radiocarbon dated to 9074 B.P. (before present).

“As we work through this, we’re probably going to find that, instead of mammoths, they were primarily after mollusks.” Ultimately, Stanford thinks digs will have to go underwater “to get at real answers” because of the rise of the sea level during the last glacial maximum. In the meantime, the search continues to inform, rewrite, and enrich the story of America’s first immigrants.

Marcus Feldman and colleagues at Stanford University, meanwhile, are digging into the human genome in the largest molecular study to date on genetic variation around the world. Their objective is to try and clarify the history of human migrations, pinpoint their paths, and figure out in the process from where exactly in Africa we emerged. They’re also looking at our genes to see how natural selection created the characteristics that distinguished us and/or allowed us to better adapt.

Interestingly, they have already shown very strong selection on genes related to skin color in Europeans and West Asians. “When you look at enough genetic markers, you can see patterns that show skin color genes—genes that control melanin,” Feldman explains. “They vary a lot around the world, but the ones that produce lighter skin seem to have been strongly selected after modern humans left Africa 60,000 to 70,000 years ago, probably in response to the climate difference; usually people think it’s related to vitamin D,” he says.

For some time now, Feldman’s lab has been also studying lactose and the human capability to digest milk, something that appeared with the development of agriculture around 10,000 years ago. “It’s clear that this is where cultural evolution—the development of agriculture and domestication of farm animals—has driven genetic evolution,” Feldman says. “Whether you use milk or not, dairying is a cultural phenomenon. If you ingest milk and don’t have the lactase persistent gene, you’ll suffer the consequences. Those societies whose cultures enabled them to use milk, mostly Europeans and West Asians, had an advantage that’s reflected in the genome, and it’s lasted a long time—9,000 years now,” he notes. Although the frequency of people who can digest milk is high in the United States, many people in other countries, including Africa and Asia, cannot digest it.

While they have not yet been able to conduct focused research on indigenous American populations, Feldman's lab has found that, in general, the various Native American tribes are “much different, one from the other, than other indigenous populations,” Feldman says. “That’s because they were small populations that separated during the migrations between 15,000 and 25,000 years ago and each group was founded by a small number and then didn’t come in contact with one another; therefore, we see a big difference between the American Indians and Central American populations and the Canadian populations,” he explains. “They are very different one from the other.”

In his work in human molecular evolution, Feldman has also homed in on the present, today’s modern humans, and especially on demographic work focused on issues connected with gender imbalance. Notably, he has a large research program on demographic issues related to the sex ratio in China, working in collaboration with Chinese demographers on both modeling and survey work. Given China’s population problem and government-enforced restrictions on reproduction, and the society’s cultural preference for male children, the findings are foreboding.

Since our brain is the one clearly unique asset that set us apart from all God’s creatures great and small, researching its evolution has been something of—well, a no-brainer. For more than a century and a half, it was generally believed, especially within the cognitive and neurosciences, that the brain evolved strictly as a result of ecological needs and demands and to process factual information about the world. Today, that notion is headed for extinction.

For one thing, evolutionarily speaking, it cannot account for the size of our brain. “You don’t even need the brain the size of the average monkey to survive,” points out Robin Dunbar. Yet, the human brain, which accounts for a mere 2 percent of the body, demands and consumes 20 percent of the fuel. “You just don’t need something as big and expensive as the human brain to survive in the world,” Dunbar says.

What, then, is the extra that you’re getting out of paying this enormous cost?

“Our ability to live in the virtual world of the mind,” says Dunbar, answering the question with the key concept from the Social Brain hypothesis he put forth in 1998. “It’s sociality in the end and that depends on having a large ‘computer’ that gives us the ability to step back from the physical world and into the virtual mental world, which enables us to imagine there are other worlds around us that we can’t actually physically see,” he contends. “Where other species have their noses thrust up against the grindstone of that world, we can step back and ask, ‘Can it be different?’ Coming out of that you have everything—drama, literature, science, and religion. The questions that remain are, why do we have that capacity and when did it come about?”

More than any other concept, the Social Brain hypothesis bridges both our evolutionary history and contemporary experience, and Dunbar is currently looking from all angles to get at the answers to those remaining questions. As director of the British Academy Centenary Research Project “Lucy to Language: The Archaeology of the Social Brain,” he has brought together social psychologists, behavioral ecologists, social and biological anthropologists, sociologists, linguists, historians, and musicologists with palaeolithic archaeologists and evolutionary psychologists to explore these two axes of the human experience. They’re looking to see what they can find out about how the early hominid brain evolved from its essentially ape-like beginnings among the earliest australopithecines around 3 to 5 million years ago to the modern hominids of the Upper Palaeolithic Revolution around 50,000 years ago, and to its final expression in the dramatic social and economic changes of the last 10,000 years.

