How to Tame a Fox (and Build a Dog)

by Lee Alan Dugatkin

  As a stream of groundbreaking findings about the course of human evolution made big news in the 1960s and ’70s, Dmitri had formulated a theory about how humans had become such sociable beings; his work with the foxes suggested to him that we had, in essence, domesticated ourselves, and it all began with selection for tameness. His theory was based primarily on conjecture. But then, peering into the social lives of our ancestors in the prehistoric era, before they began to speak to us through the stories they carved in stone, is by necessity driven, at least at the start, by conjecture.

  We may never know exactly when they first began to talk to one another, or to think in self-reflective ways, considered one of the hallmarks of distinctively human consciousness. We will never know for sure what stories they told one another around the fire at night, or exactly which songs they may have sung. But we do know that many forms of social ritual bonded them. They invested considerable care and time into the creation of works of art, making jewelry, carved figurines, and evocative paintings, such as images of distinctively human hands traced by red ochre paint, found on the walls of caves in many places around the world. Some of the oldest of these found to date, in the El Castillo cave in Northern Spain, date to approximately 40,000 years ago. Our ancestors also spent considerable time fashioning musical instruments, such as flutes carved out of animal bone, the oldest of which also date back about 40,000 years. And they saw their loved ones off in death by burying them with important items used in daily life, such as stone and animal bone tools, as the people living on the shores of Lake Baikal 8,000 years ago did with their dogs.

  As Dmitri prepared to unveil his idea, the fact that a number of other proto-human species had evolved, and that some of them may even have lived alongside Homo sapiens, was only beginning to become accepted. The first Neanderthal fossils had been discovered way back in the early 1800s, but suddenly a number of major finds were painting a more complex picture of the proto-human family. Dmitri had read avidly about these discoveries and he thought his theory that we Homo sapiens had domesticated ourselves, fostering the strength of our social bonds, might explain why we were the one proto-human line that survived.

  Louis and Mary Leakey made some of the most important of the discoveries of new proto-human species. Working in the Olduvai Gorge, in Tanzania, they uncovered a number of bones and skulls, as well as tools, which shed much light on the surprising diversity of proto-human lines. Mary made their first big discovery, in 1959, of the skull of a species that clearly evolved from a large primate.3 But the shape of the skull was so different from that of the human skull that they concluded it could not be a direct progenitor of our line. It had an enormous jawbone and a pointed crest of bone running front to back along the top of the skull, known as the sagittal crest. Earlier researchers who had discovered skulls in South Africa with the same feature in the 1920s had concluded that this crest indicated that it acted as a kind of anchor for very strong, large muscles that ran down to the jawbone and were attached to it. Its bite would have been extremely powerful, which is why the Leakeys nicknamed the creature Nutcracker Man. The official name they gave to the species was Zinjanthropus boisei, meaning East African Man, and the discovery not only made front-page news all over the world, catapulting the Leakeys to fame, it caused a huge stir among experts in human evolution.

  At this time, the idea that humans had descended from an ancestor in Africa was not widely accepted. Darwin and his colleague Thomas Henry Huxley had conjectured that our ancestors had likely evolved there because that was the only continent on which our nearest contemporary primate relatives are found. But paleontologists had discovered fossils of Neanderthals, in 1829, in Belgium, and then in other areas of Europe. The species got its name from the Neander Valley in Germany (thal, in German), where a Neanderthal skull was found in 1856. The skull of a different species that seemed to be proto-human was found in Indonesia, then called Java, in 1891, and given the moniker Java Man.

