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Scientists have long envisioned the human “family tree” as a straight-line progression from the apelike australopithecines to the enigmatic Homo habilis to the famous Neanderthals, culminating in us, Homo sapiens. But this model is unlike the evolutionary patterns known for all other vertebrates—patterns that typically reveal multiple branchings and extinctions. In Extinct Humans, Ian Tattersall and Jeffrey Schwartz present convincing evidence that many distinct species of humans have existed during the history of the hominid family, often simultaneously. Furthermore, these species may have contributed to one another’s extinction. Who were these different human species? Which are direct ancestors to us? And, the most profound question of all, why is there only a single human species alive on Earth now?
[The Path to Human Evolution]
Almost every week or two, so it seems, there's a piece in the news about a new discovery of a fossil human relative, such as the species Australopithecus garhi from Ethiopia that is currently being touted as the ultimate ancestor of the modern human lineage. Or a new piece of information on an already known human fossil, such as our discovery of previously undescribed features within the nasal cavity of Neanderthals, or the extracting and analyzing of DNA from the fossil bones of the first described Neanderthal skeleton. Perhaps the oddest recent pronouncement was the attribution of the distinctive cranial and skeletal anatomies of Neanderthals to maladies of the thyroid gland producing cretinism. Who knows what stories tomorrow's popular media will bring?
Although we take being bombarded with this kind of information for granted—almost as if we expect it along with our morning coffee—the path followed by human evolutionary scholarship over the past century and more has not been a smooth one. Indeed, it has been fraught with problems from the very beginning—problems that persist as the field doggedly pursues the fleshing-out of our evolutionary past. The influence of the dead hand of tradition can perhaps be seen most dramatically in that many contemporary specialists in human evolution continue—whether they realize it or not—to be influenced by the work of earlier scholars who were not themselves evolutionists. To understand where we are today involves knowing where we were yesterday, solet's begin by looking at the development of ideas about humanity's place in nature.
In the Beginning
We find the first recorded musings about how the natural world works and how humans might fit into it in the writings of Greek and early Roman scholars. Common to many of these intellectuals was an interest in how the environment might affect how people look and behave. In this pursuit Herodotus (484-425 BC), who is best remembered as the first historian, made comparisons between the skulls of Persian and Egyptian soldiers killed in battle. He was impressed by how easily, so it seemed, the head of a Persian could be cracked in contrast to an Egyptian's. Perhaps, he speculated, this was because Persians were in the habit of wearing felt hats, which made the bone of their skulls thin and brittle. In contrast, Egyptian males had shaved heads throughout their lives. Could it be that their thicker cranial bones derived somehow from the constant exposure of their heads to the sun?
Hippocrates (b. c. 460BC), the acknowledged father of medicine, and Aristotle, that all-around naturalist and philosopher, also subscribed to an environmental explanation for the existence of differences among individuals living in different places and climates. Hippocrates thought that it was a damp and cold climate that made the Scythians of Asia Minor the "ruddy race" he portrayed in his writings. Aristotle (b. 384BC) picked up on this environmental theme and threw in another feature of the Scythians (and, while he was at it, of the neighboring Thracians, as well)—their straight hair—as being caused by the inhospitable climate in which they lived. In contrast to these groups, Aristotle's "Aethiopians" (from the Greek Ethiop, meaning "burned face") had woolly hair and dark, sun-burnt skin.
But Aristotle went further than merely speculating on why humans from different parts of the known world looked or acted differently from one another. As the first comparative anatomist on record, he was interested in trying to find out how the world and life on it fit together. In pursuit of answers to this conundrum, Aristotle came up with a scheme of grouping organisms that not only triumphed in his day but that dominated biological thought for almost two millennia.
As Aristotle saw it, life emerged from the inanimate. From this beginning, he conceived of a hierarchy of life (which has become better known in the Latin of medieval scholars as the Scala Naturae) that was planted at one end in an inorganic source, such as the sludge on the floor of a swamp, from which it ascended to its other end. Humans sat on the upper rungs of this Scala Naturae. Plants and non-human animal life forms were distributed among the other rungs of this ladder in a hierarchy of increasing complexity that linked the lowly inorganic with humans, the most perfected forms of life on Earth. Aristotle thought that some organisms just popped out of thin air (by spontaneous generation, as this notion would later be called), whereas others emerged from mud or fecal matter. Humans and those animals we call mammals and birds, however, either started out in life as larvae, or developed from eggs.
Although science would have to wait nearly two thousand years until the Swedish botanist Linnaeus (Carl von Linné) (1707-1778) would create the taxonomic group that we refer to as Mammalia (he called them Quadrupedia), Aristotle had succeeded in sorting out many of the fundamental features of this aggregate of animals. Starting at the broadest level, Aristotle identified those animals we call mammals as four-legged animals that both had true blood coursing through their veins and gave birth to live young. Now, he could have included birds in this group, because, as he rightfully acknowledged, birds are technically quadrupedal or four-footed animals. As he would have put it, just like mammals, birds locomote via four "points." And, again like mammals, birds are true blooded. But birds do not give birth to live young. To Aristotle, that meant that birds belong to one group, and mammals to another, within the larger group to which birds and mammals both belong.