“We’re still struggling with an impossible task,” Dunbar says of the seven-year project. “The most interesting thing that’s actually come out in the last year is the finding that, in all of the species of birds and mammals, it’s the monogamous, pair-bonded species that have the big brains,” he offers. “But this isn’t true of primates. In primates, you have this quantitative relationship between group size and brain size. We think primates have generalized the pair-bonded relationships, which are reproductively oriented in the normal case, if you like, to non-reproductive individuals to create nonreproductive pair bonds—in other words, friendships. That’s why you get this quantitative relationship.”

Due to their highly social nature, nonhuman primates have to maintain personal contact with the other members of their social group, and it is generally believed that our sociality is integral to being human as well. But as big as our brains may be in comparison to most other species of animals, they can only get so big. In exploring that limit, Dunbar developed a kind of theorem. Known as "Dunbar’s Number," it essentially states that there is a cognitive limit to the number of individuals with whom any one individual can maintain stable social relationships.

Despite the fact that over the last few millennia our groups have gotten increasingly larger while our brains have not, our “groups”—take a city like Chicago, for example—have become more dysfunctional, Dunbar points out. Technology, however, may be able to break through the physical limitations of Dunbar’s Number, even if not our dysfunctionality. To determine whether that’s possible, he is also working on two “big projects” looking into whether the electronic media might enable humans to break through the current constraints of human sociality.

The evolution of the brain is more than a physical feat, however, and Dunbar is working to get deeper inside the three-pound universe. Before he'd gotten halfway through the Lucy project, he helped plan, and launched, a new project, “Identifying the Universal Religious Repertoire,” which got under way earlier this year to explore the emergence and role of religion and its impact on the human brain.

As a theologian interested in science, J. Wentzel van Huyssteen has long been certain that there are connections to be made between the physical sciences and religion. Forever intrigued with human origin, he’s been working for years to connect themes common to the Christian way of life to culture, art, and science and has been widely honored for doing so. Now, his intrigue has come of age.

“Where it was previously politically incorrect to talk about human uniqueness in hominid history, scientists are now freely talking about uniqueness of our species—or species specificity—and trying to discover what it is about humans that is species specific or truly different, even as we acknowledge our ties to other animals,” he says. “I realized there were overlaps in theology and theological anthropology that resonated with science and that, while there are vastly different discourses in theology and paleoanthropology and archaeology, they are asking the same question—what makes humans unique? There is something to be learned here,” says van Huyssteen, who has been bestowed with a Templeton award and grants for his efforts.

In theology, he says, “the place of the human has always been seen as fairly abstract, while in science humans have always been very carefully and more empirically described in that we come out of this Earth. It’s so much more embodied.” Bringing those two together in interdisciplinary conversations, van Huyssteen says, offers “much promise” for our continued evolution. Moreover, he adds, “it’s fascinating to learn and to see how much of this was anticipated by Darwin, even though so much of it is coming to the fore now.”

Although Darwin is still condemned—often without actually being read—particularly within fundamentalist congregations or among those flocks who subscribe to the notion of intelligent design, those are denunciations van Huyssteen views as little more than “problematic” and “polarizing.” In his own way, he has responded by teaching “Theology and the Challenge of Darwinism,” a course at Princeton that he created.

“On my first day at Princeton, someone asked me, ‘What do you think of evolution?’ I can honestly answer: I think that’s the way God creates. And I find that invariably once my students actually read Darwin, they become fascinated and gain much more respect for the complexity of evolution and how Darwin saw it and wrote about it through his own worldview,” he says.

Worldviews have a lot to do with the intensity of some beliefs and how religious texts are read and viewed, says van Huyssteen, who believes the Bible should not be interpreted literally. “Biblical texts are very powerful and if they are read in a way that they’re believed to be true, which is literally, then you get creationism and the elevation of the Bible into the supernatural,” he says. “It’s very hard to break down that philosophical position and make someone realize that what they take to be the truth of the text is actually the truth of a worldview and that it could be beneficial to stand back and ask, like with any literature or art, if this is not the best way to read this, then how should we read it? Worldviews have influenced religious texts throughout the centuries and it’s important to consider that in reading the scriptures.”