  Excavations that began in the 1920s in a cave in China, near Beijing, produced another skull of this species, dubbed Peking Man because the city was at that time called Peking. This species was thought to have walked upright, so was named Homo erectus. Large piles of animal bones were found at the site, and some of them had char marks that suggest they resulted from cooking. Because the remains of different apparently proto-human species were found in such disparate locations, some researchers concluded that humans had evolved in various locations.4

  In the 1960s, the Leakeys made their next major find, a jawbone and other fragments of a skull that was more human-like, as well as some hand bones. They argued the skull pieces found at Olduvai indicated that this species had a very large brain, and that the hand bones revealed it also had a good grip. They theorized that this species must have made some of the stone tools they had found in the area, leading them to name the species Homo habilis, “habilis” being the Latin for handle, nicknamed “handy man.” Leakey and other researchers asserted that this species and Nutcracker Man, Zinjanthropus boisei, had coexisted, refuting the notion of a single line of evolution. Other anthropologists objected vigorously to this assertion, but as more fossils of both species were discovered, the Leakeys were proved correct.

  One of the big open questions about the transition from more ape-like to more human-like species was when our ancestors had first started to walk upright. The Leakeys made important finds on that front, the first of which was a fossil of a Homo habilis foot bone, which suggested that it had walked upright. But the most startling evidence was uncovered at a site in the vicinity of Olduvai that Mary had begun to excavate a few years after Louis passed away in 1972. At this site, called Laetoli, Mary had in 1976 discovered a path of fossilized animal footprints, preserved in stunning definition by volcanic ash. When a colleague, Paul Abell, was investigating the prints one day, he noticed that one of them looked remarkably like that of a human foot. Further excavation revealed about seventy of these prints, looking eerily like a path of human footprints left in sand.

  Perhaps no paleontological find has ever more evocatively transported us back in time. Close analysis revealed that the prints were made by three different beings, and that the toes, heels, and arches of their feet were in fact very much like those of human feet. There was little question that this species had walked upright, and the prints were made about 3.6 million years ago.

  Because no fossilized bones of a hominid were found with the footprints, the species that had made them couldn’t be identified. But evidence was that it must have been the species we now know as Australopithecus afarensis, the most famous member of which is named Lucy. A few years before the Laetoli footprints were discovered, the paleoanthropologist Donald Johanson spotted what was clearly an elbow bone jutting out of the ground at the excavation site he was investigating near the village of Hadar in Ethiopia. He and his team eventually uncovered the skull and much of the rest of a fossilized skeleton of a female hominid, which they named Lucy because during a party celebrating the find that night, a stereo nearby was repeatedly playing the Beatles song “Lucy in the Sky with Diamonds.”

  Just under four feet tall, Lucy likely had quite a small brain, given the size of her skull, but her skeleton also clearly indicated that she had walked upright. This was stunning for two reasons. One was how old the remains were, roughly 3.6 million years,5 which was much earlier than paleontologists had thought our ancestors had first stood erect. The other was that anthropologists had expected that walking upright had evolved after the brains of hominids had grown more substantially. Lucy, some paleontologists now said, might have spent some of her time swinging through tree branches, as indicated by the size and shape of her shoulder bones. She was a remarkable link between the more ape-like species of proto-humans that had been discovered and our closer ancestors in the homo family. Lucy’s bones dated to the same timeframe as the Laetoli footprints, and when Donald Johanson and his team compared the size and shape of Lucy’s feet to those prints, some of them m
atched very closely.

  Study of Lucy’s bones and other bones of her species has revealed that Australopithecus afarensis children matured a good deal faster than human children do. So our evolution into humanness likely involved a delay of maturation, as was seen with so many of the characteristics of the tame foxes.

  Belyaev thought the evidence suggested that humans had evolved largely through the process of destabilizing selection. In 1981, he published a scientific paper presenting this theory, and for his keynote speech at the XV International Genetics Congress in 1984—an honor given to the organizer of the prior Congress—he made the case in greater detail.6

