Debunking Man the Hunter

y are we the way we are? What makes us think and act the way re do? Birds fly and snakes slither because they must. What are we impelled to do? Well, humans walk upright, they verbalize language, and they manipulate their environment to suit their needs. But did we start out with those legacies or did they come slowly over time? Yes, most birds fly, but the ancestors of birds were probably terrestrial dinosaurs. Snakes slither, but the skeletal remnants of hind legs are found in primitive snakes. Considering these strange and drastic developments over time in other animals, we might well question in what state of nature we humans may have started out. To look generally at our past and specifically at our position in the food chain—predator or prey?—we need to study our roots; we need to get down to the very beginnings of the first steps on the human path.

The evolution of our species—Homo sapiens—is a story told in fits and starts, through new fossil discoveries and breaking headline news. Missing Link Found is often the lead in any media report about new findings in our hominid line. The "missing link" has not yet been found and is—in scientific terms—a quite inappropriate term. Missing Common Ancestor of Chimps and Humans Found would be the correct (but not nearly as generally exciting) headline that would stun the world of paleontology. That would be the find! The one sought by every researcher who spends years raising research money through grant-writing and then years more painstakingly grubbing in out-of-the-way locations for fossils—the elusive creature at mile-marker zero of our evolutionary highway whose progeny took two different forks in the road. One road led to modern chimpanzees and one led to modern humans. In no way did "we" (modern humans) pass through a stage in which we were chimpanzees. The chimps are as modern in their approach to life in the trees of tropical Africa as we are in our two-legged wandering all over the earth.

The question that drives paleo-detectives to distraction is when did that fork in the road appear?

First, a cautionary disclaimer. As has been the case with every volume published that contains theories of where, when, and what constituted our beginnings, this chapter may be overridden by a new discovery of a fossil hominid that changes the whole story line once again. One irrefutable statement, though, is that our hominid lineage begins much farther back in geologic time than science estimated a decade ago. Even in the 1990s, 4-million-year-old petrified remains were considered close to the seminal divergence from a common ancestor with chimps. Now, six-to-seven-million-year-old fossils have been discovered in the African nations of Chad and Kenya. Newly discovered finds appear to be ho-minid species that lived sometime after the chimpanzee and the human lines diverged from a common ancestor because they show evidence of upright walking, or bipedalism—which is a trait of humans but not of chimpanzees.

It is only fair to state that the oldest known hominid fossils have their detractors. The major controversy revolves around whether the fossil remains do indeed indicate bipedality, which is the initial and singular characteristic most indicative of hominid lineage. Pelvis, knee, and leg bones will answer this question quite nicely, but what if those are not among the retrieved remnants of long-deceased kin? Well, if cranial (skull) bones are found, one of the indicators of bipedality is the placement of the foramen magnum, the large hole at the base of the skull through which the spinal cord attaches to the brain. Picture how the back and head of a quadrupedal animal—like a horse for example—is oriented; the spine is on a horizontal plane so the foramen magnum, the entryway to the brain, is positioned high up on the back of the skull. Now visualize a bipedal animal whose spine is on a vertical plane; the foramen magnum is located as far down on the base of the skull as possible. Currently, it is the sense of the anthropology community that the fossils we will discuss here imply obligate bipedal hominids; in other words, they had upright bodies and hips that made bipedal striding the most comfortable form of locomotion and this necessitated the placement of the foramen magnum at the bottom of the skull.

Will the First Hominid Please Stand Up?

Asking for the identity of the first hominid should be an easy entreaty, right? We just mentioned that upright walking was the litmus test of human ancestors. But, even the technical categorization of a hominid has now become more enigmatic than a few years past. Taxonomists—the scientists who immerse themselves in Latin nomenclature to classify species and devise the relationships of all living creatures one to another—have added another layer of stupefaction. First, all monkeys, apes, and humans are primates—that's a given. The latest taxonomic blueprints, however, group orangutans, gorillas, chimpanzees (that is, all the so-called great apes), and humans in the same taxonomic family—designated by the Latin term Hominidae (commonly anglicized to "hominid"). Gorillas, chimps, and humans are subsequently grouped together within the same subfamily level. Why? Because, currently, based on DNA similarities, it is only at the descending level of our genus—Homo—that taxonomists can separate our genetic building blocks from our ape relatives.

