EVOLUTION OF THE GENUS HOMO
31 DECEMBER, ABOUT 10:30 PM; ABOUT 999,818 METERS UP THE LINE
Only now, in the last hour and a half of our one-year Universe, can we begin to examine the branch of life that led directly to the modern humans. Only now, after having considered (if only very briefly) the whole story of space-time and energy-matter’s origins and evolution, can we look for our specific place in the tumultuous story of reality. We have traced the (at least) 60 million-year evolution of the primates. We have noted in particular how the ardipithecines and the australopithecines evolved in eastern, southern, and perhaps central Africa, and how their upright posture lent a crucial survival advantage to them. Are we their descendants, or is our true lineage yet to be uncovered? We will weigh the various ideas of those who are attempting to find that nexus between non-human and human, the point—perhaps impossible to define—at which distinct members of our genus stood in the African sun for the first time. What traits, if human only in rudimentary form at first, did they possess? From what lineage did the first animals that everyone acknowledges were genuine humans, Homo erectus, emerge and how did they bring forth our particular species and subspecies? In examining all of this and how it unfolded, we must bear in mind an inescapable fact: over all these developments the processes of natural selection and genetic drift reigned, indifferent and without the capacity for remorse or intent.
Attempting to Define the Boundary Between Non-Human and Human
In general, in our examination of the evolution of the primate line, we have seen the following trends or tendencies in particular:
1. A significant increase, over millions of years, in the average size of primates. In particular, with the evolution of the family Hominidae, there was now a lineage of primates that produced animals of more substantial height and weight than the average monkey, even when modern mandrills and baboons are taken into consideration.
2. The increasing ability of certain of these larger animals to function both in trees and on the ground, an ability facilitated by the evolution of bipedalism. This bipedal capability probably began to emerge when the ability to stand upright while in an arboreal setting proved to be adaptively advantageous. What was useful in the trees proved to be even more so on the ground. Hominids tended to retain significant climbing abilities and the ability to move through branches along with this ability to live on the ground.
3. An increase in the ability to reach, manipulate, and transport objects, a direct consequence of the ability to stand upright for increasing periods of time and the freeing of the forelimbs from use in locomotion. This tendency favored the evolution of hands good at examining, manipulating, and using objects to facilitate survival.
4. A general increase, in Hominidae, in the average brain size, and just as significantly, a change, in certain lineages, in the average brain shape. These changes were indicative of animals with an increasing ability to use fluid intelligence—intelligence that is brought to bear in processing information and the solving of novel problems—to meet the challenges of existence. Such intelligence allows certain animals to notice objects in the environment and conceive of novel uses for them. Those animals that evolved brains not just of large absolute size and large size relative to the rest of the body, but configured and organized in particular ways, had a tremendous advantage over animals that did not possess such brains. In connection with this, we must note something that we have not touched on before: intelligence gives an animal that is not particularly strong, fast, or agile in comparison to its predators behavioral options. It does not have to rely on a single strategy to cope with deadly threats. It can run or it can hide or it can fight or, most crucially, it can live in social groups capable of organized defense, a defense which can include the use of objects as weapons. Primates evolved a tendency toward social living, perhaps very long ago. Now, intelligence and social living in combination proved to be tremendously useful from a survival standpoint.
5. The retention, in many members of Hominidae, of primate tendencies toward omnivorousness, and the evolution of dentition that reinforced and facilitated these tendencies. Omnivores have obvious survival advantages, and their ability to ingest other animals and obtain nourishment from the protein of those animals was a significant factor in their ability to flourish.
So one would think that the task of identifying a set of traits particular to humans would be a fairly straightforward one. But such is not the case. Few problems have been more difficult in the area of paleoanthropology than defining the boundary line between human and non-human. In 1964 the great paleoanthropologist Louis Leakey and his colleagues Philip Tobias and John Napier said that an animal that possessed all of the following traits was a human: a physical structure that permitted habitual upright posture and bipedalism, arms shorter than legs, a hand with a fully opposable thumb capable of precision grip, a facial structure distinct from that of the typical australopithecine, a rounded dental arch and smaller premolars and molars than the australopithecines, and the possession of a brain at least 600cc in capacity.1 Certain brain sizes have often been thought of as the “Rubicon” beyond which an animal was definitely one of our genus, and Leakey’s definition of the minimal human brain size is probably one of the smallest ones in the literature. The 600cc figure seems to have been chosen specifically so that Homo habilis, which Leakey’s team had both discovered and designated, would be included in our genus. Other researchers considering the location of the boundary line have included the fashioning of tools into the mix along with the other criteria. For several decades, a view much like Leakey’s tended to prevail in anthropology and paleontology.
In 1994 Richard Leakey, Louis’s son, and a prominent paleoanthropologist in his own right, offered an unusually broad view of the term human. Leakey said that since they were capable of upright locomotion—the key development, in his opinion, in our evolution—all hominids should be considered human. Leakey stressed that this did not mean that ancient hominids saw the world in the same mental way in which we do. Leakey’s definition would stretch the human line back 7 million years, by his calculation (the point at which, at that time, the split between hominids and ancestral chimpanzees was thought to have taken place).2 It must be said that while there are some researchers who have defined the word human in a similarly expansive way, most seem to apply more restrictive criteria.
Recent discoveries have raised new issues in regard to the boundary between human and non-human. If Australopithecus garhi or A. sediba were able to use objects as primitive tools, if they were capable of true bipedalism, if they had, in many respects, human-style dentition and dental arches, if they had flexible hands capable of precision grip, and if the largest of their brains (not the average ones) crossed Louis Leakey’s 600cc “Rubicon”, how finely do we have to draw the line to distinguish ourselves from the more human-like australopithecines? Is the idea of a cerebral “Rubicon” a valid one? Does the crucial criterion boil down to the humerofemoral index? Is relative finger length where we draw the line?
Two specialists in human evolution, Mark Collard and Bernard Wood, believe that any species we wish to place in the genus Homo must meet the following criteria:
… for an extinct hominid species to be allocated to the genus Homo, two conditions must be met. First, cladistic analyses should indicate that the species is more closely related to the type species of Homo, H. sapiens, than it is to the type species of Ardipithecus, Australopithecus, Kenyanthropus, and Paranthropus. [This is to say that the animal must clearly show evidence that it is not a member of one of the possible ancestral or sister clades to Homo.] Second, the body mass and shape, the inferred locomotion, the rate and pattern of hard tissue development, and the relative size of the masticatory apparatus of the candidate species should be more similar to the strategies used by the type species of Homo than they are to the type species of the other early hominid genera listed above.3
By the term strategies in the passage above Collard and Wood mean adaptive strategies. An adaptive strategy is that set of traits that allows a species to survive and reproduce. For example, the kind of animal that engages in obligate bipedalism is using a different strategy than one adapted for both walking and arboreality. Adaptive strategies exist within an adaptive zone, a particular kind of environmental setting that influences the adaptations of the life forms within it. An adaptive zone is not simply a place. It is a way of living within a place, the methods by which an animal exploits, and survives within, a particular environment. It is within an adaptive zone that the interplay of genetic variability and environmental influence takes place. Several different kinds of animal taxa in a given adaptive zone (which may be thought of as ecological niche) may have similar adaptive strategies. An adaptive zone provides opportunities for evolutionary changes and often tends to produce phenotypes (body forms and structures) that are similar across many taxa. Animal lineages that occupy a range of diverse settings and become adapted to them by selection are undergoing adaptive radiation. (In a sense, the entire biosphere of this planet is a shifting collection of adaptive zones, emerging and disappearing in an irregular way over time.) Did the first purported humans live within adaptive zones characteristic of those occupied by primates we know to be part of Homo? This is part of what paleontologists are looking for when they compare different varieties of human-like primates. The question they want answered goes beyond, “How was this animal built”? They also want to know, “how did this animal survive and make a living?”
Criteria for Inclusion in the Genus Homo
So after considering all of the arguments above, what defines a human? A primate can be considered a member of Homo only if all of the following criteria are met:
--The estimated volume of the cranium is greater than that of the average australopithecine or modern great ape. Naturally, scientists use cranial capacity to estimate brain size. The definition of what constitutes the minimum human brain size is still a matter of great debate. Many paleoanthropologists are reluctant to consider animals with an estimated 600-650cc cranial volume humans. They feel more comfortable when the cranial volume is at least in the 750-800cc range. With fossil remains, measuring cranial capacity can be problematic, inasmuch as many of the specimens examined have missing, partial, or damaged cranial bones. Further, the cranium contains more than the brain. It also contains the meninges, three layers of membrane that protect the brain, and this factor has to be taken into account when doing estimates. The relationship of brain size to body mass is significant as well. If researchers do not possess adequate post-cranial specimens, ascertaining this ratio in a particular primate can be a matter of great difficulty, or even an impossibility. Moreover, the sheer size of a brain cannot always tell us much about its organizational structure. We cannot, for example, infer the possession of language skills by examining the endocranium, the skull’s inner surface, despite the assertions of some researchers in the past. (In regard to the brain’s internal organization, the shape of the cranial vault can give us clues, but no more than that.) Human cranial capacity indicates, broadly, an animal of sufficient intelligence to survive in a variety of settings.
