The Sediments of Time

by Meave Leakey

  The little trouble transpired to be a run-in with an extremely hostile rent-a-mob, where he was beaten over the head with batons and severely lashed with a hippo-hide whip at least thirty times across his back. Among the other Safina members present, two were hurt so badly that they were in intensive care. Because the foreign correspondent Louise Tunbridge was also badly beaten at the rally, we heard a terrifying graphic description of the incident on the BBC World Service that evening. Richard later admitted the severity of the situation to me and revealed that his greatest fear had been losing his footing on his prosthetic legs, because if he had been jostled to the ground, he would assuredly have been trampled to death. With the main roads blocked off by police, they escaped through the safety of the slums, where Safina enjoyed widespread support, in the shell of Richard’s vehicle, its windscreen and windows completely smashed.

  * * *

  NZUBE’S FOSSIL came out beautifully that magical afternoon in 1994 at Kanapoi—a complete lower jaw that we immediately suspected was not the same as A. afarensis. We hastened back to camp to compare it with the Hadar casts and Nzube’s beautiful set of lower teeth. Talk about closing the season the following week quickly turned to talk about how long it would take to sieve this new specimen. Starting at the bottom at the edge of the sandy streambed, we steadily sieved the slope. We were very excited, especially after we recovered an isolated molar tooth at the bottom of the slope. But over the succeeding days, our hopes faded as we proceeded closer and closer to the top of the slope, and it became clear that nothing further was going to emerge. We would have to wait until the following year to excavate this bed and see if there could be something more emerging from the layer where it was originally buried. We swept the site clean, placed two rows of protective stones to prevent erosion, and finished up on the last day in the late morning.

  Despite the frustrating days sieving, I could barely believe my luck. In just one season, I had enough fossils to answer some of our most pressing questions. Plus, the cache of exciting hominin finds was exactly what I needed to assure the National Geographic Society that they should continue to support the research. I simply could not wait to get back to Nairobi to compare them all in detail and enlist the expertise of my colleagues. How different will our hominin be from A. afarensis, and where will it belong on the family tree?

  The crew began dismantling the camp, eager to see their families again after a long field season. In no time at all, most of the tents were down, and we continued loading by moonlight until our home for the past three months was securely stowed and tied down in the lorry, and the stash of fossils carefully wrapped and arranged in cartons and padded trays in the back of the other vehicles. We slept on mattresses laid out on tarpaulins, rising early to begin the long trip back to Nairobi. Little did we know that one further adventure awaited us before we would get home.

  In the morning, try as we might, we could not persuade my normally reliable Land Rover to start. We tried all the usual tricks—we cleaned out the fuel filter and the fuel lines; we looked at the fuel pump and the spare-tank switch. The Land Rover was a Defender model with a diesel engine. These workhorses can almost always be started by towing, but by midmorning, we had towed it all over the place to no avail.

  “We’re just going to have to tow it to Lokichar to find a mechanic who can help,” Kamoya decided. Lokichar is the town at the junction with the tarmac trunk road to Nairobi and is a great distance away. We set off gingerly, using an old and worn tow rope that looked rather feeble. We did not get past the first small gulley before it snapped. The same thing happened again and again, and the tow rope was getting shorter and shorter. The first Kalabata crossing was difficult, but we managed to navigate the soft sand without having to do more than push in several places. The second crossing was more challenging and required plenty of pushing as well as lining the ruts in the road with palm leaves to provide traction against the soft sand. We got to the third crossing at noon and did not make it to the other side until two o’clock. We were exhausted and hot after unloading all of our carefully packed equipment from the car. We had hoped to have been well on our way to Kitale by now, a town halfway home.

  “We won’t even make it to Loperot at this rate!” I exclaimed in despair as the tattered tow rope broke yet again. “We have to, so we will” was the unflappable Kamoya’s reply. Loperot, halfway between our camp and Lokichar, was unlikely to have a mechanic, assuming we got that far. We sent Benson—an excellent fossil hunter and jack-of-all-trades—ahead to Lokichar in the lorry so he could call our friend Bob Campbell. Bob’s immense knowledge of engines and bush mechanics seemed like our best hope of starting the obstinate engine.

  Bob racked his brain to think of something that would help Benson trace the fault, the faint line crackling and the coins dropping away as the minutes ticked by. “We already tried that!” Benson replied in frustration to everything Bob suggested. The best Bob could think of was to make sure there was no air in the fuel lines and that fuel was definitely reaching the injector pump. Benson’s disappointment was palpable through the crackling interference as he broke the connection. Moments later, a thought flashed through Bob’s head. Could the Land Rover be the victim of an electrical fault? He suddenly remembered that when the spark plugs are not igniting the petrol mixture, diesel engines are shut down by cutting off the fuel supply either by mechanical means or an electrical cut-off switch. Bob tried calling the operator to locate the call box, but when he finally got through, nobody was there to answer.

  Benson was already on his way back to our convoy. He had found somebody with two steel rods we could use to jury-rig a tow bar, and he had found a mechanic. The mechanic proved to be singularly unhelpful. He had made only a few cursory checks before a Toyota heading back towards town approached. The mechanic looked at his watch, hailed the vehicle, and jumped in, announcing that he had to be back in Lokichar right way. The tow bar improved matters considerably, however, and by five p.m., we were back at the pay phone in Lokichar.