Despite total acceptance of this powerful DNA evidence, we realize that the new blueprint, combining humans and apes into one taxonomic family, exponentially increases the bewildering jungle of taxonomy. So, for the sake of ease in reference to our subject matter and to avoid potential esoterica as much as possible, we will continue throughout this book to employ a more conventional approach and distinguish as hominids only those species that diverged from the human-ape stem some 7—10 million years ago and were bipedal. The alternative is repeatedly to identify forerunners to modern humans by their individual Latin names (Australopithecus, Paranthropus, Kenyanthropus, Ardipithecus, Orrorin, and

Sahelanthropus), a decision that would cause this book to be much longer than intended.

Some of those Latin monikers may sound familiar and some are so new they are just entering the most recent editions of college textbooks on hominid evolution. We'll start with Sahelanthropus tchadensis (not a name that exactly ripples off the tongue, but a celebrity nonetheless) because it is the oldest fossil hominid so far discovered. What makes it a paleontologist's dream—and nightmare simultaneously—is that its existence stretches our human history back to between 6 and 7 million years, while at the same time refuting a slew of theories concerning the location and habitat of hominid origins.

Nicknamed Toumai, or "hope of life" in the local Goran language of the Djurab Desert, the fossil was unearthed in the African nation of Chad. Sahelanthropus is represented by a cranium, a jaw fragment, and several teeth. It was found in 2001 by a team of French and Tchadian pa-leoanthropolgists led by Michel Brunet of the University of Poitiers and his colleague Djimdoumalbaye Ahounta. The landlocked equatorial nation of Chad is bounded on the north by Libya, on the south by the Central African Republic, on the east by Sudan, and on the west by Niger, Nigeria, and Cameroon. As is apparent from the geographic description, Chad's location is smack in the center of Africa. The discovery of Toumai was a bit like finding medieval Christian artifacts in the middle of Australia. Fascinating, but how can you reconcile it with traditional theories? And traditional theory had it that Central Africa is a peculiar place to find hominid fossils because it is the "wrong" side of the Rift Valley.

The Great Rift Valley, which stretches from Mozambique in the south up through Ethiopia in the north, is a monstrous gash in the East African landscape. If you are peacefully driving north from Nairobi, Kenya, to Lake Nakuru National Park, at one point you will see an innocuous 12-by-12-inch sign that reads, "Beware the Escarpment." Before you have time to think what that decorous command may imply, you are hurtling over the edge of the Great Rift Valley on a switchback road that seems to angle downward at 45 degrees. Below you lies the valley, stretching endlessly and shimmering in the dry heat. Until the excavations in Chad, all of the earliest hominid fossils have been found on the east side of the Rift Valley (Ethiopia, Kenya, and Tanzania to be specific). One neat, and now retired, theory stated that when chimps and hominids evolved from their common ancestor, the chimp line stayed in the trees of the forested region to the west of the Rift Valley and the hominids began—successfully and bipedally—to colonize the drier savannas of the east. This ceased to be a viable theory when hominid fossils started popping up in places on the west side of the Rift, like Chad.

The Great Rift Valley of East Africa is shaded. To date, only two early hominid fossils have been found west of the Rift Valley. (C. Rudloff)

As often happens behind closed doors, when the startling fossil description of Toumai was published in Nature in July 2002, pundits tended to remark something on the order of "It'd be better if they had covered it back up!"—echoing the frustration of fitting this new piece into the paleo puzzle. And who is to say that fossils are not to be found in other unexamined areas of interest to anthropologists. For instance, Malawi in southeastern Africa, said to lie in a "hominid corridor" between the fossil-rich eastern and southern regions of the continent, has been tossed out as a fresh, new location to investigate for ancient hominid bones.