--The animal must be a true obligate biped, one that moves most efficiently by bipedal walking on the ground to the exclusion of knuckle-walking, quadrupedal movement, or methods of moving through branches, such as brachiation. This bipedalism must be demonstrated by the position of the foramen magnum, distinct pelvic and vertebral structures, the angle of the femur, the structure of the knee, the arch of the feet, the anatomy of the tarsal bones, and the positioning of the big toes. The gait of the walk revealed by these traits must be characteristically human as well. In short, the locomotory apparatus must indicate an animal that made or makes its living in a terrestrial setting.
--The animal must possess a forelimb structure distinct from that of the australopithecines or great apes. The humerofemoral index is around 100 in the modern great apes, meaning simply that their arms tend to be as long as their legs. In modern humans, the index is around 70. The animal must have a hand structure that exhibits recognizably human morphology, i.e. fingers suited for prehension, but not of the kind of length in relation to the thumb characteristic of chimpanzees or gorillas. The thumb must be large and fully opposable, suitable for both a precision grip and a power grip (the ability to wrap the fingers and thumb around an object). In short, the arms and hands of the animal must allow it to exploit the environment by examining and manipulating objects within the recognized human range of ability.
--The animal must possess molars and premolars smaller than the huge vegetation-crushing teeth of australopithecines and certain great apes. It also has to have canines less prominent than those of the other hominids as well. The dental arch must be (approximately) in the form of a parabola. The dentition must indicate an animal fully able to exploit a variety of potential food sources in the environment.
--The structure of the face and cranium must be distinct. Specifically, the jaw must not be as prognathic (jutting out from the rest of the face) as that of the apes. The supraorbital torus (or brow ridge) must be less prominent than in the apes or australopithecines. The zygomatic arch, running from the maxilla to the temporal bone and including as its main section the cheek bone, must be relatively less prominent as well. The calvaria (skullcap) must be distinct from the other hominids, meaning there must be no pronounced sagittal crest at the apex of the skull, the forehead which forms its anterior section must be distinct (in some respect) from that of an australopithecine, and the endocranial volume must fall within recognized human limits. (See above.)
As you see, I am using many of the criteria proposed by Louis Leakey and his colleagues while agreeing with the critics of those criteria that the minimum human brain size is probably significantly greater than that postulated by Leakey. I think we would be on safe ground in regarding any primate that exhibited all of the features listed above as a human. Naturally, specific traits can exhibit a great range of variation from individual to individual.
What are the criteria we cannot use, and what knowledge will we never possess?
--We cannot define humans by the phrase, “those who made the first tools”. There is strong evidence, as we have seen, of tool use or tool fashioning, albeit very crude, in some of the later species of australopithecines. As we will see, it was the incredible elaboration and development of tool use that set humans apart from other animals, not tool use itself.
--We cannot say that social living defines humans either, as those who have observed troops of chimpanzees or baboons could tell us. It is the great complexity of human social life that sets us apart, not the basic fact of group interaction.
--Finally, we do not know the point at which genuine human consciousness emerged. It is likely that consciousness existed on a continuum in the evolving primate order. The point on that continuum at which the characteristic human way of seeing the world first manifested itself can never be known. Our attempts to infer this by assessing brain size and shape will always be educated guesses, and our definition of the minimum human brain size will always be to some extent arbitrary.
Competing Views of Human Phylogeny
Paleoanthropologists have produced numerous cladograms that offer hypotheses about the line of descent leading from the late Miocene apes to Homo sapiens. For all their diversity, these charts do tend to have certain views or assumptions in common:
1. They agree that, in order, the apes that split off from the lineage leading to humans were the gibbons, orangutans, gorillas, and chimpanzees.
2. Most agree that the genus Homo is monophyletic.
3. They agree that the genus Paranthropus was a side branch and an evolutionary dead end.
4. They agree that the first undoubted member of Homo was Homo erectus.
Additionally, as we saw in the previous chapter, a rough chronology of primate evolution is beginning to emerge, thanks to back-breaking field work and pains-taking, exhaustive analysis in the laboratory. To recapitulate, here is the chronological sequence again:
Sahelanthropus tschadensis, 6 million to 7 million ybp.
Orrorin tugenensis, 6 million ybp.
Ardipithecus kadabba, 5.5 to 5.8 million ybp.
Ardipithecus ramidus, 4.4 million ybp.
Australopithecus anamensis, 4.2 to 3.9 million ybp.
Australopithecus afarensis, 3.7 million (perhaps) to 3.0 million ybp.
Kenyanthropus platyops (disputed taxon), 3.5 million ybp.
Australopithecus bahrelghazali (disputed taxon), 3.5 million to 3.0 million ybp.
Australopithecus africanus, 3.0 million (perhaps) to 2.3 million ybp.
Australopithecus garhi, 2.5 million ybp.
Australopithecus sediba, 1.95 million to 1.78 million
Genus Paranthropus (three identified species), 2.7 million to 1 million ybp.
As I also stated in the last chapter, simply because we have established a chronology, it does not, by necessity, mean that every animal in it has a phylogenetic relationship to the others, and paleoanthropologists are very careful to point that out in their research. There are, as we saw, highly interesting similarities among the various species, but it is, as yet, not possible to establish an unassailable, definitive lineage that leads from the Miocene (much less the late Oligocene) primates to us.
Having said this, therefore, what are the major points at issue in tracing our phylogeny?
WHAT WAS THE RELATIONSHIP OF THE AUSTRALOPITHECINES TO HOMO?
As we saw in the previous chapter, there are paleoanthropologists who reject the notion that Homo emerged out of the australopithecines, hypothesizing instead that the australopithecines and humans stemmed from a common ancestor and went their separate ways. Kenyanthropus platyops has been proposed as a direct ancestor to humans, for example. Some scientists contend that the ability of even the latter australopiths to live in an arboreal environment casts doubt on their role in the rise of the committed terrestrial bipedal genus Homo. But it must be said that the majority of researchers are convinced that humans did indeed evolve out of one line of these upright animals. There seem to be no other credible candidates—yet.
A great many cladograms have been constructed over the years offering hypotheses about the phylogeny of our genus in general and the relationship between australopithecines and humans in particular. To cite only a few examples, in 2005, before the discovery of A. sediba, paleoanthropologist Roger Lewin presented, in his standard text on human evolution, four different hypotheses offered by different researchers concerning the phylogenetic relationship of various finds to us. In all four of the hypotheses, Ar. Ramidus lies at the base of the phylogenetic tree (although one of the groups of paleoanthropologists constructing these trees puts a question mark next to ramidus). All of them postulate that A. anamensis is descended from ramidus. All of them postulate that afarensis (or in one case, what are called simply the specimens found at Hadar and Laetoli) is descended from anamensis.
But after that, there are sharp differences of opinion. In one scenario, the animals the remains of which were found at Hadar and Laetoli lead to P. robustus and P. boisei, while some of the Hadar animals might have a relationship to africanus. In another scenario, afarensis splits, one group evolving into boisei, another into africanus. Another hypothesis is that afarensis splits and on one hand produces all of the genus Paranthropus and on the other evolves into africanus. In the first three hypotheses, it is africanus that gives rise to Homo. The fourth scenario is more intriguing. The scientists constructing it have left room for three different unknown species. One of these unknowns is descended from afarensis and gives rise to P. aethiopicus in one direction and africanus in another. Africanus gives rise to a second unknown species, that splits in two directions. One product of the second unknown is a third unknown. The third unknown produces robustus and boisei. The other product of the second unknown is Homo.4 Many other phylogenetic schemes have been offered over the years, and new finds invariably alter our ideas. (In the notes for this chapter, I have incorporated links to a number of different cladograms to allow the reader to see the variety of hypotheses that have been presented.)5
As of this writing (2012), the two strongest contenders for the line directly ancestral to Homo are A. garhi and A. sediba, whose traits we have already examined. If A. garhi ultimately turns out to be our ancestor, this will mean our genus probably had an east African beginning. If it was A. sediba, then the human race was probably born in southern Africa. But there is another possibility: that our genus was not monophyletic. Indeed, multiple lineages of humans may have evolved separately, and the lineages we have found that were contemporaneous with each other (if not necessarily living in proximity to one another) may have been the product of this polyphyletic origin. Certain evidence seems to point in that direction. It also may be that we have yet to uncover our direct ancestor. There is yet another factor we must admit is possible: that the animals once considered to be the first humans, Homo habilis and Homo rudolfensis were, in fact, particularly distinct forms of australopithecine. (See below)
In my view, the major issues are those of brain size/shape/organization/relation to body size. Complete obligate bipedalism is crucial in defining a human, yes, but it is the ability to comprehend the world (to some degree, at least) that to my mind separates a very bright non-human from a not-so-bright human. Where is the line between the two? No one can say. Was the very bright non-human standing on one side of that line the product of an australopithecine lineage? There is no consensus either way. But what can be said is that there was a significant increase in brain size in certain hominin lineages, and this becomes detectable in specimens dating back to about 2.5 million to 2.0 million ybp. The only bipedal primates we know of from that time are the australopithecines A. africanus and A. garhi and the purported members of Homo, Homo habilis and Homo rudolfensis. Further, the first stone tools, as we will see, date from somewhere around 2.6 million to perhaps 2.5 million ybp. No genus of upright animal other than Australopithecus or Homo has ever been associated with them. The ability to conceive of using objects found in the environment to extend the body’s ability to do work, or to modify objects found in the environment to do work, is indicative of a brain that is physiologically complex. What change in the brain’s neurochemical organization might be associated with this increased mental sophistication? A team of researchers may have found a possible answer.
