Masters of the Planet (15 page)

Cranium of Olduvai Hominid 5, a.k.a. “Zinjanthropus,” a robust australopith of the species
Paranthropus boisei,
from Olduvai Gorge, Tanzania. 1.8 million years old. Drawing by Don McGranaghan.

Still, they did not have to wait long to find what in their terms was a much better candidate for the honor of being the long-sought Olduvai Toolmaker. For in 1961, at about the same geological level in the Gorge as the
Paranthropus,
Louis reported a lower jaw of a much more gracile hominid. Various people at the time noted striking similarities between the teeth of this specimen and those of
Australopithecus africanus;
but Leakey was undeterred in his search for early
Homo,
and a few years later he and some colleagues made the Olduvai jaw the holotype of
Homo habilis,
“handy man,” named of course for its presumed manual skills. Thus began the paleoanthropological tradition of routinely assigning East African early gracile hominids not to the genus
Australopithecus,
but to our own genus
Homo—
a tradition that was only broken a decade and a half later, when the much earlier and more robust
Australopithecus afarensis
was first announced from Hadar and Laetoli. Those fifteen intervening years were very eventful ones in paleoanthropology.

In deference to tradition, we will return to the gracile Olduvai hominid and other such fossils in
chapter 5,
when we look at the evidence for the origin of the genus
Homo.
Meanwhile, though, the robust australopith from Olduvai became simply the first of many such fossils to be published from sites in Tanzania, Kenya, and Ethiopia. In the 1960s, expeditions to contiguous regions of southern Ethiopia and northern Kenya turned up evidence of fossil hominids in the time frame between about 2.6 and 1.5 million years ago. Many of these were “hyper-robusts.” The earliest of them, in the 2.6- to 2.0-million-year bracket, came from the Omo Basin in southern Ethiopia, and were pretty fragmentary. Still, the jaw fragments were massive; and because they contained the same combination of huge, flat molars and tiny front teeth seen in Nutcracker Man, they were generally assigned to
Paranthropus boisei—
though one toothless jaw some 2.6 million years old received the name
Paranthropus aethiopicus,
for the country in which it was found.

Just to the south, on the eastern shores of Lake Turkana in northern Kenya, somewhat younger (1.9- to 1.5-million-year-old) robust
australopiths
began to show up in the late 1960s. These included one pretty complete, albeit toothless, robust skull that looks rather different from the Olduvai robust specimen, with a much broader and shorter face. Still, its dental proportions would have been basically similar and it, too, was assigned to the species
Paranthropus boisei.
Interestingly, we now know a frontal bone from East Turkana that looks just like its counterpart in the Olduvai cranium, and different from its Kenyan coeval. So the betting might be that we have more than one kind of robust australopith represented in the Turkana Basin at around 1.9 million years ago. Whatever the case, all of the East African hyper-robusts had similarly huge molar teeth that recent isotopic analyses have suggested were used to process large quantities of low-quality plant foods such as grasses and sedges. Apparently their diet was much more specialized than that of their South African relatives, and they may have been an exception to the rule of australopith omnivory.

One of the most exciting robust australopith finds at East Turkana was made in 1970, with the discovery of a partial skull of an individual who had been much smaller than the owner of the toothless robust skull, but who had belonged to the same species. Here at last was good evidence of sexual dimorphism—marked size differences between males and females—in robust australopiths. This find put an end, once and for
all,
to any lingering desire to categorize the robusts and graciles as males and females of the same kind of hominid, for it showed that female robusts didn't look like graciles, but rather like smaller versions of the robust males.

The “Black Skull,” KNM-WT 17000, from Lomekwi, Kenya. Some 2.5 million years old, this is the most complete skull we have of the species
Paranthropus aethiopicus,
the earliest species of the “robust” australopith lineage.

Work continued in East Turkana through the 1970s, but in the 1980s the focus of attention in the Turkana Basin moved to the western side of the lake, where slightly older fossil-bearing deposits were coming to light. In 1985 a famous specimen dubbed “the Black Skull” turned up. This specimen has many of the cranial characteristics of
Paranthropus boisei,
but its face is longer and concave in profile, and the braincase shows marked sagittal cresting at the very rear. The consensus rapidly developed that here was a form, ancestral both to
P. boisei
and to the South African robusts, which took the robust lineage back in time to 2.5 million years ago. Largely as a matter of convenience, it has been given the name of
Paranthropus aethiopicus
(after that jaw from Omo). At the other end of the time range, a 1.4-million-year-old skull from a place called Konso in southern Ethiopia has been identified as the last-known survivor of
Paranthropus boisei
—indeed, the last-known australopith of any kind. By that time, members of our genus
Homo
were all over the landscape; and indeed, advanced stone tools of the kind otherwise associated only with
Homo
fossils are also known from the Konso deposits.

