Once upon a time (about seven to nine million years ago) the bountiful land of Tuscany was joined with Corsica and Sardinia to form an island. It was the northernmost in an archipelago that spanned the Mediterranean Sea, linking what was to become Europe with ancient Africa. The inhabitants of that long-vanished isle—Tuscinia we might call it—read like creatures from a fairy tale. Giant dormice and vegetarian bears roamed Tuscinia’s hills in the company of pygmy hogs and archaic pikas, while on more southerly isles carnivorous hedgehogs the size of collies and exotic animals such as the goat-like Hoplitomeryx thrived. This last creature was distinguished in its possession of wolf-like canine teeth and five horns (including one over each eye and one in the middle of its forehead).
None of this would matter very much to contemporary science were it not for the fact that Tuscinia was also home to an eminently curious primate. Its bones, which long puzzled scientists, were first unearthed over a century ago by Italian coal-miners. More recent discoveries from Tuscany and Sardinia, however, indicate that Oreopithecus bambolii, as the macaque-sized creature is known, was an unusual ape.1 What is astonishing about it is that, like us, it habitually walked upright, perhaps using its hands to carry food to a safe place to eat, or holding a shady leaf over its head on hot days. It was as if, before granting the entire planet a later model of upright ape, nature had embarked on an insular experiment.
Oreopithecus stood and walked in a fundamentally different manner from ourselves, for rather than having the great toe aligned with the other toes (in the manner convenient for filling shoes) Oreopithecus’s great toe was large and stood out at an unexpected 90 degrees. In effect it formed the third prop of a stable tripod upon which the creature balanced. These odd Tuscan primates were probably an evolutionary dead end, meeting their doom in the form of the cats and hyenas that reached their island home from Africa or Europe when the Mediterranean Sea dried out around six million years ago. Oreopithecus was, however, just one species among many kinds of apes (known as hominoids) that once thrived in Europe. Their remains have been found from Spain to the Caucasus, where some, at least, inhabited open forests and woodlands.
We are all familiar with the dominant hypothesis of how walking evolved, even if only through the transition from knuckle-walking ape to upright human that is depicted endlessly in advertising. In his remarkable new book, Lowly Origin, Jonathan Kingdon, taking into account 150 million years of evolution, reexamines the question of “where, when and why our ancestors first stood up.” The book borrows its title from the final words of Charles Darwin’s Descent of Man—that human beings, with their “exalted powers,” still bear in their bodily frames “the indelible stamp of [their] lowly origin.”
Not every book on evolution bears a nude self-portrait of its author on the cover—and probably for good reason. Lowly Origin gets away with it because “Nine-foot Jonathan” (as Kingdon is known around Oxford) is an accomplished artist and anatomist who uses images of his own body throughout to make an evolutionary point. Since he is an autodidact who has spent much of his life in East Africa, some of his views are sure to cause consternation among academic researchers on human evolution; but in Kingdon we find a primate who is unafraid to give the establishment a good hard shake, and whose keen powers of observation and reasoning make him impossible to summarily dismiss.
Kingdon thinks that the higher primates (the monkeys and apes) originated in Africa, since fossils dating back 60 million years have been found in Morocco. It is with the European apes, however, that he begins outlining his hypothesis: they thrived in Europe for ten million years, with Oreopithecus the last of the line, living out its days in splendid Tuscinian isolation until at least seven million years ago—a full three million years after its European relatives had disappeared. These creatures are important to Kingdon because he traces the origin of all African apes—including ourselves—back to them; and specifically to a group of European apes that crossed a woodland-covered land bridge into Africa around ten million years ago. These errant apes, he argues, entered a continent that had lost its native ape species around four million years earlier. And indeed there is a conspicuous gap in the fossil record of apes in Africa between around thirteen and nine million years ago.
The great novelty of Kingdon’s argument concerns the habitat of these immigrant apes. If he is correct in surmising that the common ancestor of gorillas, chimps, and humans was adapted to life in relatively open habitats, it is we humans (whose evolutionary history was largely played out on savannas) that have retained the ancestral preference for open spaces. The gorilla, then, must be an early branch of the family that retreated into the rainforest, probably as a result of climate change. The chimps also retreated from more open habitats into the dense forests, Kingdon argues, but this he sees as the result of competition with their ever more successful upright cousins.
What is most disturbing about this powerful new hypothesis is that implicit at its heart is the remarkable notion that human beings—as the only surviving open country ape—are primitive in many aspects of their anatomy. Although counterintuitive, it helps to explain why almost the entire ancient fossil record of apes in Africa documents only species that lived in open country. It also reveals the remarkable new seven-million-year-old ape fossil from Chad, Sahelanthropus tchadensis, in a new light. Known only from a skull, it resembles humans and other upright apes in its short face, small molars, and short canines that show signs of wear at the tip. The term “lowly origin” began to take on a whole new meaning when the implications of Kingdon’s masterful thesis dawned on me, for indeed our anatomy is a strange amalgam of the primitive and the highly novel. Indeed perhaps we are a lowly ape that made good.