In humans, sialic acid, specifically N-acetylneuraminic acid (abbreviated as Neu5Ac), is found in the greatest concentrations in the brain, where it plays a significant role in building synapses and facilitating “signaling” between neurons.6 Humans are unable to synthesize a different kind of sialic acid, common to all other mammals, known as N-glycolylneuraminic acid (abbreviated as Neu5Gc). A mutation that affected our genome rendered the gene responsible for Neu5Gc’s production inactive. It is thought that this mutation occurred after the split between the ancestral chimpanzees and the hominins and well before the evolution of modern humans. Studies of Neanderthal specimens have detected Neu5Ac but not Neu5Gc. This means the mutation that blocks the synthesis of the latter acid must have happened before the emergence of the common ancestor of Neanderthals and us. After taking the Neanderthal data into consideration and comparing our genome to that of the great apes, the research team investigating this issue estimated that the key mutation occurred between 2.8 million and 2.7 million ybp—just before the great increase in encephalization (the ratio of brain size to body size) among certain hominins. The researchers caution that it would be premature to ascribe the increase in hominin encephalization to the absence of Neu5Gc in humans, since the brains of other mammals retain relatively low levels of it (while possessing greater amounts in other organs). Still, it is a suggestive phenomenon.7 Current techniques make sialic acids difficult to detect in fossil specimens in the 2 million year-old range or greater. But if it can ever be demonstrated that Neu5Gc was absent in the later australopithecines while Neu5Ac was present, that might be a powerful argument in favor of a phylogenetic relationship between Australopithecus and Homo.
WHAT WAS THE ROLE OF THE EARLIEST PURPORTED MEMBERS OF HOMO?
Although it was not designated as H. habilis at the time, the first fossil example of this species was discovered in 1959 by the Leakey research team. The specimens came from the Olduvai Gorge of Tanzania, and that area rapidly became the epicenter of research on human origins. It was in Leakey’s research paper announcing habilis that he and his colleagues set forth the criteria by which Homo is defined. Homo habilis (the name literally means “Handy Man”) has generally been accepted as the first true human, but there are increasing doubts about its place in our phylogeny (see below).
Specimens attributed to habilis have been discovered not only at Olduvai Gorge (from which several examples have been extracted) but also at Koobi Fora (also known as East Turkana) in Kenya, Uraha, in Malawi, Omo and Hadar in Ethiopia, and Sterkfontein and Swartkrans in South Africa.8 (The hominids/hominins that existed after the ardipithecines are designated in the following way: AL meaning Afar Locality, Omo meaning Omo, Ethiopia, OH meaning Olduvai Hominid, KNM meaning Kenya National Museums, SK meaning Swartkrans, South Africa, or Sts or Stw meaning Sterkfontein, South Africa). Chronologically, the earliest appearance of habilis (and the possible related species, Homo rudolfensis) is difficult to ascertain. Three distinguished experts in paleoanthropology and primatology have concluded that, on the basis of very fragmentary remains, the earliest examples of habilis/rudolfensis may go back as far as 2.4-2.3 million ybp. They also point out, however, that the fossil record from 3.0-2.0 million ybp is very sketchy, and that little is known of the environmental conditions in which the first members of Homo evolved. Further, they note that around 1.8-1.7 million ybp there were perhaps three different species of Homo—habilis, rudolfensis, and erectus—living at the same time, and that it is not yet possible to establish firm phylogenetic relationships among them. 9
Several problems arise when we try to describe habilis in a satisfyingly consistent way. First, there is the fragmentary nature of the actual specimens. There have been more than 30 separate discoveries of habilis remains, but only KNM-ER 1805 (dated to 1.7 million ybp), KNM-ER 1813 (dated to 1.9 million ybp), OH-13, OH-16, OH-24, SK-847 and Stw-53 are significant parts of the cranium, sometimes including sections of the maxilla and the dentition. Post-cranial fragments from other finds consist of some femurs, a couple of humeri, a hip, a partial foot, and a number of small skeletal fragments, including some parts of the hand. Chronologically, all specimens date from about 2.3 million ybp to about 1.5 million ybp (although ranges of estimates for certain specimens vary widely).10 So although we possess a relatively large number of specimens, they are not comprehensive in nature by any means.
Second, habilis-like remains display a considerable range of diversity, which was why the species rudolfensis was originally designated. In cranial capacity, habilis remains have ranged from about 500cc to 700cc [and some researchers put the upper range higher].11 This diversity is further illustrated by the work of one scientist studying the brain-body ratio (and dietary habits) of early members of Homo. She has pointed out that there appears to be what she describes as “substantial overlap between larger specimens of H. habilis…and smaller specimens of H. erectus”.12 Still, the idea that habilis was a single species that showed a normal range of variation has its defenders. A group of researchers carefully analyzed variations in habilis-like cranial specimens KNM-ER 1470 [often classified as rudolfensis], KNM-ER 1813, OH-24, and Stw-53. They then analyzed the range of variation in gorilla skulls. Their conclusion: “Craniofacial variation in early Homo…is not excessive as previously claimed when compared to gorillas.” They stress that the degree of sexual dimorphism in habilis has not yet been firmly established, which might affect the interpretation of the finds.13 It must be said, however, that the bulk of scientific opinion seems to be moving toward the opinion that habilis-like specimens are best thought of as being part of at least two species.14
Third, habilis specimens sometimes display an unusual mosaic of traits, some of them quite australopith-like in nature. The cranium designated KNM-ER 1813, cited above, is an example of this. The specimen was discovered at Koobi Fora and dates from 1.9 million ybp. The cranial capacity is only about 510cc, which seemingly puts it in the australopithecine range. (The modest cranial capacity is not because the animal was a juvenile. Analysis of the teeth indicates it was an adult.) Yet the facial features and dentition are unlike those of the australopithecines.15 Further, although habilis specimens give strong evidence of bipedal capability, they also indicate that this primate retained a strong climbing ability, meaning that it was probably a facultative biped (an animal capable of walking on two feet but not necessarily doing so as its normal mode of locomotion).
Detailed analysis of OH-62 (a large set of fragments that includes post-cranial material) has uncovered further evidence of the somewhat primitive nature of habilis. The specimens, dated at 1.8 million ybp, were probably from an adult female, only about 36 inches in height, with hands that reached her knees. The morphology of the hand bones appears to be similar to that of an australopithecine. The anatomical gap between this specimen and erectus appears to be significant. Some researchers looking at this evidence have concluded that habilis was simply not advanced enough to be considered a part of Homo. As one put it, “Homo habilis remains more of an evolutionary idea than an example of anatomical fact linking one species to another.”16
Homo rudolfensis is similarly problematic. The first specimen that is now usually considered to be part of the species was discovered by the Leakey research team in 1972, but the designation rudolfensis [from Lake Turkana’s previous name, Lake Rudolf] was not suggested until 1986. The chief differences between habilis and rudolfensis are all craniodental, inasmuch as there are no post-cranial remains associated with any rudolfensis cranium. The most significant specimen is KNM-ER 1470, a very complete cranium and maxilla. The brain size is estimated at 775cc. It has been dated at 1.8 million ybp. It is distinct from habilis in its supraorbital torus, its facial dimensions, the shape of the maxilla, and indications that it must have possessed large post-canine teeth.17 The only other significant craniums or cranial fragments of rudolfensis are KNM-ER 3732, which consists of the calvaria and part of the zygomatic arch, and KNM-ER 3891 which contains, among other pieces, fragments of the cranial vault, parietal bone, and palate.18
Habilis has been associated with very simple tools, those of the Oldowan tradition or the Oldowan mode. The first Oldowan tools to be discovered, at Olduvai Gorge, were hammer-stones and cutting instruments called flake tools. Bifacial tools (rocks modified on both sides) came somewhat later. It is thought that rudolfensis must have been a tool user, but as yet no tools can be definitely associated with it.19 Most Oldowan tools appear to fall into the 2.0-1.5 million ybp timeframe, although older examples have been identified. It appears, however, that the oldest stone tools, discovered at Gona, in the Afar region of Ethiopia, predate habilis, with estimated dates of 2.5 million to 2.6 million ybp ascribed to them. These tools are, according to some researchers, attributable to Australopithecus garhi. Since the tools found at Gona stretch chronologically from about 2.6 million to 1.5 million ybp, they may be part of the broader Oldowan tradition. Their significance is potentially very great. From a principal researcher of the area:
Late Pliocene hominids began manufacturing and utilizing ﬂaked stones c. 2·6 Ma, and the Gona localities provide the earliest evidence of a high density of stone artefacts… The beginning of the use of modiﬁed stones was a major technological breakthrough which opened windows of opportunities for eﬀective exploitation of available food resources including high nutrient meat
Naturally, this scientist points out, chronologically older finds may point to a more gradual technological evolution. But the implication is clear: habilis and rudolfensis may have been the inheritors of the Oldowan tradition, not its main creators. Other researchers note that non-human primates, especially chimpanzees, use objects from the environment as tools, and that A. africanus and A. afarensis may have had brains of a size comparable to chimpanzees, and hence may have had similar tool-using capabilities. Further, the features of the hand in africanus, afarensis, (as well as habilis) may all have been suited for the use and modification of objects in the environment, and not only ones made of stone. Bone tools from both southern and eastern Africa, dating from 2.0 to 1.5 million ybp, have been found, and there is also evidence that wood may have been used for tools at that time as well. 21
There are scientists who argue that habilis and rudolfensis belong together in a separate genus, although this would complicate our picture of hominid phylogeny. Alternatively, it has been suggested that what we think of as the first two species of human are actually better thought of as Australopithecus habilis and Australopithecus rudolfensis. There is as yet no consensus in the scientific community about what are sometimes called the habilines (habilis-like primates), and it will take the discovery and careful analysis of other specimens to put the various remains in their proper context. Certainly, the discovery of Australopithecus sediba has given those who doubt the human status of the habilines new arguments. The possible roles of the habilines can therefore be summarized in this way:
1. The habilines were the first members of the genus Homo, and they gave rise to erectus and hence every modern human.
2. The habilines were side branches of the genus Homo that died out, leaving no legacy.
3. The habilines were actually australopithecines and had no relationship to Homo.
4. The habilines were australopithecines that gave rise to Homo ergaster, and thus
they were the nexus between the genus Australopithecus and the genus Homo.