  In Belyaev’s view, our ancestors had come under new stresses as their bodies and brains evolved. As they became more social animals, living in larger groupings required a moment-to-moment negotiation of a panoply of social interactions. The pace and complexity of the changes were not brought about primarily by the small increments indicative of natural selection operating on changes that resulted from single gene mutations. That had certainly played a role. But, he thought, the transformation through that process would have taken longer than the approximately four million years from the emergence of the earliest hominids, the Australopithecines, to modern humans. He wrote in the article, “This becomes especially obvious when taking into account that in the course of evolution such complex multi-gene determined anatomical and physiological structures were involved, such as the system of movement and orientation of the body in space, hand function, the structure of the skull, larynx and vocal cords and tongue.” Bolstered in part by King and Wilson’s discussion of the human and chimpanzee genome, Dmitri argued that destabilizing selection must have been at play, working through dramatic changes in gene expression. In his keynote address, he proclaimed that the huge number of changes in both body and behavior “involved not so much the structural as the regulatory elements of the genome.” And those regulatory elements are mostly about gene expression patterns.

  He thought the first major change was the transition by the Australopithecines to bipedalism—starting to stand upright. He argued that this involved not only the transformation of the entire motor system—both the nature of our bone structure and of our muscles—but also the emergence of important new brain abilities, particularly those involved in balancing upright. The mastery of this skill, he continued, then led to two new capabilities that were crucial in catalyzing further changes: the ability to see wider and farther and the freeing up of the forelimbs, which in time evolved into hands. Natural selection would clearly have strongly favored the emergence of these changes as they provided so many survival advantages. The acquisition of these new talents, he argued, then had a dramatic effect on the further development of the brain, pointing out that Homo erectus, which at the time was thought to have emerged about 1.3 million years ago,7 had a brain a great deal larger than those of the Australopithecines.8 So large had Homo erectus’s brain become that it was almost the size of our current Homo sapiens brain. This massive brain growth was accompanied by additional major changes in the body, such as the organs involved in the sensory functions and in speech—which included a substantial increase in the size of the larynx and a repositioning of the tongue—as well as the refinement of the motor skills of the forelimbs. This was vital, along with the emergence of better cognitive abilities, in allowing them to begin making tools. The interplay between the brain and body was at the core of his account. He wrote in the article, “We can say that if the body created the brain, and the individual mind generated by it, then the brain, in turn, is strongly influenced by the body functions.” And that feedback loop had led to acceleration in the rate of change. He was keen to note that while the Australopithecines had evolved over the course of several million years, Homo sapiens had evolved into modern humans in less than two hundred thousand years.

  Belyaev knew that many would think he was already stretching the limits of his destabilizing selection theory and what it might account for in our own evolutionary history, but Dmitri was not through yet. Never one to shirk what he saw as his duty as a scientist, he thought that this was an important enough issue to take some conceptual risks: time would tell whether he was on the mark. Dmitri next proposed that the combination of new talents he discussed had facilitated an intensely social way of life. These earliest humans organized themselves into larger social groups and developed many rituals, including religious practices, as well as making increasingly sophisticated artwork, such as the gorgeous cave paintings at Lascaux and Chauvet in France, making clothing, and developing more elaborate language. “The social environment,” Dmitri said in his keynote speech, “created by man himself has become for him quite a new ecological milieu.” In this speech he suggested, “Under these conditions, selection required from individuals some new properties: obedience to the requirements and traditions of the society, i.e., self-control in social behavior.” These “new properties” destabilized the system, selecting for dramatic changes in behavior, which Belyaev thought likely occurred via changes in gene expression. This is where he makes a key connection to the process of domestication and self-domestication.

  Humans who were better able to cope with the new stresses, to stay calm, cool, and collected rather than striking out in aggression, now had the selective advantage. “One can hardly doubt,” Belyaev mused, “that the ‘word’ and its meaning has become for man an incomparably stronger stressful factor than a club blow for a Neanderthal man.”9 Calmer, cooler-headed members of communities were selected for, he proposed, with results similar to the effects of the artificial selection for tameness in the foxes. As with other domesticated species, this selection pressure led to lower levels of stress hormones, and it favored anything that prolonged our juvenile, more carefree, less aggressive stages of development. We also, like other domesticated species, can breed all year round. Essentially, we are domesticated, but in our case self-domesticated, primates. We sped up the process, Belyaev argued, domesticated ourselves even more quickly, because we, in turn, preferred tame partners as our mates.10