For van Huyssteen, the great divide between religion and science that still exists in the United States serves no good purpose. “If we see God as the creator of everything on this Earth, then it is ludicrous to deepen this polarization,” he says. “The God of science should also be the God of who we humans are and the God of religion. It’s much more exciting to take the past and find connections between this evolutionary process and worldviews that could be more fruitful.”

Like no other species that ever dominated the Earth, we are impacting the planet and all life on it—including ourselves. Along the way, for better and worse, we are evolving. We may now be kings and queens of the world, but our ultimate survival is hardly assured. As we continue the journey into the new millennium, learning about our past and from whence we came takes on newfound importance, and answers now being found may serve other potentially dramatic purposes.

“To know why it is we came to be as we are, particularly given that we have effectively taken over the world as a species, is more than just intrinsically interesting," says Dunbar. “If people come to understand just how serendipitous the whole history of human evolution was, that extinction is the rule, then they might view how they affect the world around us rather differently. Going back to Lucy, and beyond her to the common ancestors of the great apes, waves of incredibly successful groups of early hominids just disappeared, one after another. Neanderthals were around for longer than we’ve been around and they bit the dust. At any number of points we could have easily died out as a lineage and slipped out of existence.”

More than that poignant realization is also relevant, Dunbar continues, in terms of how we relate to the rest of the planet. “Appreciating where we came from may give us a better understanding for life on Earth as a whole, how integrated it actually is, and how important it is to maintain things like diversity,” he suggests. “Perhaps it can also make us a little more humble about what we can actually achieve and what the risks are in terms of the species.”

The relevancy of human origins today is something that van Huyssteen has thought a lot about over the years. “I was asked 20 years ago in South Africa why this interdisciplinary conversation between religion and science was so important when the country was burning and apartheid was tearing it apart,” he recalls. “Today, of course, global warming, the energy crisis, and other such big problems are politically and otherwise dominant—rightly so. But I have always felt that we have an ethical responsibility as scholars from different fields to keep research going and to find out what advances and progress we might attain through interdisciplinary discourse in order to move our culture forward. The question of human origins and human uniqueness eventually plays into what we believe about human nature—who are we as humans —and what we should learn from the sciences and that also is discovering our ethical responsibilities. So, even something that sounds as esoteric as human origins and uniqueness is of fundamental importance, not only for who we are, but also ethically."

The call of our wild past is beckoning. Our ancestors survived by adapting, by leaving the forests, it appears, and learning to harvest and travel by seas. How will we adapt to the ever-changing environments of our bodies and our planet?

“Paleolithic people had fewer distractions and they were able to watch and learn from the environment, so in the past they were able to adapt,” says Stanford. “We have lost the environment. Our attentions have turned to our machines, BlackBerrys and cell phones, computers and Xboxes. “Kids today have stuff coming at them—bang, bang. It’s an increasingly frenetic world and children are growing up with attention deficit disorders and other learning disabilities because of our flash. Everybody wants a sound bite and nobody wants to concentrate.”

Environmentally, there are also those inconvenient truths of global warming and overpopulation. “Today we are facing an environmental cycle that we have created,” says Marean. “The world is growing to 15 billion people by 2050 at the same time the planet is globally warming—this is a serious crisis.

But one thing that makes humans unique is that we’re hyper-cooperative and we will engage in cooperative acts without an obvious immediate, individual return, Marean notes. “Humans also seem to have an innate desire for fairness and some geneticists even believe they’ve found a ‘fairness gene.’ These characteristics are fascinating because they really bump against what we would predict from evolutionary theory. Out of what context does that arise? The feeling of fairness and unfairness is hugely important to how we behave on a day-to-day basis.”

Are those characteristics what gave our distant ancestors the edge? How? And, might they continue to give us an edge?

“The understanding of what makes us unique, those funny traits like fairness and cooperation evolved somewhere, somehow, under some condition,” Marean muses. “Our progenitor population probably survived that crisis long, long ago through social cooperation at the small group level. Understanding why and how gives us insights into ourselves that can have practical applications today, because if we are going to survive this next environmental crisis, it’s also going to be through cooperation, only this time it will be at the global level.”

Creating a functioning global village is far easier said than done. As with all the primates, human success is founded on communality, on creating communal solutions to problems of living, surviving and reproducing, agrees Dunbar. “But our species has done that mostly by creating these small, very intensely bonded communities that are prepared and willing to give up something for the common good,” he says. This community, he says, creates “a kind of social contract system” that defines “the wider need for everybody to collaborate and cooperate” and that, in turn, “creates an inevitable tension between the selfishness of free-riders,” those few bad apples who can “steal a mark” and get something for free.