5. The coexistence of the habilines with erectus is due to the fact that erectus is the
product of a subpopulation of habilines that has yet to be firmly identified.
The discussion of the role of the habilines therefore is directly related to our next questions…
WHAT IS THE ORIGIN OF HOMO ERECTUS? WHAT PHYSICAL CHARACTERISTICS MADE HOMO ERECTUS DISTINCT?
The first species within Homo to be universally recognized by all researchers as an undisputed human was, as we noted at the outset of this chapter, Homo erectus, simply meaning, as one might surmise, “Upright Man”. The oldest specimen attributed to erectus is thought by some paleoanthropologists to be approximately 1.9 million years old, although its true affinity might be habilis or rudolfensis. There is more substantial evidence for erectus at 1.8 million ybp,22 and at 1.7 million ybp the specimen labeled KNM-ER 3733, a fairly complete cranium discovered at Koobi Fora, gives us very firm evidence. Its cranial capacity was 850cc.23
It is perhaps necessary here to discuss how paleoanthropologists tend to describe hominid remains. When they apply very specific and restrictive criteria to a species, they are defining it sensu stricto—that is to say, in the strictest sense of the term. Sometimes a paleoanthropologist might describe a species by the term sensu lato—in the broadest sense of the term. The application of broadly-defined criteria is often necessary, given the somewhat indistinct boundaries between species and the frequently ambiguous features of fossil specimens. A broadly defined species can also be thought of as a species that shows a mixture of “primitive” and derived traits while a species defined in the strict sense is more fully derived. So in the earliest specimens of erectus we have, we are often limited to trying to identify the species sensu lato, and new finds sometimes cause researchers to redefine what is meant by erectus sensu stricto.
The most complete example of Homo erectus, and the most complete ancient human skeleton of any kind ever found, was discovered in Kenya in 1984. Nicknamed Turkana Boy (for Lake Turkana), it is also known as Nariokotome Boy, for the specific location in which it was unearthed. Its museum designation is KNM-WT 15000. This specimen was once thought to have been a twelve year-old boy, based on the anatomy of his skull and the characteristics of his teeth. However, a recent study, incorporating new data and new analytical methods suggests that he was probably about eight years old, about 154 centimeters in height, and had probably reached over 90% of his adult height at the time of his death. This would indicate that erectus was not as tall in stature, perhaps, as we had once thought, and not as drastic a break with what had come before. Such a human would have had an adult brain in the area of 850cc. The specimen is dated at approximately 1.5 million ybp.24
Because of such specimens as KNM-ER 3733 and Turkana Boy, most scientists have reached the conclusion that erectus was of African descent. But others are now asking: Was there an Asian origin of Homo erectus? There are scientists prepared to say there was, based on the evidence gathered from several important finds at Dmanisi, in the Republic of Georgia. One researcher has argued that the evidence for an east African origin of erectus is ambiguous at best, and the Dmanisi specimens, although originally categorized as erectus, are much more similar to habilines.25 As he has put it:
… there is now a rival hypothesis to the canonical one that H. erectus originated in Africa and was the first hominin to disperse into Asia. The alternative proposition is that H. erectus originated in Asia from a population of Homo that dispersed out of Africa before 1.8 Ma; some of this Asian population of early H. erectus then dispersed back into East Africa and others dispersed eastwards to Java.26
The picture is further complicated by the contention of some researchers that the very earliest specimens of what have usually been called erectus, are in fact examples of a more primitive species known as Homo ergaster or “workman”. Ergaster was first proposed in the 1970s. It status as a separate species is argued on the basis of its distinct molars, premolars, cranium, mandible (bigger than erectus specimens), and generally more rounded head. Some scientists consider ergaster to be strictly African in heritage, while viewing the animals classified as erectus as strictly Eurasian in nature. These same scientists contend therefore that sapiens was the product of ergaster, not erectus. There are also researchers who argue that erectus evolved from ergaster, and that habilis may have given rise to ergaster.27 Moreover, despite the contention that the Dmanisi finds are habilines, other researchers have argued that most Dmanisi specimens clearly fall into the ergaster/erectus range of cranial size. Three of the crania found at Dmanisi in fact appear to contain a mixture of African ergaster and Asian erectus traits.28
Those scientists who agree that ergaster is a valid taxon generally view Turkana Boy as an example of the species. They also see KNM-ER 3733 as ergaster as well. Other significant finds that are said to fall into ergaster are KNM-ER 992, a mandible found in northern Kenya and dated at 1.5 million ybp, KNM-ER 3883, a probable adult male specimen that contains the cranial vault and some of the facial structure (including a very large zygomatic arch), discovered at Koobi Fora and also dated at 1.5 million ybp, and OH-9, from Olduvai Gorge, the upper part of a skull with a large, semi-rounded cranial vault and a prominent brow ridge.29 It should be noted, however, that there is substantial disagreement among paleoanthropologists concerning the status of OH-9. Some scientists contend that OH-9, even though recovered in Africa, resembles the Asian forms of erectus, thus making its phylogenetic status uncertain.30
The erectus/ergaster controversy is far from resolution. But whether erectus-like animals were part of one species or two, we can summarize their physical traits in the following way:
--Erectus’s cranial capacity increased significantly over time. In the earliest specimens ascribed to erectus, cranial capacities ranging from 600 to 900cc were most common, with some specimens crossing the 1000cc threshold. By the time the latest members of erectus appeared, cranial sizes of 900cc were the lower end of the scale, and most specimens exhibited cranial capacities of 1000cc or greater, with some ranging up to 1200cc. This means that the estimated brain size of late erectus overlapped with the lower ranges of brain size attributed to modern humans.
--The cranial vault itself tended to be low compared to modern humans, and the typical erectus skull was wider than it was high, in contrast to humans like us. The shape of the braincase itself was similar in certain respects to that of modern humans. The sagittal ridge (at the top of the skull) was prominent, and the nuchal torus, a thick ridge of bone in the rear of the skull, was pronounced.
--The brow ridge was prominent, the forehead sloped, the chin receding. The face was large, the mouth was somewhat prognathic, and the neck appears to have been strong. The jaw and teeth were strong as well, but noticeably more derived than those of habilis.
--The dimensions of the postcranial skeleton resembled ours in many ways. Erectus was taller than the primates that had preceded it. It was also probably stockier and more muscular than modern humans. Significantly, it seems to have exhibited a less marked degree of sexual dimorphism than earlier primates, putting it in the more modern range in this respect.31
Probable erectus/ergaster footprints have been discovered at Ileret, Kenya. They have been dated at 1.51 to 1.53 million ybp. In 2009 it was announced that these footprints strongly resemble those of modern humans, and are markedly different from the tracks at Laetoli which were apparently made by afarensis. These footprints are clearly from animals that were fully bipedal. As the researchers publishing the results put it,
The Ileret footprints show the earliest evidence of a relatively modern human–like foot with an adducted [toward the midline of the body] hallux, a medial longitudinal arch, and medial weight transfer before push-off…these modern human characteristics, in combination with the large size of the prints, are most consistent with the large size and tall stature evident in some Homo ergaster/erectus individuals. These prints add to the anatomical and archaeological evidence pointing to a major transition in human evolution with the appearance of hominins with long lower limbs, conferring advantages at a lower energetic cost, and archaeological indications of activities in a variety of ecological settings and the transport of resources over long distances.32
We do not yet know the deep origin of ergaster/erectus. Since habiline specimens dating from as recently as 1.44 million ybp have been found, and erectus-like humans and habilines apparently coexisted for hundreds of thousands of years, many scientists now argue that habilis did not give rise to erectus. The fossil record from 2 million to 3 million ybp is, as we have noted, not very complete. The ancestral group that gave rise to erectus-like animals is still not clear.33 Was it A. sediba, or an unknown habiline-like subpopulation, or A. garhi, or a line of animals that has yet to be unearthed? It is one of paleoanthropology’s major objectives to find answers to these questions.
WHEN AND WHERE DID ERECTUS RADIATE THROUGHOUT THE EASTERN HEMISPHERE?