In Aristotle's eyes, humans are like mammals and birds in having true blood coursing through their veins. Additionally, humans are similar to mammals because they give birth to live young. Superficially, humans are also like birds in walking only on two legs. In contrast to birds, however, in which the forelimbs are in the form of wings and are the individual's primary means of getting about, the arms and hands of a human are freed of this locomotory obligation. Aristotle thought that humans also differ from birds, and from all mammals for that matter, in the direction in which their knee joint flexes. He mistakenly believed that this joint bends backward in birds and mammals and forward in humans. On the basis of this seemingly profound difference, Aristotle singled out humans from other animals and proclaimed that their bipedalism reflected divinity both in their nature and in their essence. Aristotle's anatomical misconception stayed on the books until the fifteenth century, when Leonardo da Vinci finally pointed out that the joint that Aristotle had mistaken for the knee in birds and non-human mammals was really their ankle joint. That is why the joint Aristotle took to be the knee of a bird bends backward. The real knee of a bird, which, like a humans, bends forward, is hidden under the feathers up against the body. To make his point, Leonardo pictured a human standing on tiptoe. In this pose, the ankle is up and points back, just like Aristotle's birds' "knees."
Thanks to Aristotle—the orientation of the knee joint notwithstanding—bipedalism early on took center stage among the most diagnostic criteria used by comparative anatomists, and later by paleoanthropologists, to distinguish humans from other living animals. To this character Aristotle added the ability to think and reason. As attributes of the large human brain, these features put this organ also at or near the top of the list of features separating humans from the rest of the animal world. Furthermore, these two attributes—bipedalism and braininess—were assumed to be correlated. According to Aristotle, no animal could be bipedal if its body was top-heavy; with a large and heavy trunk and forelimbs, an animal just could not stand. And, he believed, weight just plain interferes with intellect and common sense. Centuries later, philosophers such as Rousseau and Lord Monboddo would wrestle with the question of whether any other animals, particularly among the apes, had the human capacities of intellect and reason. And centuries later again, with the discovery of human fossils, the debate over which feature evolved first—bipedalism or the enlarged, thinking brain—would witness vicious intellectual battles.
Indeed, the early twentieth-century Piltdown forgery, which put together a modern human skull with an apelike jaw, was evidently concocted as a direct counter to the Homo erectus fossils found in Java at the end of the nineteenth century that consisted of a modern human-looking femur and a "pithecoid" skull cap. The Javanese specimens seemed to suggest that bipedalism evolved first, whereas the fraud—despite the absence of the rest of the skeleton—was taken as demonstrating the possession of a large brain prior to the conversion of the rest of the body from ape to human. We'll never really know the reasons for the Piltdown forgery, as we'll never really know who fabricated it. But a reasonable speculation is that it would have ensured England's place as yielding the world's oldest fossil human. And, because its skull looked more human than "Java Man," and because it had housed a large brain, "Piltdown Man" could more readily be embraced as a possible human ancestor. Add to this the prevailing bias that the West was civilized and the rest of the world was not, and it is not difficult to understand how the large-brained Piltdown Man could be an easy sell.
As you might well expect, scholarly interest in the emergence of "civilized" humans has had a long and also checkered history. For instance, the Greeks and early Romans wrestled with questions about the origin of their particular state of civilization. One scenario held that the history of civilization paralleled the life cycle of an individual. The best and healthiest days are in one's youth, after which one declines into old age and then death. Likewise, the heyday of healthy and vigorous human civilization had occurred in the good old days of yesteryear. Since then, everything had gone to pot, with civilization degenerating and falling into moral decay and decrepitude. Pompeii, where streets were lined with brothels, and Rome, with couples fornicating on the steps of the Senate, come to mind as examples. The alternative view of the history of human civilization was much more optimistic. It held that in the beginning, everyday life had been more primitive and simpler than today's. Over a long period of time, humans developed technology. As technology improved, so, too, did the human condition, which eventually resulted in the high level of civilization enjoyed by the Greeks and Romans. True or not, the image of Rome's place at the top of the world's greatest cities did much to inspire the Caesars' legions as they conquered most of the Mediterranean world and lands beyond the Mediterranean. The overall theme of this view of civilization was that there was a continuum of progress from primitive to advanced humans.
Of these two themes, the general idea of degeneration would be co-opted and reconfigured into their depiction of the origin of human races by eighteenth-century naturalists such as the Comte de Buffon and by the father of physical anthropology (and also, we suggest, paleoanthropology), Johann Friedrich Blumenbach. These scholars claimed that the longest continuous record of "high" civilization was to be found in Asia, and concluded that Asia was where humans must have originated. From there, humans migrated west, to the Caucasus Mountains. The Caucasians (that is, those immigrants who stayed in the region of the Caucasus) and those others who migrated into Africa became the "white" and "black" races, respectively, through a process of degeneration from the original stock. It is interesting that, in their speculations on the demise of the Neanderthals, archeologists and physical anthropologists of the twentieth century have kept alive the notion of an invasion from the East of an overpowering, more sophisticated "race" of humans.