What of Kingdon’s promise to reveal the “when, where and why” of standing and walking? Here the fossil record lets the researcher down, for it preserves no remains documenting the transition. This forces Kingdon to support his hypothesis with the assistance of an imagined creature that he dubs the East African ground ape. Kingdon suggests that it first evolved in the forest littoral zone of East Africa between six and eight million years ago. Today this zone has been almost entirely destroyed by agriculture, but enough remains to allow speculation about the creature’s habitat. It was, Kingdon thinks, a benign, perhaps seasonally deciduous environment in which the hypothetical ape gained its sustenance by gleaning from the forest floor while squatting—a posture that led to the evolution of a straight back, rebalanced head, and modified pelvis. “That these changes could improve balance on two legs,” Kingdon writes, “would have been an almost accidental bonus, an anatomical by-product.” In summarizing his thinking on how this ape first stood upright, Kingdon asserts that “reconstructions that depict hominids in bent postures are as misleading as the [famously faked] Piltdown jaw, because fully erect posture preceded bipedal gait.” In other words, the squatting ground ape had only to straighten its legs in order to put it head and shoulders above its relatives.
Whatever the course of hominid evolution between six and eight million years ago, it is clear that some apes were standing upright by the end of this time. The newly discovered chimp-sized “Millennium ancestor” Orrorin tugenensis, from the East African Rift Valley, is the oldest such creature known, dating from just over six million years ago, and henceforth the fossil record reveals more and more kinds of upright ape. Indeed to some researchers there is an puzzling abundance of them.
From this point on, Kingdon interprets the increasingly complex and well-documented hominid fossil record as resulting from independent evolution in various African river basins. His book reveals a variety of species, from the heavy-jawed “nut-crackers” such as Paranthropus boisei to more delicate beings such as Lucy (Praeanthropus afarensis). Kingdon subscribes to the minority view (first advanced by Raymond Dart in 1925) that it is the South African Man-ape (Australopithecus africanus), rather than Lucy, which lies on the direct evolutionary line leading to human beings. These southern apes, he suggests, moved seasonally from the mountains to the seaside, as do many species inhabiting southernmost Africa today. Perhaps these creatures, Kingdon speculates, were the first of our ancestors to scavenge from carcasses—a stage in our evolution that many believe was a vital step toward hunting.
It’s at the dawn of our own genus, Homo, that Kingdon’s narrative falters. This is not owing to a lack of insight, but to the great uncertainty that exists in defining our genus, and in determining which of several possible lineages was in fact ancestral to our own. The great Louis B. Leakey argued that the hallmark of Homo is the making of stone tools; yet, as Kingdon points out, this is hard to discern in practice. If a paleontologist discovers a chipped rock, how is he or she to determine whether it is a tool or a naturally fractured stone? And if the bones of several upright ape species are present in the same deposit as a supposed tool, how are we to know which ape—if any—is responsible for making it? An enlarged brain and small teeth may be better indicators of close relations to humans, but these changes are gradual and inevitably one is forced to divide a continuum.
What is clear is that around 1.8 million years ago a group of upright apes left Africa and colonized much of Eurasia. They were the first of their kind to be seen north of Africa since Oreopithecus in Tuscany, and their success in spreading so far has long puzzled scientists. It was the taming of fire, Kingdon suggests, that gave these early kinds of Homo (among them Homo erectus of Peking Man fame) the ability to spread so far into cold or otherwise hostile habitats. And perhaps their ability to control fire modified great swathes of the world, assisting the spread of grassland at the expense of other vegetation. The earliest member of this group, known as Homo ergaster or “handy man,” is thought by Kingdon to have evolved in the Atlas Mountains of northwest Africa. Like many views Kingdon expresses, this is likely to be contentious. Indeed so packed with novel ideas is Lowly Origin that it presents us with a picture of human evolution quite unlike anything that has come before it.
The British Academy has devoted its celebratory centenary volume to elucidating the origin of our own species. The Speciation of Modern Homo sapiens is a collation of specialist contributions from a remarkably diverse range of disciplines, including paleontology, archaeology, linguistics, psychiatry, neurology, and molecular biology. Ably edited by Tim Crow of Oxford University, it concentrates specifically on the role played by language in the evolution of humans.