It would appear, according to many researchers, that there were quite possibly migrations of erectus radiating from the African continent before 1.8 million ybp. Erectus got as far into southeast Asia as Indonesia. In fact, the first erectus remains were discovered by Eugene Dubois in Java, and formally described in 1894. The specimen was originally called Pithecanthropus erectus. Since that first discovery, scientists researching human origins have attempted to place all the known erectus specimens into a chronological and geographical framework. What have they ascertained?
In eastern Africa, there were ergaster/erectus types perhaps as early as 1.9 million ybp and perhaps as late as 700,000 ybp. Outside of Africa, there were erectus-like primates at Perning, on the island of Java at about 1.8 million ybp. Erectus remains have been discovered at several places in Indonesia (especially Sangiran), and there may have been relict populations of the species living in Indonesia less than 100,000 ybp. At around 1.7 million ybp, erectus-like primates were at Dmanisi. [Although this has been disputed, as we saw.] In China, erectus remains date back at least to 1.1 million ybp, and there may have been erectus living in China as late as 200,000 ybp.34 In the Middle East, evidence of hominin presence has been uncovered at Ubeidiya, Erq el Ahmar, Gesher Benot Ya`aqov, and Ruhama in Israel (among other Middle Eastern locales), and at the first three sites tools associated with erectus have been unearthed. There is substantial evidence of hominins (perhaps erectus/ergaster) in South Asia. The status of erectus in Europe is in dispute, as we will see below.
Homo erectus remains in China were first discovered at Zhoukoudian, near Beijing. Scientific excavation and analysis of these remains began in the 1920s and accelerated in the 1930s. [Unfortunately, the original specimens that were dubbed “Peking Man” by the archaeologists of the time were lost in the Second World War. Casts of the originals were preserved, however.] Significant erectus remains have been uncovered at several other Chinese sites, most notably Longgupo Cave (along the Yangtze River), Gongwangling on the Yellow River (where the oldest erectus remains in China have been discovered), and Hexian.35
Recent research indicates that erectus occupied Zhoukoudian as early as 770,000 ybp.36 Zhoukoudian specimens, which are designated by the abbreviation ZKD, have endocranial measurements ranging from 1110cc to the largest specimen, ZKD X at 1225 cc. Recently measured ZKD V came in at 1140cc. Despite their great distance from Africa, the Zhoukoudian specimens bear certain important similarities to African erectus samples, especially to the cranial morphology of KNM-ER 3733 and KNM-WT 15000.37 There are Chinese paleoanthropologists who have tried to make the case that early sapiens interbred with late erectus populations in China, but the genetic evidence does not support this contention. (See below)
Was erectus in Europe? There were most definitely human populations in Europe prior to the evolution of sapiens, but their exact identity is a matter of dispute. There is evidence from Atapuerca that there was indeed human occupation of Europe in the Early Pleistocene. The evidence is in the form of a human mandible with some dentition, a set of very primitive tools, and some animal remains that may indicate human butchering. The date of these finds, 1.2 to 1.1 million ybp, is the earliest yet established in Europe. The affinity of the human specimen is uncertain, although the scientists analyzing it suggest that it might from a species known as Homo antecessor, hypothesized by some scientists to have been a transitional species between erectus and heidelbergensis in Europe.38
WHAT APPEAR TO HAVE BEEN THE CHIEF CULTURAL TRAITS ASSOCIATED WITH ERECTUS?
A culture may be thought of, broadly, as a way of life handed down through time within a given set of humans. It is the sum of a group’s ideas and beliefs, methods of achieving objectives, and traditions, in short its learned behaviors. It is also the sum of a group’s characteristic material objects and the uses to which they are put. It is primarily conveyed by language of some sort, although it can also be acquired by imitation. We will examine the concept of culture very thoroughly in a subsequent volume, but for now it will suffice for us to say that the way of life established by the various populations of erectus had a major effect on the development of human life on this planet.
The various erectus populations of the eastern hemisphere possessed rudimentary tools that are broadly known as Acheulian. The characteristic Acheulian-style tool was the bifacial hand axe. Other known Acheulian tools included cleavers, choppers, and picks. Acheulian industry is thought to have emerged between 1.7 and 1.5 million ybp, and its typical tools seem to have made their first appearance in east Africa. Recent research indicates that Acheulian tools do not seem to have originated out of the older Oldowan tool tradition. They appear to have been, rather, a technological innovation made to accomplish a broader range of tasks than Oldowan tools. They co-existed with Oldowan tools in east Africa for about a million years.39 Three researchers who have done extensive work on ancient tools at Gona in Ethiopia have summarized the possible reasons that some scientists (mistakenly, in their view) see a transitional stage between Oldowan and Acheulian tools:
[Those who contend there was a transition] may be conflating separate cultural/technological/ecological changes occurring in the Late Pliocene/Early Pleistocene that may or may not be interconnected, such as: (1) the ability to knock off large flakes, (2) the ability to flake invasively and shape tools purposefully with predetermination or preconception of form, (3) the standardization of tool shape and/or technique, (4) changing diet and ranging patterns, (5) possible changes in group size and/or organization, and (6) possible changes in learning styles and abilities. Early Pleistocene hominins may have “experimented” with these developments initially until all elements came together in the classic Acheulian.40
It should be noted that the authors are careful to say that although Acheulian tools are usually associated with erectus/ergaster, the appearance of erectus-like primates and the earliest Acheulian tools are not contemporaneous, and may in fact be separated by more than 100,000 years.41 Still the implications of these findings are significant. Early humans, as they ranged farther and farther out into the world and encountered increasingly diverse challenges, devised technologies suitable to the tasks with which they were confronted. Moreover, these technologies may be the product of a profoundly important synergy: the coming together of higher levels of intelligence, a wider cultural tradition, and more complex modes of social life, all of which may have come together to form a self-reinforcing/self-perpetuating phenomenon.
Acheulian-style tools may have been culturally-communicated to hominins other than erectus/ergaster. One of the most thoroughly studied sites associated with the Acheulian tradition is Gesher Benot Ya`aqov (abbreviated GBY), in northern Israel. The Acheulian tradition in the Levant is a long one, stretching from 1.5 million to 200,000 ybp. Yet, owing to the sparseness of the hominin remains recovered in the area, it is difficult to say which species of humans are associated with particular finds. It is even possible that several different types of hominins coexisted in the Levant and participated in the same tool tradition. Certainly the long temporal record of human habitation there suggests it.42
But beyond the intrinsic interest the artifacts and the various animal remains found at GBY hold for us, what they infer about human cognition is of even greater interest. Naama Goren-Inbar, who has done extensive work at GBY, cites the following indicators (among others) of human cognitive abilities the site reveals to us:
--The ability to exploit biological resources. The hominins of the GBY region were able to process the carcasses of large animals, including elephants, indicating facility with large cutting and chopping devices. They were also able to exploit marine life. Such abilities are marks of people with a specialized skill-set. These abilities were also no doubt aided by the hominins’ knowledge of the habits of regional animals and an understanding of the ecology of the area’s plant life.
--The ability to use fire (see below) and the ability to organize work spaces efficiently.
--The ability to manufacture tools efficiently. This would have involved selecting suitable kinds of stone, quarrying it if necessary, judging which techniques were most suitable for tool-making, the application of technical know-how in the actual tool-making process, and the ability to teach this know-how.
--The ability to conceptualize and plan tool manufacture. These abilities infer the possession of such capacities and skills as communication, developed working and long-term memories, spatial cognition, planning, cooperation, and effective social interaction.
--The ability to innovate and the possession of creativity.43
The Levant, of course, was also part of the pathway erectus/ergaster groups took into southern, eastern, and southeastern Asia. In south Asia, Acheulian tools have been found in many locales in India, with more than 3,500 found at one Indian site, Attirampakkam, alone. Using a variety of dating techniques on the sediments in which these Acheulian artifacts were uncovered, scientists now estimate that there were hominins present in southern India before 1,070,000 ybp.44 In fact, the Indian subcontinent is a major repository of Acheulian tools, and some sites have as many bifacial tools as every Chinese Acheulian site combined. Many Indian sites are particularly rich in cleavers, and there is evidence of quarrying and organized manufacturing techniques. However, it is difficult to infer continuous human occupation of certain regions. In the Hunsgi-Baichbal Valley, [in southwestern India] for example, although there are almost 200 Acheulian sites, if it is assumed that humans lived in the area for 750,000 years that number of sites represents one site established (on average) about every 3,800 years. [Obviously, there may have been many sites that were contemporaneous.] It is not yet possible to judge the length of time humans inhabited specific sites. We can say that humans, including erectus, occupied many areas of the Indian subcontinent, but we have no reliable way of ascertaining their numbers.45
In China, the oldest large cutting tools have been found in the Bose basin, in the far south. The tools appear to be Acheulian in style and have been dated to about 800,000 ybp. However, there is not much evidence that the bifacial tool making in this region was of long duration. The tools may have been a technological response to extensive deforestation in the area. In general far fewer Acheulian-style tools (often called Mode 2 technology to distinguish them from simple, unifacial, Oldowan-style artifacts known as Mode 1 technology) have been found in east Asia than in south Asia, Europe, or Africa. The existence of a boundary called the Movius Line is sometimes used to explain this phenomenon. This line demarcates the regions of more sophisticated and less sophisticated stone tool manufacture. Although some critics contend that the Movius Line concept is outdated, it still appears to have utility. The researchers studying the Bose basin summarize their findings by saying,
Bose stone technology is thus compatible with Mode 2 of western Eurasia/Africa just before the early-middle Pleistocene boundary. This finding implies similar technical, cultural, and cognitive capabilities on both sides of the Movius Line. The flow of population and cultural information across the line, however, may not have been extensive.46
Two researchers who have investigated the Movius Line phenomenon have noted that Acheulian-style tools in east Asia not only are less abundant but tend to be cruder, less symmetrical, and less extensively worked than those found elsewhere. They summarize the various hypotheses offered to explain this:
1. There were humans living in eastern and southeastern Asia prior to the advent of Acheulian technology.
2. The raw stone materials available to east Asian toolmakers were of low quality (a hypothesis the researchers tend to dismiss)
3. The abundance of bamboo in the region allowed east Asians to use it to perform much of the work that previously had been done by stone hand axes, causing the manufacture of bifacial stone tools to be abandoned.