The second oldest of the hominid finds (represented by the thigh bone, teeth, and lower jaw of an individual estimated to have lived 6 million years ago) startled the world of anthropology likewise. French researchers Brigette Senut and Martin Pickford discovered Orrorin tuge-nensis (called "Millennium Man" because of the relic's unveiling at the dawn of the new age) in the Tugen Hills, Baringo region of Kenya. Senut and Pickford had only a short interval to revel in finding the 6-million-year-old fossil and publishing their findings before the more ancient Toumai from Chad was stealing the show.

As we work our way forward over the millions of years from the beginning of smallish bipedal beings to the present, another character in the geologic drama walked on stage. We next encounter Ardithpithecus ramidus ("ardi" meaning ground and "ramid" translating as root in the local Afar language), unearthed in Ethiopia in 1993 by Tim White and Alemayehu Asfaw. This was the first of the excavated hominid remains in excess of 4 million years of age. Bones and teeth of 17 individuals, while highly fragmentary, have been dated at 4.4—5.8 million years ago and a new find of the same species, measured at 5.2—5.8 million years, confirms the great age of this hominid.

Having briefly glanced at these three hominids who we know lived approximately 6 million years or more prior to the present, let's continue meandering through the various life-forms that preceded our own species. Meave Leakey of the famous Leakey clan of paleoanthropologists par excellence—we'll talk about her husband's, father-in-law's, and mother-in-law's stunning discoveries a little later—found Kenyanthropus platyops (this translates as "flat-faced Kenyan man") in the area of Lake Turkana where the Great Rift Valley exits northern Kenya. The emphati cally vertical plane of this fossil face motivated Leakey to suggest K. platy-ops as a direct ancestor to modern humans. (Jutting jaws are considered a trademark of those hominids less likely to be in the direct human ancestry; flat faces are more "human-like.") K. platyops represents a 3.5-million-year-old skull from what Leakey claims may be an entirely new branch of the early human tree.1

All the extinct hominid species we have described so far preceded the legendary "Lucy" (a.k.a. Australopithecus afarensis) found in Ethiopia by Donald Johanson in 1974. Lucy is a hominid fossil with personality. Her discovery was celebrated in the field with a rollicking party that boomed pop music through the desert night. She was named after the Beatles' song "Lucy in the Sky with Diamonds," and Johanson and his colleagues truly rock 'n' rolled the world of science when they presented the nearly complete post-cranial (below the skull) skeleton of a young female hominid who lived 3.2 million years ago. Lucy is thought to have stood upright at 3 and one-half feet (males of her species may have been as much as a foot taller). She was bipedal but had long feet with an exceptionally powerful big toe that was divergent like our modern human thumbs and could be used to grasp and climb trees. She may have exploited the forest fringes, using those grasping toes to evade predators by shinnying up a tree.

Two relatives of Lucy left their footprints in newly fallen ash at another spot in East Africa called Laetoli (these immortalized footfalls constitute another Leakey family find—Mary, the family matriarch, this time). A pair of australopithecines, possibly male and female from the difference in how their respective weights imprinted the ash, were walking side by side over 3 million years ago. Their footprints give a tantalizingly personal nature to australopithecines as individuals. Where were these two going? Were they a mated pair? What might they have been leaving or going toward on their journey?

A "robust" relative of Lucy (Paranthropus boisei) had been discovered at Olduvai Gorge in Tanzania by the incomparable first-generation husband-and-wife team of fossil-hunting Leakeys—Louis and Mary—in the 1960s. The "robust" appellation doesn't refer to any gigantic stature of the prehistoric hominid but to the incredibly large jaws and huge molars possessed by this particular branch of the family tree, making them capable of grinding hard, fibrous plant material. Another robust species of early hominid was

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