But it would be the theme of progress that would later pervade evolutionary thought. On a grand level, the acceptance of the reality of evolution at first had little impact on perceptions of how life was arranged. The comparative anatomists and taxonomists of the Dark Ages had kept alive Aristotle's Scala Naturae by infusing it with a Christian creation motif. This produced a taxonomic hierarchy of life's forms with humans being the closest to the image of a divine creator. This arrangement of life from the supposedly lowest to highest became known as the Great Chain of Being. When evolutionary ideas were eventually infused into paleontology, the Great Chain of Being was itself transformed into an evolutionary succession of life, from the simplest to the most complex. Among vertebrates, for example, the evolutionary succession was supposed to be from fish to amphibians, to reptiles, and thence to mammals.
On a more individual level, it is noteworthy that Charles Darwin devoted the first volume of The Descent of Man entirely to a discussion of how progression had played out in human evolution. Incorporating countless comments on how primitive humans differed physically and intellectually from those more civilized, Darwin spent chapter after chapter in this work detailing how one could follow the transformation of humans from something apelike in body and mind, through the "savages" and "barbaric" humans, to the most sophisticated of the "races," the Europeans. It is not surprising that this vision of evolutionary progress was not derived from study of the fossil record. For, by 1871, when The Descent was published, little more than the original Neanderthal skull from the Feldhofer Grotto in Germany had been presented to the scientific world in publication. Thus Darwin essentially followed the precedent of the Great Chain of Being in perceiving the ascendancy of humans through a sequence of living forms that went from monkeys to apes, to the most primitive and uncivilized humans, and on up to the most advanced and civilized humans. Having established to his satisfaction that one could trace such a transformation series through living apes and humans, Darwin could turn this horizontal comparison ninety degrees and imbue it with the element of evolutionary and geological time. But there were few fossils known that could support his contention. The only potential candidates for such a human-ape ancestor were from deposits in France and were no more than a few broken jaws—which didn't help at all. Nevertheless, Darwin speculated with supreme assuredness that, were the fossils known, a similar evolutionary transformation—from monkey through ape to primitive and then civilized human—would certainly be played out.
The idea that the human condition arose from the primitive, savage, and wild—portrayed by whichever "race" or fossil qualified as representing the lowest human condition—was not novel with Darwin. There is a long history of such formations, which are epitomized in the writings of the Roman philosopher Titus Lucretius Carus (c. 99-55BC), more widely known just by his middle name. Compared with the puny Romans of his day, Lucretius' first humans were larger and had harder and stronger bodies. Unlike Romans, who depended on the comforts of civilization, these first humans—although lacking both fire and clothing—could endure any kind of environmental circumstance. Like other animals, they traveled in bands and, depending on the weather, either slept on the ground, in thickets, or in caves. They could eat anything without consequence and rarely fell ill. How much more similar to nineteenth- and early twentieth-century reconstructions of the life of early humans—not to mention modern cartoon strips such as Alley Oop—could Lucretius' account have been?
In and Out of the Dark Ages
Although the ideas of degeneration and progress in Greek and early Roman natural philosophy might seem naive to us today, they arose from within a tradition that honored scientific investigation, questioning, and individuality of thought. This was the world of Aristotle, Hippocrates, and Herodotus, among others. In this world there was also an appreciation of humans being as much a part of nature as other animals, and, like them, being subject to the whims of their surroundings, environmental or, in the case of humans, also cultural. But both the idea that nature somehow played a role in the development of each organism's attributes and a generally healthy scientific attitude toward gathering data from the real world just for the sake of learning about it were squelched by the rise of Christianity in the first and second centuries A.D. Inquiry within the confines of a monolithic church could only proceed through the acts of prayer and revelation. Personal experience and direct observation no longer counted in the assessment of what should have been a scientific problem. In fact, inquirers were often burned at the stake or drawn and quartered as a heretics and infidels. With the resulting demise of unfettered inquiry, the biblical story of creation came to be supported by the oddest of supposed forms of proof. For instance, around the turn of the seventh century, Isadore, Bishop of Seville, noted that the Latin word for man, "homo," could be derived from the Latin word "humus." Because "humus" refers to the organic part of soil, Isadore argued, there must be truth to the story of the creation of Adam from dust as presented in the Old Testament in the Book of Genesis.