4. Geographic barriers such as the Himalayas kept hominin settlement in east Asia low.
5. Hominin populations in east Asia fluctuated, hindering the process of passing on
So in considering the relative rarity of Acheulian-style tools in China, Korea, and southeastern Asia we get an idea about the limits of cultural diffusion in the world of 800,000 years ago. We see perhaps the first evidence in human life of a cultural tradition’s spread being limited by such factors as physical isolation from the mainstream of human progress.
Europe, on the other hand, had a very extensive Acheulian tradition. However, it did not extend to the entire continent. Two paleoanthropologists who have devoted extensive research to this subject point out that its heaviest concentration was in southwestern Europe, and the Acheulian tradition only got as far north as about latitude 52°N. North and east of Germany and England, evidence of hand axe industry cannot be found, with the exception of a few finds in southeastern Europe. These researchers have identified 16 significant tool sites in the Iberian Peninsula, the oldest of which that can be reliably dated being Atapuerca, Orce, Barranco León, and Fuentenueva. The Atapuerca site may indicate Acheulian-style tool-making as early as 700,000 ybp. Outside of Iberia, significant finds have been made in Italy (although they indicate the sporadic nature of early human occupation in the Italian peninsula), France (including St. Acheul, from which we get the name Acheulian, and which had its characteristic tools around 400,000 ybp), and England, where numerous hand axes have been found at a variety of sites dating from as early as 400,000 ybp.48 As we will see, Boxgrove in the UK may be the earliest English Acheulian site of them all. (And humans may have occupied part of what is now England well before that.)
The issue in regard to early human settlement in Europe is this: was the Acheulian tool culture spread there by erectus—or did a successor species bring Mode 2 technology to the western end of Eurasia? We will examine that question below.
The ability to use tools facilitates the reproductive chances of those animals that possess it. It is not sufficient, of course, by itself to guarantee such success. Tool use requires the possession of a suite of intellectual capacities. These capacities combine themselves in such a way that some humans can devise technical solutions to practical difficulties. Enough members of erectus displayed such abilities to allow it to survive in a far-flung range of environments for hundreds of thousands of years.
A major human innovation is the ability to generate fire, an ability unique in the animal kingdom. (It is important, by the way, to distinguish between the use of naturally-occurring fire and the use of deliberately-created fire. The use of fire may have preceded the ability to create fire by many millennia.) Did erectus possess this ability? Most researchers tend to be cautious about dates associated with fire use. There was at one time thought to be firm evidence of fire use at Zhoukoudian at 500,000 ybp, but a detailed analysis in the late 1990s cast doubt on this. Although the site has yielded some burned bones and other indirect evidence, no ash layers or evidence of campfires can be found.49 In 2004 evidence was published that fire was used at Gesher Benot Ya`aqov. According to the researchers studying the site, humans were making fire at GBY almost 790,000 ybp, and they have ruled out natural events, such as brushfires, as the cause of the burned specimens (mostly wood) they have recovered. They are reluctant, however, to associate this apparent fire use with a specific species.50
Fire has always been regarded as having been essential to the human settlement of the northern latitudes, but the evidence seems to indicate that the human occupation of Europe may have preceded the use of fire by hundreds of thousands of years. A recent study has found that although humans reached northern Europe some 800,000 years ago, it is virtually impossible to find evidence of fire use before 400,000 ybp. As they examine the archaeological record, researchers see a great increase in the tempo of fire use in prehistoric Europe from 400,000 to 200,000 ybp as humans mastered this ability more and more. But the remarkable fact remains: there were humans inhabiting some very harsh climates for a very long time who may have lacked the ability to make fire.51
Recent research as of this writing (2012) points to strong evidence that erectus populations in Africa controlled fire as early as 1 million ybp. The evidence comes from the Wonderwerk Cave of South Africa, which has yielded a number of Acheulian hand axes. Stratum 10 of the cave gives clear indications, through deposits of ash and charred animal bones, that the hominin occupants of the cave were engaged in an activity of enormous significance: cooking. Based on an estimate of how hot the fires these hominins used were, the fuel to make these fires was apparently brush, grasses, and leaves.52 If hominins were cooking one million years ago, this may represent the start of an activity that greatly facilitated human success. Cooking chemically alters food, not only making it more palatable but also breaking down the tough fibers of meat, making the consumption of its protein content more feasible. Cooking can also chemically alter plant-based foods as well, unlocking their nutritional potential. In effect, cooking acts as a sort of external stomach that begins the process of digestion, thus making a wider range of food available for use in the human metabolic process. Not every erectus population in the world had fire, but those that did possessed a skill of great utility.
How did erectus-like animals acquire their food? Of what did their diet consist? Certainly we must assume that foraging was an important part of erectus/ergaster’s adaptive zone, and that this survival strategy was widely used. We assume, for example, that australopithecines were opportunistic feeders, gathering fruit and other vegetation wherever it could be had, and there is no reason to believe the earliest humans were any different. But the larger size of erectus-like humans, especially the larger brains they possessed, suggests to us that they must have, out of sheer necessity, widened the range of their diets fairly early in the existence of the species. [The evidence of animal bones at their campsites is telling on this point.] This wider diet would have, in turn, facilitated their physical growth, reinforcing their meat-consuming tendencies. A major climatic shift may have played a role in this meat-acquisition strategy. There seems to have been a significant reduction in forest and a concomitant expansion of grasslands at just about the time erectus/ergaster was evolving and spreading.53 The effects of all these factors were hugely significant. As the authors of a study on early hominid diets have put it:
“…primary activity in early Pleistocene Africa was substantially lower than in the Pliocene, thus limiting the edible plant foods available to hominids…However, secondary (herbivore) and tertiary (carnivore) trophic-level foods likely increased in abundance; this ecological shift would have increased the over-all mammalian biomass—especially of ungulates and other large mammals—available to hominids with the technological and cognitive abilities necessary to exploit this resource…In fact, behavioral flexibility within the context of environmental variability and ecosystem heterogeneity may have served as an important selective factor in hominid encephalization.54
The development of Acheulian-style tools would have greatly increased the ability of erectus/ergaster to process animal flesh, and organized hunting would have increased the significance—and reinforced the reproductive advantage of—such social behaviors as planning, coordination of efforts, communication, division of labor, manufacture of hunting weapons, and a system for dividing the carcasses of those animals that were killed. It is possible that erectus did not hunt all of its own meat. It may have often engaged in confrontations with, and stolen the kills of, other animals which had successfully hunted game. There is also the issue of scavenging. Several researchers have hypothesized that the scavenging of carcasses by erectus was more common than hunting. Certainly, it is reasonable, in my view, to assume that the earliest humans engaged in widespread scavenging.
Yet, it instructive to observe the hunting behavior of non-human primates, specifically baboons and chimpanzees. While we must be cautious about using the behavior of our primate relatives as a model to infer behaviors in our earliest ancestors, it is still noteworthy that baboons in west Africa have been observed engaging in surprisingly sophisticated hunting, hunting that may have been a learned behavior on the part of many of its participants. Chimpanzees hunt and consume meat with regularity, and even a New World monkey, the capuchin, is an avid hunter.55 In itself, this does not prove that our ancestors were hunters. But if primates with less intelligence than erectus are capable of effective hunting, there is no reason to believe that hunting was beyond the capacity of erectus/ergaster.
It seems likely that the first human hunters emerged before 1 million ybp. It further appears that hunting and the consumption of energy-dense, protein-rich food helped support the energy-ravenous brains that were evolving at the time. The gathering, sharing, and consumption of meat was, in all likelihood, an important social act as well, one which helped shape interaction in early human groups. Further, those who acquired large amounts of meat may have had enhanced status within the group. It is not, perhaps, too broad of a statement to say that when humans learned how to kill and consume other animals that their rise to dominance in the Animal Kingdom began.