The free-rider problem, Dunbar points out, is everywhere. We’ve all had the experience. “It extends from a small scale, those who don’t buy a round in the pub when it’s their turn, to the global, multinational corporations cutting down the tropical forests,” he says. All in all, he adds, “free-riders have probably been the biggest problem that we’ve had to cope with through our evolutionary history and a lot of what we do and how we work seems to be designed to counteract the free-rider problem.”

As we evolve into the future, our survival may depend on our ability to intensely bond in a more global way. Impacting our capacity to do that is that cognitive limit to the number of individuals with whom any one of us can maintain stable social relationships. While no precise value has been proposed for Dunbar's Number, 150 is commonly cited as the approximate figure for humans. “This limit is a direct function of relative neocortex size, which limits group size,” says Dunbar. “The limit imposed by neocortical processing capacity is simply on the number of individuals with whom a stable interpersonal relationship can be maintained.” Group sizes larger than this generally require more restricted rules, laws, and enforced policies and regulations—in other words, a lot less personal engagement—to maintain a stable cohesion.

However we manage it, stable cohesion is something humankind has yet to perfect. While we may all be much more the same than different, some research is showing how small scale the world in which we live is, Dunbar says, and how many of the designs of the human mind relate to supporting and reinforcing these very small-scale worlds. “So we’re stuck in this awkward and ambivalent position where on the one hand a lot of our mechanisms are designed to create them-versus-us divisions; but, on the other hand, many of the aspects of social evolution and some other aspects of our mental design are designed to be more inclusive. So you can see why we have these them-us things emerging so easily.”

Still, at the end of the dig, it is a small world after all. “The overwhelming majority of differences among individuals occur within populations and even then the variation that’s between these ancestry groups or continents is like a drop in a barrel of water,” Feldman says. One of the things all this research is indicating, he expounds, “is that we need to change the way we look at each other—person to person, country to country, culture to culture—and redefine the differences among us.” For starters, he cites the need for eliminating the concept of “race” from our descriptive efforts, as well as our vocabulary. It’s not just a matter of being politically correct, rather there’s a strong logic behind the concept.

“Defining ancestry groups is just a more careful, a more responsible way of distinguishing ourselves from a biological point of view than by ‘races,’” Feldman says. “Since we can now be more precise about genomics and identify people who have ancestry in this place or that place or in more than one place, a more appropriate term is ‘ancestry groups.’”

For all the problems and bleak projections, there is hope. “We understand how flexible human beings are and how they can adapt to any situation other than loss of water,” says Stanford. “I don't know what the answer is, but I still have faith in human adaptive qualities.

“We need to learn and accept that plants and animals are part of us, too, and not consider them property,” says Stanford. “We need to get beyond this greed that is everywhere. If we begin to understand from a scientific as well as spiritual point of view that we’re all related and we’re all the same people despite some genetic and physical differences, we’ll all be better off.”

The future of humanity—our future—is, as it always has been, up to us.

A.J.S. Rayl is a freelance science journalist, writer, and author based in Malibu, California. She has written on assignment for a variety of magazines, including Air & Space, Astronomy, Discover, Psychology Today, and Smithsonian, and online ventures, including The Planetary Society’s http://planetary.org.

Svante Pääbo

Svante Pääbo

Professor of genetics and evolutionary biology and director, Max Planck Institute of Evolutionary Anthropology (MPI-EVA), Leipzig, Germany

Curtis Marean

Curtis W. Marean

Professor, Institute of Human Origins, School of Human Evolution and Social Change, Arizona State University, Tempe

Dennis Stanford

Dennis Stanford

Curator of archaeology and chairman of the Anthropology Department at the National Museum of Natural History, Smithsonian Institution, Washington, D.C.

Marcus Feldman

Marcus W. Feldman

Burnet C. and Mildred Finley Wohlford Professor of Biological Sciences and director, Morrison Institute for Population and Resource Studies, Stanford University, Calif.

Robin Dunbar

Robin I. M. Dunbar

Professor of evolutionary anthropology and director, Institute of Cognitive and Evolutionary Anthropology (ICEA), University of Oxford, United Kingdom

J. Wentzel van Huyssteen

J. Wentzel van Huyssteen

James I. McCord Professor of Theology and Science, Princeton Theological Seminary, N.J.