Although the naturalists of the Dark Ages were intellectually stymied, their search for evidence of the work of a divine creator did fuel the desire to clarify the details of the Great Chain of Being. To be sure, the Chain was nothing more than a translation of Aristotle's Scala Naturae in which organisms were lined up from the simple to the complex. But its demonstration became the task of the comparative anatomists of the emergent Renaissance—such as the German Konrad von Gesner, the Englishman Edward Wotton, and the Italian Caesalpinus of Arezzo, all of the mid-sixteenth century—who expressed the results of their labors in taxonomies or classifications. The common desire of these naturalists was to elucidate the supposed natural order of creation for which, of course, there could be only one scheme. And they did so through the search for organisms that would close in the gaps of, and provide the missing links in, the Great Chain. For if, according to doctrine, all life forms that could have been created had been created, then discovering them was ultimately achievable. Despite this common goal, the classifications that these scholars generated as demonstration of the divine arrangement of life were often as different from one another as the taxonomists themselves. Not only was there no coordinated or agreed-upon system of classification, there was no clear sense of what the basic unit of nature was. The idea of the species, which would ultimately be seen as the basic unit of nature, was to be long in its gestation.
There was a profound consequence of trying to pigeonhole the organic world into a taxonomy demonstrating a continuum from the most primitive to the most advanced in perfection: how did one deal with the human end of the classification? In the context of a Great Chain of Being, there had to be some humans that were closer to the "brutes" than were others. And because it was necessary for a taxonomist to provide in his classification the transition or link between the apes and the rest of humanity, various human groups were put forward as being the most primitive, or brutish, of living humans. Favorites among some early taxonomists were the Hottentots or "Bushmen" (the Kalahari San), then known in Europe by little more than rumor. Even in the nineteenth century, such rationalists as Thomas Henry Huxley and Charles Darwin had their favorite "savage." For Huxley, it was the Australian Aborigine, and for Darwin, the Tierra del Fuegian. [Figure 1] From such supposedly transitional forms—the most brutish of humans—the taxonomists proceeded to line up the races as they perceived them, leading, of course, to the pinnacle of perfection, white Europeans, with males, of course,—at the top. Some taxonomists even segregated males and females hierarchically within each perceived non-European race.
Although documenting the Great Chain of Being may have been the motivating force behind the works of these early taxonomists, the implications of such a Chain were not also uniformly shared. For some taxonomists the simple, straightforward biblical creation story encompassed all life. For humans this meant that, no matter how many different races a taxonomist carved out, they all shared the same history. They were all, according to this "monogenetic" interpretation, descendants of Adam. So far, perhaps, so good. But there was a dangerous and less attractive side. The flip side of monogenesis was polygenesis; and from the polygenists' point of view, the differences between races were simply too great for all to be traceable to the same Adam. Different races, therefore, had to have arisen from different Adams.
As late as the early nineteenth century, and still in the pursuit of the Great Chain, one taxonomist, Jean Baptiste Bory St. Vincent, went so far as to recognize fifteen species of human, which he sorted into two subgenera within the genus Homo. Clearly, this is pushing the envelope of such a presumed hierarchy in nature. Even Darwin, who used the device of a transition from identifiably primitive to civilized "man" in The Descent of Man, was committed to the membership of all humans in the same species. One cannot but wonder if a latent resurgence of belief in polygenesis has not been unconsciously behind the tendency among post-World War II paleoanthropologists to keep the number of extinct hominid species to a minimum. For, by grouping ourselves and such wildly different hominids as Neanderthals and a host of other fossil humans in the same species, the differences between groups of living humans become even further diminished by comparison.
To explain further how some early taxonomists dealt with humans, one easy way in which the differences between "us" and "them" (the rest of the organic world) could be highlighted was by not classifying humans at all—despite the agreement of virtually all taxonomists that humans were anatomically similar to the other animals that Linnaeus would eventually classify in Primates. This is precisely what the sixteenth-century Swiss comparative anatomist and taxonomist, Konrad von Gesner, did. He specifically excluded humans from his comparisons and classification. Fortunately, at least for the history of taxonomy as a discipline, Gesner did attempt to bring some order to the art of classification. He proposed the rank of genus, which he used as the base level of a classification denoting the links of the Great Chain of Being. A century and a half later, the Swedish botanist and taxonomist Linnaeus would take Gesner's genus and put it together with the species that the seventeenth-century English zoologist and comparative anatomist, John Ray, had proposed as an even more basic unit of classification. And in what would be his most radical move in the same work, his Systema Naturae, Linnaeus would place humans not only in their own genus and species, Homo sapiens, he would place them in an order together with other animals.
But it was not easy getting to the point where Linnaeus could steel himself against the calumny of his colleagues and the church by classifying humans with other animals. First there had to be a scientific recognition that humans were even like other animals. In 1632, Joannes Jonstonus took the taxonomic bull by the horns and discussed humans simply in comparison with other animals. But even this was pushing the limit of what was considered acceptable. So Jonstonus stopped there, refraining from classifying humans with other animals. He kept them by themselves, as would be expected of a view of creation in which humans were ultimately regarded as being inextricably different from other forms of life. When all else was considered, humans would seemingly always have to be set apart from the rest of the animal world because of their ability to reason and in their possession of language. Alas, revelation, not personal observation, still governed the pursuit of organismic science. Still, by this point humans were at least more visibly part of the general concern of taxonomists.