But erectus populations may have done damage to themselves by over-dependence on certain animals. Evidence suggesting this has been found at Qesem Cave, near Tel Aviv, Israel, and GBY. And interestingly enough, this is tied to fat consumption. Primates have a need for fat. The anatomy and physiology of the intestines in great apes, aided by bacteria, allows them to synthesize fat from vegetation, but in humans, the growth of the large intestine, and thus the ability to synthesize fat, was constrained by the growth and energy demands of the brain. Therefore, consuming fat from fat-bearing food sources was the easiest way to acquire this necessity. In the Levant, erectus’s preferred fat source was the elephant Elephas antiquus, a Pleistocene-era variety. About 400,000 ybp there was a disastrous decline in the elephant population in the area. This decline may have been brought about by over-hunting. Evidence from other regions where erectus populations were found shows similar declines in the elephant population. But we cannot say with certainty that over-hunting was the primary cause of this reduction in elephant numbers. In any event, the decline in the number of elephants necessitated the increased hunting of smaller animals, which would have drastically increased the daily energy expenditure (DEE) of the erectus hunters, putting them in a negative spiral of having to kill more animals and having less bodily energy with which to do this.56 But there may have been hominins who were able to take advantage of the situation, ones smaller, more agile, and faster. As the authors of a study of this matter put it,
Our calculations show that the elephant's disappearance from the Levant just before 400 kyr was significant enough an event to have triggered the evolution of a species that was more adept, both physically and mentally, to obtain dense energy (such as fat) from a higher number of smaller, more evasive animals. The concomitant emergence of a new and innovative cultural complex –the Acheulo-Yabrudian, heralds a new set of behavioral habits including changes in hunting and sharing practices that are relevant to our model.57
It is possible, therefore, that a change in the density of certain kinds of animals may have helped trigger the evolution of the humans who would ultimately replace erectus—sapiens. Obviously, much more research is needed on this line of inquiry, which remains an intriguing hypothesis rather than a universally accepted fact. But the possibility that this hypothesis is valid seems indisputable.
Meat eating appears to have had other consequences as well. Carnivores store an enormous amount of vitamin A in their livers. Consuming a carnivore’s liver can cause an agonizingly painful, even lethal condition known as vitamin A poisoning. There is evidence that the erectus specimen KNM-ER 1808, a female, suffered from this ailment. Moreover, since she survived many weeks or even months with this condition (judging by the damage to her bones), it appears that other members of her group must have cared for her, otherwise she would not have lasted more than a couple of days. Someone must have brought her water, for example, implying the existence of some sort of vessel for carrying it. More importantly, the evidence that she was cared for reveals something even more important: that 1,700,000 years ago erectus displayed sociality, a loyalty to the group’s members and a sense that the members of the group were committed to each other’s well-being. This may have been an important factor in the long survival of the species.58
Finally, did erectus possess spoken language of any kind? In its earliest phases, probably not. This conclusion rests on an analysis of the only skull of an erectus infant ever recovered, one known as the Mojokerto child, unearthed at Perning, Indonesia in the 1930s. The child was probably between six months and eighteen months of age when it died. The specimen is an almost complete calvaria. None of the child’s dentition exists, however. The specimen has been dated at 1.8 million ybp, making it one of the oldest hominins ever discovered in Indonesia. Judging from the development of various areas of the calvaria and comparing this development to that of modern humans and chimpanzees, it appears that the Mojokerto child had already attained 70% to 90% of its adult brain size. So although we only have a single skull sample here, it would seem that early Homo erectus underwent only a relatively brief period of brain development after birth, and that it is unlikely that it had the cognitive ability to use a complex spoken language.59 However, in my opinion, although the possession of spoken language in early erectus is unlikely, it is quite possible that by the time erectus-like humans attained brain sizes that overlapped with the lower end of the modern human scale that they may indeed have had the capacity for spoken communication. The question is still an open one.
Homo erectus had a long career on this planet. Its tool-making tradition, its use (in some areas, at least) of fire, its hunting tradition, and its social traditions helped establish the genus Homo in many areas of the eastern hemisphere. In some areas, particularly the Middle East, north Africa, southern Europe (perhaps), and east Africa its skills became part of the survival strategy of those who succeeded it. Erectus did not display a large capacity for technological innovation. The Acheulian toolkit retained many of its characteristic tools for hundreds of thousands of years. Nor were erectus’s numbers very great. A recent estimate made by a geneticist indicates that the entire erectus population 1.2 million ybp may have been only about 55,000.60 In contrast, a specialist in demography has recently “very roughly” estimated the erectus/ergaster population of Eurasia and Africa prior to 300,000 ybp at between 500,000 and 700,000.61 In either case, the numbers are tiny compared to those of modern sapiens. Erectus could easily have faced extinction well before it had given rise to any successor species. On such a tenuous and fragile base did the rise of modern humans rest.
WHAT WAS THE ROLE OF HOMO HEIDELBERGENSIS IN HUMAN EVOLUTION?
The human remains we have unearthed from the mid-Pleistocene Age, the period from around 800,000 to around 200,000 ybp, have been the subject of many conflicting hypotheses over the years. However, what paleoanthropologists once called “the muddle in the middle” is slowly being clarified. Many paleoanthropologists are convinced that there was an intermediate species between erectus and sapiens. These scientists contend—although there is far from a consensus on this point—that this species, and not erectus, was the first variety of human to establish a long lineage in Europe, and that this intermediate species also had an African variant. The designation of this variety of human as a separate species is a controversial one in the eyes of some scientists, but H. heidelbergensis’ combination of erectus-like physical traits and more derived features, with a brain that was apparently fairly sophisticated, has persuaded many researchers that its role in human evolution was a crucial one.62
The first specimen attributed to H. heidelbergensis was discovered in Germany in 1907 and formally described in 1908. It was a lower jaw with dentition and an intact ramus on each side, called the Mauer mandible (named for the locale near which it was discovered). The jaw was an unusual one, fairly robust in its basic structure but possessing relatively small teeth. It has been dated to around 600,000 ybp. Since that initial discovery, a number of significant finds attributed to H. heidelbergensis have been made. Kabwe 1 (or Broken Hill), a cranium with some of the upper jaw dentition, a large face and a very large supraorbital torus, probably from an adult male, with an endocranial volume of about 1280cc, was found in Zambia and is perhaps older than 780,000 years. Bodo, a partial cranium, probably an adult male from the Middle Awash Valley in Ethiopia, with a large face, prominent supraorbital torus, and an endocranial volume of about 1250cc, is dated to 600,000 ybp. Boxgrove 1, a section of a left tibia, about 300mm in length, found at the Boxgrove archaeological site in the UK, is dated to around 500,000 ybp. Arago XXI, a skull, probably male, with a complete face and part of the cranial vault, from the mid-Pleistocene of France is dated at around 400,000 years old (but is possibly older). Apidima 2, is an almost complete skull from the Middle Pleistocene of southern Greece. (Efforts to determine a more specific date have been inconclusive.) The Petralona Cranium, also from Greece, is dated from 150,000 to 200,000 ybp.63 Cranium 5 from the Sima de los Huesos site at Atapuerca, described by Donald Johanson as “the most complete pre-modern skull in the fossil record”, has a cranial capacity of 1125cc. Cranium 4 is from the same site and has a cranial capacity of 1390cc.64 It is dated, along with Cranium 5, at greater than 300,000 years.65 And the Steinheim Skull from Germany, a mostly complete cranium with some of the upper jaw dentition, possibly an adult female, with a cranial capacity between 1100 and 1200cc, is dated to about 250,000 years.66 In the shape of various features on them, Cranium 4, Cranium 5, and the Steinheim Skull clearly exhibit certain Neanderthal-like traits.
What was H. heidelbergensis (if we accept it as a valid taxon)? There are observers who contend that it was a true multi-continent species, with African, European, and possibly Asian representatives. Certainly there are strong similarities between the European and African specimens. The most striking aspect of the species was its high level of encephalization, with an average cranial capacity of just over 1200cc compared to the average erectus size of less than 1000cc [bearing in mind, of course, that late erectus specimens were of much greater brain size than the earliest ones]. H. heidelbergensis appears to have attained a higher level of technological advances than erectus as well.67 But there are researchers who contend that what is being labeled H. heidelbergensis is simply the latter form of erectus, and that its anatomical differences are evidence of variety within erectus, and not the existence of a separate species.
Recent research has tended to bolster the status of heidelbergensis as a valid taxon, but there are still questions about which specimens deserve inclusion in it and the specific timeframe in which it evolved. A particularly intriguing specimen is known as the Ceprano calvarium, from an Italian site dated at between 430,000 and 385,000 ybp. The calvarium displays an unusual mixture of traits, some primitive, some derived. Researchers who have compared it to a wide range of African and Eurasian specimens have concluded that Ceprano, with its combination of features, may be a skull that connects Mid-Pleistocene humans from a number of different regions, in the sense that it incorporates their traits. Ceprano, in this comparative study, appears to have been the product of a dispersal of hominins that began somewhere around 780,000 years ago. It may, in fact, at 400,000 ybp, represent a bridge between erectus and heidelbergensis. The calvarium may also be a counterpart (anatomically) to the Mauer mandible.68 The Ceprano calvarium, therefore, may be a representative of the base of heidelbergensis, (which would then cause us to rethink our view of the Boxgrove, Kabwe, and Bodo specimens), or it may be a late representative of an archaic form of heidelbergensis.