One point that emerges forcefully from the volume is that the origin of our species has been surprisingly under-researched, and the team put together by the academy seems to have made some fundamental breakthroughs. Carole Sargent and her group examine the hypothesis that the genetic mutations allowing humanity to acquire language lie in the sex chromosomes. Crow argues that a single mutation (of an X-Y homologous gene known as protocadherinXY), located on the sex chromosomes, may have caused our species to arise almost instantaneously around 300,000 years ago. The gene in question seems to have the capacity to influence symmetry in the brain.
“Handedness”—whether we are left- or right-handed—is a convenient indicator of the development of the brain asymmetries that are thought to be required for language. Crow bolsters his case that our uniqueness as a species is the product of the protocadherinXY gene by arguing that the nature of cerebral asymmetry in humans is not only unique but demonstrably under genetic control.
The archaeologists Chris Stringer and Paul Mellars attempt to test Crow’s hypothesis by reference to stones and bones. The story they have to tell is truly surprising, for their studies reveal very little evidence for a quantum leap in the lineage leading to humanity. Instead we find more riddles and dilemmas. Mellars points out that it is becoming clear that our African ancestors had a thoroughly modern anatomy by at least 150,000 years ago, and that they had developed a “modern” upper Palaeolithic tool kit including knives by 80,000 years ago. He also finds evidence for a modern kind of people inhabiting the Levant as long as 100,000 years ago. Clearly, getting out of Africa via the Red Sea corridor was not a great difficulty for our ancestors, so why did they not spread widely in Eurasia until 60,000 years ago? By the time they arrived in Europe 40,000 years ago their technology seems not to have improved significantly at all, so we cannot look to that kind of innovation for answers. What, one is impelled to ask, were they doing dawdling away down there on the African savanna, with tools and brain power sufficient to take over the world, yet seemingly achieving nothing?
The linguist Derek Bickerton paints an even more surprising picture, speculating that although our ancestors may have acquired the vital facility of language as long as two million years ago, as far as we can discern from the archeological record they did little with it for a very long time. The brains of Neanderthals were actually larger than our own, but there is little in the archaeological debris they bequeathed to us to indicate that they used them to develop lasting art or other cultural “achievements.” Perhaps, Bickerton speculates, language and large Neanderthal brains evolved for reasons that are difficult to fathom at this remove and have little to do with their contemporary use. Bickerton gestures somewhat weakly in the direction of “reciprocal altruism” as the driving force behind the development of language, arguing that perhaps the “protolanguage of long ago was used to keep track of favors granted….” “Lo and behold,” he writes,
a unique set of circumstances provided one brand of primate with symbolic utterances, some of which described actions (verbs) and some of which described the kind of entities that might be agents, goals or themes of these actions (nouns).
One of the most remarkable discoveries of the late twentieth century is that hidden within our bodies lies a detailed journal of the travels of our ancestors. That diary is written in our genes, and its language is one of mutations—the tiny “errors” that occur when our DNA copies itself in the process leading to the creation of new life. By studying the nature and geographic distribution of these mutations, geneticists can determine the order in which they occurred as well as the geographic region of our planet where they first arose. They have also discovered that our genetic diary comes complete with a “molecular clock,” allowing them to establish an approximate time frame for the mutations, and thus our forebears’ wanderings.
In The Journey of Man, Spencer Wells interprets a great deal of detailed genetic research for a popular audience. His title is apposite, for he concentrates on genetic history as it is revealed by studies of the male-defining Y chromosome. One might wonder why—since such studies can reveal a picture of the early wanderings of only half of humanity—any researcher would so restrict himself. The answer lies in the peculiar nature of the Y chromosome. Most of it does not recombine when sperm and egg meet, as do the other chromosomes, and thus its mutations are easier to interpret. Furthermore, around 40 percent of those mutations relate to that brief period since humans began to exhibit regional variation—“race,” in the old parlance. Elsewhere in the genome such variation is rare.
One of the most significant revelations from these studies is that all men today are descended from a father who lived in Africa around 60,000 years ago. This genetic Adam, Wells deduces, was probably dark-skinned, reasonably tall, slender, and possessed of an epicanthic fold—the fold over the corner of the eye commonly seen today in people from Asia. To read the hidden genetic diaries of women, researchers must turn to another technique. Mitochondria are tiny structures that act as powerhouses for our cells. Although we could not survive without them, they are not, in a sense, part of us; they originated from ancient bacteria that took up living in the cells of our ancestors billions of years ago. This means that they have their own distinctive DNA, and because there are no mitochondria in the sperm head, their DNA is passed on solely from mother to daughter. The tale told by mitochondria largely complements that told by the Y chromosome, but there is one startling difference. Mitochondrial DNA tells us that all females alive today can trace their ancestry back to a woman, colloquially known as Eve, who lived in Africa around 150,000 years ago. Adam (who lived 60,000 years ago) and Eve, it seems, never met, and as Wells indicates, here lies a very great enigma.