Although John Ray is acknowledged today as father of the science of systematic zoology, even he could not break free of the stranglehold of the Great Chain of Being. The place of humans as closest to their creator continued to dominate Ray's conceptions no matter how clear it was becoming that, anatomically at least, humans were like other animals—especially the apes and monkeys. By virtue of their ability to reason and their possession of language, humans would, for Ray, always be apart from their near look-alikes, monkeys and apes. It is thus something of an odd irony that Ray was the first taxonomist to recognize formally in his classification the great similarities between humans and that subset of other animals we now refer to as primates. He did so by introducing the term Anthropomorpha, which means "man shaped." But, no matter how anthropomorphic apes and monkeys obviously were, they were fated to be classified apart from humans.
Perhaps it was because of his weddedness to the doctrine of the Great Chain of Being that Ray took that one step that no other taxonomist had done previously. He went below Gesner's genus to the level of the species, a term he coined to designate the most fundamental units of life. Until Ray, even Gesner's genus was at best only a vague referent to a collection of specimens that might not even constitute a real group in nature. But Ray's species, derived as it was from the Latin word referring to a particular "kind" of something, was meant to identify true groups of individuals. Here, then, was a way to reflect the most fundamental acts of creation, to identify the kinds of animals that a divine creator had placed on the face of the earth. Species, not odd collections of organisms or single individuals displaying pathological conditions, were the real and fundamental units of nature. Although he eventually broke intellectual ranks with the taxonomists who were enslaved by the Great Chain of Being, Linnaeus would draw both on Ray's species and Gesner's genus to create the basic elements of the classification system we still use today.
A botanist by training, Linnaeus, like all good taxonomists, embraced and feverishly studied all specimens that came his way—from the inorganic to the organic, animal as well as plant. In 1735, at the ripe old age of twenty-five, this Swede became the first taxonomist formally to put humans and other animals in the same group. In the first edition of his major work, Systema Naturae, he placed humans in a group whose name he borrowed from Ray—Anthropomorpha. It was not until the tenth edition of the Systema, which was published in 1758, that Linnaeus replaced Anthropomorpha with the name Primates, the "chiefs of creation."
The broad impact of Linnaeus' work on taxonomy in general came, however, from his recruitment of Gesner's genus and Ray's species into formal usage. Under Linnaeus' scheme, every individual organism had to be assigned to a species, and every species had to be assigned in turn to a genus. The attractiveness of this formulation, and probably a major reason for its rapid and wide adoption, lay in Linnaeus' demand that each species and each genus be defined on the basis of at least one tangible feature or trait. Until Ray introduced the concept of the species and Linnaeus formalized its usage, taxonomists were not bound by any common rules. But, under Linnaeus's scheme, the description of each species conveyed the details that made that particular organism distinct from all others.
If there were some number of species that appeared to have some features in common that suggested that they, in turn, constituted a natural group, then they were placed together in the genus, which was defined on the features that these species shared that were not specific to each as a species. The genus was then defined on the basis of a next higher order of information. Linnaeus did this with what he thought consitituted different species of humanlike animals, including the orangutan, which he lumped with our own species in the genus Homo. And if it appeared that several genera (the plural of genus) shared certain features, then they would be grouped into a higher taxonomic rank, which would be defined on the basis of this still higher order of information. What were you supposed to do if a species appeared to stand alone? According to Linnaeus, it still had to have a genus name, but, in this case, the genus and species shared the same definition. But if a genus came to subsume more than one species, its definition was based on those unique features common to all of its species.
By following Linnaeus' rules of classification, taxonomists could know the criterion or criteria that another taxonomist had used in creating, for example, a new genus or new species. They would also then be able to decide if an unclassified specimen should be allocated to a known genus or species or if it deserved to be distinguished in its own, new species or a new genus and species. In the Systema of 1758, Linnaeus' Order Primates came to embrace the genera Homo, Simia, and Lemur. The genus Lemur subsumed the "lower" primates and Simia included monkeys but not apes because the two apes that were then known to science, the orangutan of southeast Asia and the chimpanzee of central Africa, were classified as species of Homo. Although Linnaeus labored to define each genus and its species by at least one anatomical feature that seemed to be distinctive of it, he did not do so for Homo. Homo was simply defined by the phrase Nosce te ipsum, know thyself. Apparently, if. Linnaeus had been totally free of the religious and political shackles of his day, he probably would not have created a separate genus for humans. As he admitted in a letter to a colleague, he did not believe that any feature of note separated Homo from Simia. He did so only to minimize the amount of opprobrium he would attract with his brazen act of classifying humans in a group with other animals. Although the phrase Nosce te ipsum may have been useful advice in a philosophical sense, it was to be of no help whatsoever when it came to dealing with the fossil record.