There seems to be a growing consensus that the original heidelbergensis species underwent allopatric speciation (meaning speciation caused primarily by geographic isolation), producing distinct African and European lineages. [Was Ceprano, living in southern Italy, an indication of this branching?] According to this hypothesis, the European lineage produced H. neanderthalensis, a species that lasted, in various places, for more than 200,000 years. In this scenario, the African lineage produced a somewhat more successful variant. It is the African branch of H. heidelbergensis that may have given rise to Homo sapiens. In this view, heidelbergensis itself evolved out of the African form of erectus, erectus sensu lato, rather than the Asian form, erectus sensu stricto. There appear to have been, however, many subpopulations within the larger groupings (one of which, for example, has been labeled H. h. rhodesiensis) and these localized variants may have been evolutionary dead-ends. Further, the status of Homo antecessor needs clarification as well. Was it ancestral to heidelbergensis or a localized variant within it? But the picture in some ways, is becoming clearer: somewhere between 1 million and 500,000 ybp significant changes occurred in the genus Homo, ones that ultimately gave rise to modern humans, although the whole set of human phylogenetic relationships in that era has not yet, by any means, been elucidated.69 But the members of heidelbergensis that lived in east Africa may be the group from which our direct ancestors evolved.
Culturally, H. heidelbergensis seems to have outstripped the erectus populations surviving in parts of Asia. Homo heidelbergensis is associated with the oldest verified hunting weapons, four spears approximately two meters in length and sharpened at both ends, found in Germany and dated at a remarkable 400,000 ybp.70 It most definitely had command of fire, and it and its (probable) Neanderthal descendants flourished in cold regions. Perhaps most significantly, H. heidelbergensis is thought to have made one of the major breakthroughs in the history of our genus: it appears to have been the first human type to build artificial shelters, as the evidence of hut construction at Terra Amata, on the southern coast of France [within the boundaries of Nice], seems to indicate. There appears to have been a hearth among these shelters as well, and the site is dated at 350,000 to 400,000 ybp. Further evidence of shelters and hearths has been found at Bilzingsleben, Germany, also dated at around 350,000 ybp.71 Coupled with the evidence of spear-making in this general era, we can say, perhaps, that the high level of encephalization in H. heidelbergensis was beginning to manifest itself in cultural breakthroughs, breakthroughs that proved to be of tremendous utility for the survival and reproductive success of the species and its successors.
Haltingly and unevenly, pre-modern humans learned how to survive, leaving evidence in territories ranging from Ethiopia to Java, from Zambia to Korea, from Britain to Israel. It took hundreds of thousands of years for them to learn how to hack tools out of stone, use animal bones and branches to do work, use and then create fire, kill other animals and cook them, create weapons, find and then build shelters, and (presumably) clothe themselves from the hides of the animals they hunted. So readily do we speak of the time in which these things developed that we sometimes overlook the fact that when we say, for example, Homo erectus may have survived in China for about 900,000 years, we are talking about a length of time 180 times longer than all the time that has passed since the origin of the first Egyptian dynasty. The pace of change and development in the ancient human world was inconceivably slow by our standards. It took many centuries for cultural developments to be transmitted across the surface of the eastern hemisphere, carried by nomadic populations trying to make a living in diverse environments. We must assume that certain human populations had to learn virtually everything “from scratch”. Skill sets may have been lost or forgotten, and whole cultures may have disappeared because of this. How many human ways of life have been lost, forever to remain hidden from us?
Our knowledge of this world is frustratingly incomplete, resting as it does on remains that often give us only glimpses of the physical nature and life of our forebears. But one fact stands out: intelligence was their key survival skill. It was reproductively useful, and in being so, was selected. As the level of encephalization among humans increased over time, and the density and interconnectedness of the neurons in their progressively larger brains became more complex, so did their comprehension of the world, and with it, an ability to bend the world (if only in small ways) to their purposes. Physical strength and endurance were, of course, of tremendous importance in the often brutally-challenging worlds of 1,000,000 or 500,000 years ago. But the ability to assess the resources, both plant and animal, of an area, plan and organize work, interact with and communicate (in some way, if not necessarily by means of language) with the others in one’s group all rested on the possession of large, highly organized brains. It is doubtful that any human in the era prior to the evolution of modern humans had the faintest inkling of this. But it was the gelatinous tissue in their heads that was the source of all their ability to make their way through life on this tiny, insignificant planet, a world that seemed so huge and dangerous to them. They had come to possess consciousness, perhaps not a unique human trait but one so highly developed in their genus as to set it apart from all others. They probably assumed the world was exactly as their senses told them it was. Only later were humans to realize this was not the case. And did our pre-modern ancestors already imagine an unseen world of ghosts, spirits, gods, and demons? Or were these beliefs the product of brains more able to conceive of them than theirs were?
The Emergence of Homo Sapiens
We are now finally at that stage of the story where humans we would recognize as our kind are beginning to take their place in the world. Their emergence was ultimately to be of immense significance to the biosphere of the little planet, and they would eventually establish a true planet-wide culture. What kind of animals are they? Members of Homo sapiens are differentiated from other species of humans by the following basic anatomical characteristics:
--An average brain size of approximately 1300cc, [other estimates range up to 1350cc] smaller in absolute terms than Neanderthals (about whom we will say much more in the next chapter) but larger in relation to their average body size than any other kind of human.
--A skull with greater height than the skulls of previous species of humans, and one which is shorter in length (back to front) relative to its height than those of other hominins as well.
--The lack of a conspicuous brow ridge, although the very earliest members of sapiens had a more prominent supraorbital torus than we.
--A smaller face than other hominins, and a face that is completely below rather than in front of the front section of the brain. The face also has indentations below each of the eye orbits, known as the canine fossa.
--The presence of a true chin, a smaller jaw than other hominins, and smaller dentition.
--The postcranial skeleton is lighter than that of other species of humans, without the bone thicknesses displayed in many parts of the Neanderthal skeleton.72
What is perhaps the most significant trait of Homo sapiens is its highly developed prefrontal cortex, the part of the brain that deals with various “executive” functions, one that maintains much of the emotional and behavioral stability in a human, and one which is deeply important in many human cognitive functions. The human prefrontal cortex is proportionately much larger than that of the great apes. But it is not simply the size of the human prefrontal cortex that matters, it is the complexity of its internal organization. Homo sapiens may have succeeded because its prefrontal cortex’s organization was superior to anything that had ever come before it. We can infer this (perhaps) because sapiens was the first species we know of to develop symbolic communication in various forms. Further, it may have been the first species to create physical representations of objects found in the environment. (But see p. 378.) The evidence is sketchy, obviously, in regard to the earlier species of humans, but so far most symbols and art objects in existence seem to be the product of sapiens’ mentality. It must also be noted that sapiens seems to have existed for many tens of thousands of years prior to producing such things.
The earliest Homo sapiens remains were found where so many other hominid remains have been unearthed, in the Omo region of Ethiopia. The remains consist of two partial crania, with some postcranial material as well. In 2008 an earlier announcement (2005) was confirmed: after a careful re-dating of remains that had been found several decades earlier, the oldest specimens of our species are approximately 195,000 years old.73 (When we consider Australopithecus afarensis, there may have been a continuous hominid occupation of Ethiopia longer than any other region on Earth.) Molecular evidence appears to indicate a divergence from the African heidelbergensis (?) population about 200,000 years ago, and this date appears to be the most likely one for the emergence of modern humans.
At about the same time sapiens was emerging, the last remnants of Homo erectus in China were dying out. There were small populations of erectus in Indonesia. In Europe, the Neanderthals were established. The climate of the Earth was mild.
Then the world began to change.
Around 195,000 years ago, the planet’s benign climate began to grow considerably colder and drier. In the northern latitudes, a period of glaciation known as Marine Isotope Stage 6 (MIS6) set in. In Africa, deserts spread and the food supply dwindled. Genetic studies indicate that the Homo sapiens breeding population (those in the potential reproductive stage of life) collapsed, from an estimated 10,000 individuals down to just a few hundred. In desperation, one of the sapiens populations migrated southward, eventually reaching the southern tip of Africa, a place we now call Pinnacle Point. There members of the group stayed, generation after generation, from about 164,000 to 35,000 years ago. (Some sapiens appear to have stayed behind in east Africa.) They developed the most advanced culture that had ever existed, learning how to harvest the abundant marine life the nearby ocean offered and eating the various tubers and bulbs (collectively known as geophytes) that grew in the region. They used fire to heat-treat stone, thereby making the fashioning of their excellent stone tools easier. Most strikingly, perhaps, there is evidence that they adorned themselves with seashells and used red ocher to draw symbols on the walls of Blombos Cave. Moreover, they taught all these skills effectively for tens of thousands of years. The conclusion is a compelling one: the Homo sapiens of Pinnacle Point were cognitively modern. They saw the world with an intelligence like ours. Not all of the community’s members stayed. As the weather became more moderate, (beginning about 123,000 years ago) apparently groups of them began moving northward again. (Some groups may have begun their migration prior to this, as there is some evidence of out-of-Africa migration as early as 125,000 ybp.) Eventually, descendants of the original refugees would radiate out of Africa and travel across first the entire eastern hemisphere, and then the entire length of the western hemisphere. The genetic evidence we have gathered leads us to an inescapable conclusion: The majority of human beings alive on this planet today may be descendants of the Homo sapiens who lived at Pinnacle Point.74 It is to the story of how Homo sapiens spread across the world’s landmasses that we will now turn.