  “Hello! Bob?” Tired and discouraged, I was calling in desperation to ask if he could suggest anything that we could try next. We’d spent the entire day towing our lifeless Land Rover a mere thirty miles—over sandy roads where even fully functional four-wheel drives tended to bog down. With night fast approaching, the thought of towing the vehicle to the nearest garage at Lodwar was not a happy one. Lodwar lay fifty miles north in the opposite direction of home. The nearest town on the way south was Kapenguria, 110 miles away—but that route takes you from the floor of the Rift Valley up the western wall of the rift through the Marich Pass, a long winding climb of four thousand feet that would surely tax the energy of the towing vehicle.

  Bob immediately broke in before I even had a chance to speak. “I’ve thought of something else that might work. Have a look at the injector pump and see if there is a wire connected to it. If there is, then disconnect it and search for a length of wire to reach from the positive battery terminal down to the connection on the pump.” At least we had something new to try. We followed Bob’s instructions cautiously —but to our immeasurable relief, the engine suddenly sprang to life. It transpired that the starter switch controlling the lifeline to the injector pump was the culprit, a very unusual fault. Tired but happy again, we could head for home first thing in the morning.

  I spent our last night much as I had the first—lying impatiently on the ground beside the vehicle beneath a full moon. I was too worn out to notice that this time it was the rumbling of heavily laden trucks belting by on the main road rather than the flowing Kalabata River that lulled my dreams.

  9

  Another Piece of the Puzzle

  We returned to Nairobi flushed with success and without further mishap. We were harbouring a strong suspicion that we might have hominins that were not only older than Lucy and her kin but that were also something completely new, and I couldn’t wait to study them further. The very first evening upon my return, friend and science writer Virgi
nia Morell telephoned me. “Have you heard the rumour that Tim White has found seventeen hominin skeletons in Ethiopia?” she asked excitedly. “Apparently, it’s something even older than Lucy!” she continued. I had mixed feelings as I fumbled for a reply. If Tim really had found seventeen skeletons, what a boon for our science. But it would make my precious haul seem rather paltry, and I wished we hadn’t made our discoveries at exactly the same time. It was very discomfiting to think that my potentially new species might have already been discovered—and named—elsewhere, and I was most anxious to learn if we had found the same thing.

  It eventually transpired that Tim had not found seventeen skeletons. Shortly after Virginia’s call, he published descriptions of seventeen specimens, mostly teeth and pieces of skull and mandible. He named a new species, Ardipithecus ramidus. Ramid means “root” in the language of the local Afar people, and Tim believed that his 4.4-million-year-old fossils were ancestral to Lucy and the root of the human evolutionary tree. I immediately contacted Tim to congratulate him, and sharing my own news, I suggested that we meet to compare our latest finds. Tim agreed that this would be a good idea, and I arranged to visit Addis Ababa after his return from the field the following January. In the meantime, we set about cleaning our fossils and making plaster of paris replicas in preparation for my visit to Addis.

  Tim was a most gracious host, and throughout my visit, he showed me around the Ethiopian collections, and whenever time allowed, he enthusiastically joined me in making comparisons between our bones. “Look at how human that upper canine looks,” I exclaimed. “Yes, and see how it occludes against the lower premolar,” agreed Tim, as we pored over one of the first specimens he had discovered, which included a very primitive apelike milk molar from a baby as well as some adult teeth including canines and part of the back of a skull. In most higher primates other than humans, the long sharp canine is rather like a dagger, continuously self-sharpening against the lower premolar in a configuration known as the C/P3 complex. Tim was pointing out that Ardipithecus did not share this trait and was rather more human-­looking.

  “And see how the foramen magnum is in a really forward position,” he continued, pointing to the opening at the base of the skull through which the spinal cord leaves the braincase. The position of this hole is an indicator of whether the individual walked on two legs or four because the angle that the head is held varies in different postures. These two features are what had led Tim to cautiously conclude that Ardipithecus ramidus belonged on the human rather than the ape ancestral line. “Well, you need to find some more specimens to tell us if it truly was bipedal or not!” I cheekily suggested, with little inkling of what he was going to show me next.

  Tim then revealed his next and most spectacular surprise of all. He had just returned from an exceptional field season, bearing many parts of a very fragile skeleton that could answer this very question about bipedality. However, the protective plaster casing obscured all but the top of the matrix-encased bones, which were too delicate to handle without preparation. “The bone is so brittle that a mere drop of Bedacryl, carelessly applied, can cause the bone to crumble,” he explained. “I’ve had to use the fine point of a small syringe needle to squeeze tiny amounts of the Bedacryl onto it time and again until it is hard.” I could only peer at the top of the fragile bones peeping through the plaster. It was immensely frustrating, but I was curious and eager.