Putting Humans into Evolution and Fossils into Human Evolution
Although evidence has always existed of the presence of different kinds of past humans, its significance was long in being recognized and was misinterpreted well into the Renaissance. For instance, large megalithic structures, such as Stonehenge, were thought to have been the work of giants of superhuman strength who had once roamed the face of Earth. Stone artifacts, which were exposed along river banks or uncovered when fields were plowed or foundations for roads or houses were dug, were interpreted in one of two ways: either they came from the heavens (the smaller projectile points and arrowheads often being referred to as "elf arrows" and the larger implements as "thunderstones") or they were formed in the bowels of Earth, just like any rock or stone. Konrad von Gesner coined the term ceraunia for such objects. Not only would ceraunia come to embrace a cornucopia of geological objects, it would subsume all excavated hard objects. Thus, ceraunia come to include stone artifacts that had been modified by humans, as well as fossils, which are bones and teeth that become rocklike through the process of mineralization. For centuries fossils, stone tools, and everything else geological were often illustrated in the same plates by one scientist or another who lumped them all together as "things that had been dug up."
The odd thing is that, by the sixteenth century, Europeans were aware of the existence of humans elsewhere in the world who actually used stone instead of metal tools. However, only the sixteenth-century Italian Renaissance scholar Michele Mercati made the proper connection. Before the end of that century, he had suggested that people in the past had also made stone tools, and that such implements were represented among the ceraunia that were being discovered. Unfortunately, Mercati's treatise, although possibly read by some of his contemporaries while in manuscript, was not published until the eighteenth century. Thus the class of ceraunia began to unravel only in the second half of the seventeenth century, with the demonstration by the Danish geologist and anatomist Nicholaus Steno that the structure of rocks that were identical with clams and mussels or shark's teeth were not rocks at all. Instead, Steno explained, these objects had the detailed features of the shells of living clams and mussels or sharks teeth precisely because they were the remains of living organisms that were simply contained in rocks as they formed. [Figure 2]
With the realization that there had actually been ancient organisms whose remains had been incorporated into the rock record, you might think that the stage had been set for the acceptance of human antiquity. And indeed, in 1686, the English natural historian Robert Plot became the first to publish a work on the manufacture of stone tools by earlier humans. He even illustrated stone tools in the same plates as seventeenth-century implements, toys, sculpture, and monuments. There was now no turning back. Stone tools from the past had become an accepted reality.
But there was a downside to this recognition. Another English natural historian, John Woodward, had emphatically stated in 1728 that if you made stone tools, you were not only technologically unsophisticated, you were nothing more than a barbarian and savage. Stone tools that were dug up in the fields had to have been made by earlier humans, who, of course, had been barbaric and savage compared with eighteenth-century Englishmen. But the course of human history had been away from the barbaric to the civilized, away from stone tools to the advanced technology of metallurgy. Truly civilized humans of the eighteenth century had followed this path of progress. The consequence of adhering to this simple-minded chain of thought, however, was that if you were to find any living humans who still made stone tools, they had to be savages. And, unfortunately, western European explorers had discovered many groups of people who still used stone and other non-metal tools. If you belonged to a western society, this simple dichotomy—metal-tool use equals civilized, non-metal tool use equals savage—gave justification to conquest and subjugation. If you were the "other," you were out of luck. As we saw, even Charles Darwin was not exempt from these temptations.
Despite scientists' acknowledgment of the reality of fossils and stone tools, and of the implications from stone tools uncovered in the fields that there had been earlier primitive humans, only non-human animals were allowed by Scripture to be older than the general time of the Great Flood. This was because, if you followed the sequence of creation, nonhuman animals preceded humans. Because animals still inhabited Earth, obviously fossils of now extinct animals not only represented the historical sequence of creation, they also reflected the reality of the biblical flood that had killed off those unfortunate enough not to be saved by Noah. Humans, however, had been created last and in the image of God. Since the period of the Great Flood began with Adam and Eve, humans—primitive or not—would not have existed earlier in time. Thus, in 1857, when Schaaffhausen and Fuhlrott became the first to publish on a fossil human, the evident antiquity of this important specimen—the famous Feldhofer Grotto Neanderthal—was far from universally accepted. [Figure 3]
|Chapter 1||The Path to Human Evolution||13|
|In the Beginning|
|In and Out of the Dark Ages|
|Putting Humans into Evolution and Fossils into Human Evolution|
|The Evolutionary Synthesis: Exempting Humans from Natural Selection|
|Chapter 2||Evolution Today||43|
|Chapter 3||Early Bipeds: African Origins||55|
|The New Era|
|Not Another Australopith! And Another?|
|The Age of Discovery|
|The Making of the Hominid|
|What to Do with Australopiths?|
|Chapter 4||The Mysterious Homo habilis||105|
|Back to Olduvai|
|Unraveling Homo habilis|
|The Influence of Climate|
|Chapter 5||The Emergence of the Modern Body||125|
|East Side Story|
|When East Meets Far East|
|Another East African Homo erectus?|
|A Glimpse at the Life History of the Nariokotome Youth|
|Will the Real Homo erectus Please Stand Up?|
|Chapter 6||Homo ergaster and Homo erectus: The Great Diaspora||147|
|The Cave of Zhoukoudian|
|The Invasion of Europe|
|Chapter 7||Neanderthals and Human Extinctions||173|
|The Ice Age Environment in Europe and Western Asia|
|Neanderthal Burial and Symbolic Behaviors|
|Chapter 8||And Then there Was One||223|
|Out of Africa|
|The First Modern Europeans|
Barnes & Noble.com Science & Nature editor Laura Wood conducted this interview with Dr. Ian Tattersall in his offices at the American Museum of Natural History.