  Primatologist Richard Wrangham has recently written about how just such a self-domestication process may be under way in another primate species, the bonobo (Pan paniscus), one of our closest evolutionary relatives. In 2012, he collaborated on a paper—“The Self-Domestication Hypothesis: Evolution of Bonobo Psychology Is Due to Selection against Aggression”—with a former PhD student of his, animal cognition specialist Brian Hare.11

  Bonobos live a peaceful, one is tempted to say even enjoyable, life. They too have a fission-fusion society. Bonobo society is completely matriarchal, with females forming alliances amongst themselves. If a male has standing in a bonobo society, it is primarily because the females in the group permit it. Bonobos play all the time. They voluntarily share food, even with strangers. And sex is everywhere. But most sex isn’t about copulation between a male and a fertile female. Homosexual sex among females is quite common, as is heterosexual sex between young and old, involving kissing, oral sex, and rubbing the genitals of a partner (either homosexual or heterosexual): primatologist Frans de Waal has quipped “bonobos behave as if they have read the Kama Sutra, performing every position and variation one can imagine.”12 Sex is the glue that bonds bonobo groups together. It is used as a greeting, it’s a form of play, and it resolves conflicts that emerge. In this regard, bonobos are strikingly different from their close relatives, the chimpanzee.

  Chimp society is patriarchal, males are violently dominant to females, they constantly fight one another to rise up the male hierarchy, and sex is about procreation. Males often form alliances, but unlike the female coalitions in bonobos, such alliances raid and viciously attack individuals in other groups. In bonobos, though intergroup interactions are sometimes nerve-wracking, in most instances they are peaceful gatherings, sometimes even involving copulations.

  How could two such close genetic relatives have evolved along such different social trajectories? Wrangham and Hare
became obsessed with finding an answer.

  A molecular genetic comparison of the genome of chimpanzees and bonobos mapped onto an evolutionary tree suggests that they began to diverge from a common ancestor approximately two million years ago, at about the same time the Congo River was forming in Africa. The river split up the population of their common ancestors into two groupings, with those that evolved into bonobos living in a small area to the south of the Congo River, while those that evolved into today’s chimpanzees lived north of the river and over a much larger area that stretched across west and central Africa.13 Hare and Wrangham argue that by the luck of the draw, the bonobo lineage back then ended up with a huge advantage when it came to procuring food. Their territory boasted higher-quality plant foods. And what’s more, they faced less competition for food. There were no gorillas where bonobos lived and so, unlike chimpanzees, they did not have to compete with their larger primate cousins for food.

  In this world of relative plenty, with little competition over food, play, cooperation, and tolerance of others were advantageous. Bonobos who played during free time and cooperated with one another to obtain food, shelter, new friends, and sexual partners when play time was over, fared better than aggressive intolerant types. This selection for tameness led to changes in their bodies and behavior that are strikingly similar to the changes in the foxes.

  Compared to chimpanzees, bonobos have more juvenile skeletal features, lower stress hormones levels, and altered brain chemistries. Like the tame foxes, bonobos also have a longer developmental period in which they rely on their mothers, show more variation in color (white color tufts and pink lips), and have smaller skulls, yet, remarkably, still have more gray matter in their brains devoted to areas linked with empathy than do chimps.14 Hare and Wrangham go on to propose that over time, bonobo females may have selected the least aggressive, most friendly partners of the opposite sex as their mates. They may have self-domesticated themselves, in a process similar, but certainly different in the details, to that Belyaev outlined for human self-domestication.15 Future work on whether bonobos have indeed undergone this process of self-domestication might, as Hare and Wrangham note, look at the role of gene expression and aggression, how neurobiological and hormonal differences affect aggression and tameness, and the intricate details of why behavior and morphology are so closely linked in both chimps and bonobos.