Other DNA lineages must have existed long before this genetic Adam and Eve, for our ancestry can be traced back to the spark of life itself. Yet all such lineages have been lost from these parts of our human genome. Knowing this, we can deduce that the reason our genetic Adam and Eve never met is that men, as a group, have been losing genetic lineages three times faster than women.
The rate at which lineages are lost from a population depends very much on that population’s size. We might reason that men and women exist in roughly equal numbers; but it is the size of the breeding population that really counts, and the population of breeding men, it seems, has been small relative to that of women. This is probably so because a relatively small, privileged group of men has monopolized most breeding.2
Wells recounts with admirable clarity the story of human migrations as told in the Y chromosome. Africa, it seems, has repeatedly acted as a fountainhead for us and our kind. Recent studies of DNA recovered from the bones of Neanderthals indicate that their ancestors arose out of Africa half a million years ago, thereafter flowing northward around the Mediterranean, colonizing Europe. Then, 50,000 years ago, our species, Homo sapiens, began to spread across Eurasia. We know this because the Y chromosome reveals that somewhere north of the Red Sea a man was born who bore a mutation known as M130. This man has descendants across southern and eastern Asia, as well as Australia. Wells postulates that these people were coastal dwellers adapted to harvesting marine resources. The peopling of inland Eurasia, and eventually much of the Americas, was accomplished by a people whose males bore a mutation known as M89. This mutation also arose in Africa, arguing for another dispersal from our ancient homeland. Once they reached the Middle East, these people, who were adapted to truly continental conditions, gave rise to a further mutation known as M9, and then to three separate lineages that went on to settle central Asia, Europe, and India. Each of these lineages possesses its own unique marker on the Y chromosome.
Thus far in the story, all human migrations can be traced back to Africa, yet no group had managed to reinvade that continent from elsewhere. The development of agriculture, it seems, changed all that. Over the last ten thousand years the genes of the agricultural innovators, along with their languages and cultures, have spread—sometimes separately and sometimes in tandem—across the entire globe. Today, just as we have found a way to read the secret diaries of our genes, that spread has morphed into globalization. Human movements have now become so frenetic that the story told in our genetic diaries will, Wells fears, shortly become unreadable. This is because a few centuries from now, human populations may be so mixed that all traces of their ancestral wanderings will become hopelessly blended and muddled. And in view of our record for mistreating those who appear to be different, this may not be an entirely bad thing.
The Journey of Man is a book that should be read, for undeniably the story Wells reveals will transform our understanding of ourselves. Yet it includes a few peccadilloes that I cannot pass by, for they do injury to honorable people. James Cook did not consider the people of Hawaii to be primitive,3 and the native Austronesian speakers of Taiwan will be surprised to discover that they are extinct. The Australian medical establishment will, furthermore, surely be scandalized by the assertion that “horrendous medical experiments [were] inflicted on the Australian Aborigines in the mid-twentieth century”—a lie as insulting as it is untrue.
The Journey of Man is less than fully satisfying in other, more general ways. If a great historian or archaeologist could address them, the flows of human history that the genetic map lays before us could form the basis of one of the most exciting human stories ever told—and perhaps one day it will. Wells is first and foremost a population geneticist and biotechnician, so it is entirely understandable that his account of the migrations of people across the globe reads rather more like moves on a chessboard than the complex human epic it doubtless was.
Taken together, the three books under review provide a portrait of the evolution of our lineage in unrivaled clarity and detail, from the moment our earliest placental ancestors appeared in the fossil record 130 million years ago to the Neolithic revolution. Such are the recent advances in molecular biology, paleontology, and imagination that many of the insights they grant us were unthinkable just a few years ago. Yet the strange little Oreopithecus and a hundred other mysteries remain to remind us that we have a very long way to go indeed before we can master the intricacies of our evolutionary past.
September 25, 2003
For more on the evolutionary relationships and environment of Oreopithecus see J. Agustí and M. Antón, Mammoths, Sabertooths, and Hominids: 65 Million Years of Mammalian Evolution in Europe (Columbia University Press, 2002). ↩
The exact reasons why some males left many more offspring than others remains uncertain. Death of young males in a battle, polygamous mating systems (allowing a man to take multiple wives), or female choice (perhaps involving marital infidelity) are just some of the possible explanations for such an outcome. ↩
Writing after Cook’s death, and seeming to reflect the consensus view of the officers, Captain King recorded in the official account of the expedition: “Their natural capacity seems, in no respect, below the common standard of mankind”; see James Cook and James King, A Voyage to the Pacific Ocean (London: Strahan and Nicol, 1784), Vol. 3, p. 131. ↩