Barnes & Noble.com: When I was carrying the book in the elevator, people did a double-take when they saw the title Extinct Humans.
Ian Tattersall: I've heard different viewpoints on it; it's a very grabbing title. There are many books out on human evolution, but I don't think any of them has such a direct title.
B&N.com: I think it gets across your main theory -- the recognition that there have been a lot of species of hominids, which includes modern humans and other members of the genus Homo and related species. I don't believe the general public realizes that, although there's more awareness now with so much written on the Neanderthals. But when I tell people that there were more than a dozen, they are amazed. What do you think that the popular impression is?
IT: Just as textbooks are always ten years behind the times, I think public understanding of science is probably more behind the times than that because received wisdom is a very powerful thing. And the received wisdom is that human evolution was linear -- sort of a simple-minded slog from benightedness to enlightenment and that it was basically just one species doing this slog through time, getting better and better. Even though we would call it by a number of different names, it was just one lineage.
B&N.com: The impression that's given is that one species is morphing into the next one -- not that they were separate species that actually went extinct.
IT: Exactly. People think of the stages of human evolution as progressing into the next one in a linear fashion. And that's not what happened at all. The message we are trying to get through to people is that the evolutionary history of humans, as for just about any other kind of organism that we can study the fossil history of, has been one of evolutionary experimentation leading to a natural triage of species. So new species are produced; they do whatever they do; they are successful or not successful; they disappear or not.
B&N.com: Or they are unlucky.
IT: That's right. They can just be in the wrong place at the wrong time.
B&N.com: I sometimes like to say that it's not really the "survival of the fittest" but the "survival of the survivors." I don't know where I picked that up, but the point is that the finest specimen can get buried under an avalanche by chance or die in any accident.
IT: Well, that's a very important perception that you have because we think of evolution as a process of fine-tuning, generation by generation. However, that's not accurate. Most of the time, nothing much is happening, and chance plays a great role in who is successful and who isn't. The environment is constantly changing around species. Fine-tuning doesn't get you anywhere if your environment suddenly changes. People have this received wisdom that our ancestors have been simply striving toward a well-defined goal over millions of years. It's very hard to imagine how, in a dramatically changing and fluctuating world, a lineage of hominids could have proceeded single-mindedly toward a particular goal over millions and millions of years. It just doesn't coincide with anything that we really know. So the notion of ecological experimentation -- of a pruning of the evolutionary bush -- makes more sense to people when they think about it.
B&N.com: I wanted you to give an example of what it really means to have different species of hominids in the same landscape, all together. For example, with the big cats, you might have lions and cheetahs living in the same landscape together. Is that the sort of image people should have of these different species that are in the same landscape -- perhaps interacting, perhaps not interacting.
IT: That's a very good question. In fact, because when we think of ourselves as being special, what is misleading is to look at other kinds of humans, earlier kinds of humans, as sort of junior-league versions of ourselves. That's not at all what they were. And modern humans are very intolerant of their close relatives in nature. We did away with other human species and now we're busy doing away with our nearest and dearest right now -- chimpanzees and gorillas and orangutans. On the other hand, that's not necessarily true of our predecessors. I'll give you an example. Nowadays, there are forests in Africa and South America where you can find half a dozen closely related species of monkey -- all existing together and getting along perfectly well and doing business in their own way. And who knows if this would be a better analogy for the early humans 2 million years ago when there were at least four human species on the same landscape. Maybe they just got along by basically ignoring each other or even having peaceful interactions with each other. We just don't know.
B&N.com: I suppose there would be some indication...perhaps simply the number of years that they are both in existence in the fossil record at the same time, not to get too much into conjecture.
IT: We really don't know what the longevity of any of these species was. We don't know when they began. We don't know when they ended. All we know is that in some place in time they existed. We know the fossil record is incomplete in terms of the entire historical span. So it's very difficult to know precisely. In the old days when bunches of fossils were thrown together in catch-all categories like Homo erectus, you could talk about a million years -- or now you would have to talk about 2 million years -- when Homo erectus was around. But these species don't all look the same.