Despite their strikingly different histories of interpretation, the eastern and southern African records are thus both beginning to give us a picture of the australopiths as a vigorous adaptive radiation, in which a whole variety of different early biped species were actively experimenting with ways to exploit their hominid heritage. Yet as far as we can tell, the basic pattern of adaptation—bodies light enough for agility in the trees, so fairly small, with a broad pelvis and short legs; omnivorous habits and with mobile forelimbs; relatively small-brained yet manually adept—persisted, even after the invention of stone tools announced that these revolutionary yet physically archaic (compared to us) creatures had developed an entirely new way of perceiving and dealing with the world. Theirs was truly a successful physical and behavioral strategy; and although it bridged the gap between the ancestral existence in the forest and the future occupation of open territory, it cannot be described as in any way “transitional” between the two. It
was
a way of life entirely unto itself, and it lingered on well after the point at which recognizable members of our genus
Homo
had come on the scene. Still, eventually the australopiths succumbed to those closer human relatives. Evidently, early
Homo
were invincible competitors, even if they were in competition for only a portion of the resources that the australopiths had exploited.

But even then the picture is not yet complete. In 2001, paleoanthropologists from the Kenya National Museums in Nairobi announced the discovery of a tantalizingly different fossil hominid, from sites to the west of Lake Turkana dating from 3.5 to 3.2 million years ago. The principal specimen is a crushed and cracked cranium that, even allowing for some distortion, is different from any of the other hominids known from the Turkana Basin. The chewing teeth seem to have been thick-enameled but quite small; and the skull itself is notably short-faced, hence the name
Kenyanthropus platyops
(“flat-faced Kenyan man”) that the finders chose for their new fossil. Sadly, the condition of the specimen does not allow us to say much more about it; but the describers noticed distinct similarities to a skull known from much later deposits at East Turkana. Identified by the unromantic moniker of KNM-ER 1470 (its museum catalog number) this 1.9-million-year-old fossil (with a brain size a bit above the australopith range) had gained some notoriety in the early 1970s as the first skull to be discovered of
Homo habilis
—thus appearing to prove the reality of this species, since it didn't look like any known australopith. The unfortunate truth, however, is that this specimen also is so poorly preserved that it is difficult to know what to do with it. We'll look more closely at this fossil in the next chapter; suffice it to say here that placing it in
Kenyanthropus
seems for the time being to make eminent sense, if only because it sits very uncomfortably with either
Australopithecus
or
Homo.

Clearly, a lot more was going on in human evolution at the end of the Pliocene than just the gradual refinement of a single central hominid lineage. The number of australopith species that we recognize from this late stage is multiplying, especially with the finding of forms such as
Australopithecus sediba
which appears to have a number of advanced features, especially in the pelvis, that does not at all have the dramatic sideways flare that we saw in Lucy's. This is also the time when the first claimed members of the genus
Homo
begin to appear, and whether or not they deserve this title it is becoming abundantly clear that this was a time of great evolutionary ferment among our precursors. The hominid stage was packed with actors, all pushing and shoving for the limelight; and the only thing we can be sure of is that the australopiths ultimately lost out.

FIVE

STRIDING OUT

People have referred to themselves as “human” since long before anyone had the faintest idea that our species is connected to the rest of the natural world by an extended series of long-vanished intermediate forms. And, at least until the notion came along that all living things are connected by ancestry, there was no compelling reason to define the term “human” precisely. This is why, a century before Charles Darwin published
On the Origin of Species,
the great Swedish natural historian Carolus Linnaeus was content to brush off
Homo sapiens
with the remark
nosce te ipsum
(know thyself). (Linnaeus gave us the system of classifying organisms that we use today, and one of his great innovations was to furnish diagnostic physical characters for every other species he named.) Clearly, Linnaeus and his contemporaries felt that our species is so distinct from all other living creatures as not to require formal delineation. And who could blame them for that? Given what was known of our zoological context in the eighteenth century, defining exactly what humans are simply wasn't a practical scientific problem, even though it had long entertained philosophers.

Today, though, it's different. For while we are the only “human” beings currently alive on Earth, we now know we have a whole range of close relatives—much closer than the apes—that are now extinct. What's more, those fossil relatives become more and more unlike ourselves as we trace them back in time. This naturally raises the matter of when
exactly
our precursors became “human,” a query that obviously leads one also to ask just what changes that transition may have involved. But while these questions are obvious ones to pose, and have been asked regularly for well over a century, this doesn't mean they have been answered to everyone's or even to anyone's satisfaction. “Human” means different things to different people, and even to the same person in different situations. For example, I am happy to use the term “human evolution” when referring to the entire history of humankind, back to its common ancestor with today's great apes. In that context, the term “human” is pretty much equivalent to “hominid.” But does this really imply that all hominids are “human”? I, for one, would be very reluctant to use this term to describe any of the bipedal ape species that populate the first few million years of that history; and indeed I only find anything I might want to call “fully human” at the very uppermost tip of the human evolutionary tree. But that's just an opinion, and there's plenty of room for legitimate disagreement here—there is certainly no official, or even generally accepted, definition of this elusive word “human.” Remarkably, we have hardly advanced in this respect since, some two and a half centuries ago, Linnaeus's almost exact contemporary Samuel Johnson defined
human
in his great English Dictionary as “having the qualities of a man,” and
man
as “a human being.” Still, even though paleoanthropologists are a famously argumentative breed, it's probably fair to say that most of us broadly concur that the first creatures we can in some meaningful sense call “humans” are the most ancient representatives in the fossil record of our own genus
Homo.