B&N.com: Tell us a little about this project you're working on -- reclassifying human fossils. How long have you been working on it?
IT: It's been six years at this point. If you go to the literature today you find that everyone is describing these fossils according to their own standards and it's very difficult to make comparisons from one study to the next to know exactly what people are talking about. What we are trying to do is create a single protocol, which will allow us to describe as many fossils as we can in a single format within which comparisons can be made.
B&N.com: And that entails going back and looking at the actual fossils again.
IT: Absolutely, you have to look at the original fossils. Because only original fossils have the level of detail that you need to make these descriptions full. Even though humans have been around for over 2 million years, they are a very small, closely-knit group. So the differences between them are detailed differences, not ones of large scale construction, and that difference you can only see on original specimens.
B&N.com: What in particular is there about this book that you think that a general reader would be intrigued by?
IT: This book tackles basically two areas. The first is where do humans fit into nature. We are one of many different species. All species are nature's experiments. Readers can learn from this book that we are but one experiment in a long series of experiments that have been going on for millions of years. And that places us metaphorically within this great bush of nature. Instead of being at the top of an evolutionary tree with our ancestors simply providing the trunk, we now use the metaphor of a bush to get across the actual variety in nature. And the other is a look at the process of speciation; the process of becoming human and what happens along the way. So you have two aspects: a big pattern of nature that is laid out where we identify where humans fit into the pattern and then this process, the historical reality of becoming human. I think these two aspects as being and becoming. So anybody reading this book is going to get a pretty good impression by the end of it of what the evidence is and how that evidence is interpreted.
B&N.com: Is there something changing in the zeitgeist that has allowed people to have this more complex view of our own origins?
IT: There are two things that happened. There was the discovery of many more fossils -- an augmentation of the fossil record so you've got more basic data to deal with -- and then you have new ways of looking at those data and formulating hypotheses about what happened. In my professional lifetime, the human fossil record has expanded by a factor of three at least and at the same time people have been asking themselves what are we doing about these fossils. Are we just joining them up in straight lines and recording them on stratigraphic charts and sort of joining up the dots, or are we looking at the systems of relationships that need to be analyzed?
B&N.com: You mentioned cladistics in the book. It's a new conceptual tool for organizing the fossil record by creating diagrams that show the most recent common ancestor between species, which was originally used to clarify relationships between nonhuman species. We like to think that human evolution was an exception, but the theoretical tools were in place that allowed this revision to take place at this moment.
IT: That's true. Put both of those together and you come up with a very different picture than the previous one. Before, evolution was viewed as a kind of jigsaw puzzle. You didn't have the picture on the box, but you put every fossil you found in a slot and that would be part of the picture. Now we are dynamically changing our perspective and the same fossil doesn't just sit in its slotted place, but can be reinterpreted over and over again. In science all knowledge is provisional.
B&N.com: Am I remembering correctly that now you think there may be around 17 different species of humans in the fossil record?
IT: Seventeen is the number you get if you add up all the species on the cladogram. I got an email from China saying, "I'd heard that you believe that there's 17 species." I had to think a moment and go back to my chart and see that that's precisely what I did. Yet it's not outlandish. We're talking millions of years, 5 million years, so 17 species may not be that many.
B&N.com: For comparison, how many species of primates are there?
IT: Depending on whom you believe, it's 250 or thereabouts. That's how many there are today.
B&N.com: Not that have ever existed.
B&N.com: When you start looking at it that way then, 17 doesn't seem so big. But there was still a big evolutionary leap to get to modern humans.
IT: How that leap was achieved is up to question. I think the prime leap with humans was a cultural, not a biological, leap. It was so recent that it's almost inconceivable that huge populations of biologically archaic humans were replaced in a very short amount of time. It's much more likely that whatever the stimulus was for modern consciousness and behavior, it was something that could be absorbed by all humans by cultural contact.
B&N.com: Right. The biology would allow it, but didn't necessarily cause it in the sense that it arose as soon as anatomically modern Homo sapiens came on the scene. There was a time lag before humans had symbolic expression, such as the cave art at Lascaux. They already must have had the physical capacity, but that capacity had to wait until some breakthrough in thought came along. In the book, you speculate that the stimulus was the invention of language. Someone or some group came up with the idea. It spread rapidly, and shortly afterwards all the other hominids died off.
IT: Well, yeah. There's something in that, unfortunately.
Posted November 25, 2001
This is the best - bar none - book on paleoanthropology I, a layman in this field, have ever read. It is not only complete in the sense of covering all the relevant fossils, it also covers the ways the different fossils, and thus the species concerned, differ from each other. That is not a common thing in books written to be read by scientist and layman alike. (Either the author is a scientist and displays the fullness of his knowledge without due regard, or he is a layman who skims it, and either way you are left feeling unsatisfied. So I have found.) I found it enjoyable, enlightening, and also highly useful.Was this review helpful? Yes NoThank you for your feedback. Report this reviewThank you, this review has been flagged.