  Some fifteen years later, Tim published his findings on this skeleton—which included much of the skull and the incredibly rare hands, feet, limbs, and portions of the pelvis. Much could be learned from Ardipi­thecus and it held a few surprises. The most telling of these was how distinct it was from chimpanzees, thus upturning a long-held assumption that chimpanzees represent the primitive condition from which we evolved. In fact, both modern African apes and humans have embarked on separate evolutionary trajectories from our last common ancestor.

  Ardipithecus was able to climb along tree branches on all fours but also walked upright on two legs. It had long relatively dexterous fingers with flexible joints that allowed the body to be supported on the palms while moving through the trees. It lacked the morphology that allows the “knuckle walking” characteristic of chimps and gorillas. Its feet, however, retained the opposable, grasping big toe that would be useful for climbing, which has disappeared in fully bipedal hominins.

  From my time in Addis with Tim, it quickly became obvious that our Kanapoi hominin was not the same as Ardipithecus ramidus. The latter was a small, primitive, apelike species with very thinly enameled teeth and relatively large canines. These contrasted with the thickly enameled and relatively smaller canines of the Kanapoi specimens. But were our bones from Kanapoi the same as Australopithecus afarensis? This was the question that I now most wanted to answer, and I discussed it at length with Tim.

  But further study to decide if our fossils represented afarensis or a new species would have to wait. I was leaving almost immediately for a short field season on the east side of the lake with Alan Walker and the crew. While I chafed at the delay, I was somewhat consoled that at least we would be looking for fossils of a similar age to Kanapoi. If I was lucky, we might turn up still more answers.

  * * *

  IN 1987, several hominin teeth had been discovered by John Kimengich at Allia Bay, which lies to the south of Koobi Fora and marks the southern boundary of Sibiloi National Park. They were washing out of an ancient bone bed that was chockablock with fossils, so there was a good chance that more hominins might be found. In 1988, we had put in a small excavation and had indeed recovered more hominin teeth and a piece of mandible. Moreover, the Allia Bay exposures had been dated at 3.9 million years, right between the older Kanapoi and Ardipithecus fossils and the afarensis material. Thus, the site was of huge significance; these were the oldest hominins that we had from the east side of the lake, and they were only slightly younger than the ones from Kanapoi. By 1995, the site was in danger from erosion and it urgently needed excavating before it washed away completely. I had been worrying about how to find the time and the funds for this until Alan Walker provided a solution when he raised funds from the American National Science Foundation for this task. For the next three years, we spent January and February at Allia Bay and June to August at Kanapoi. This hectic field program left little time for catching up with the inevitable backlog of office work and admin, let alone time for studying the fossils.

  The fossils in the Allia Bay bone bed were entombed in a cement-hard matrix and had to be extracted at a painstakingly slow pace. Although much of the bone was rolled and fragmented, we recovered some well-preserved hominin specimens, including several isolated teeth and a maxilla. In the three years we spent working this site, we excavated 115 square metres and recovered eighteen hominins—that’s a surprisingly high density of one hominin for every 6.4 square metres. These were jumbled up with a plethora of other bones belonging to crocodiles, bovids, pigs, and a host of other animals. This rich assemblage of animal bones again confirmed that by four million years ago the transition that we’d seen starting at Lothagam had resulted in a modern-looking, grazing-dominated animal community.

  When we returned to Kanapoi in June of 1995 for our second season, I embarked on a large sieving enterprise in the face of near universal opposition from my crew. The year before, Ngui had spotted the two fragments of a lower jaw that I had instantly recognised as hominin. Nobody else—including Richard—believed me, however, thinking instead that they were bovid bones. This unprepossessing piece of jawbone showed only the outline of teeth that had broken off from the roots. Nevertheless, trusting my instinct, I hoped we would find more by screening the long shallow streambed that led down a gentle incline from where Ngui had found the fragments. All the sand in the channel had to be removed and sieved, which involved a great deal of arduous and tedious labour because the channel was more than sixty metres long. It felt as though the sieve would go on forever. Lasting more than six weeks with the whole crew wor
king on it for most of the time, this was one of the largest and most taxing sieves we ever did. Nevertheless, we were rewarded as more and more tiny fragments of jaw and teeth came out of the sieves. All my detractors and naysayers were silenced as it became apparent that I was right. Tiny fragment by tiny fragment, we pieced together a large unmistakably hominin mandible with enormous canine sockets that clearly must have belonged to a male. It dwarfed some of the other specimens we had found and led us to question whether it belonged to the same species as the others.

  * * *

  IN 1995, Alan Walker, Carol Ward, and I began to study both the Allia Bay and the Kanapoi material. Carol had been a student of Alan’s, and her chief interest was hominin postcranial fossils. We initially compared the specimens from Kanapoi with those from Hadar. When Don Johanson and Tim White had examined the Hadar collection in detail years earlier, they were surprised at how primitive and apelike the specimens were. In turn, we were surprised to find that the Kanapoi specimens were even more apelike than the Hadar ones in some characters. For example, the small piece of skull that preserved the external opening of the ear showed the ear to be extremely small, like that of a chimpanzee, and much smaller than any known from Hadar. The mandible that Nzube had discovered at the end of the 1994 field season was strikingly different from that of A. afarensis because it had almost parallel tooth rows like a chimpanzee or gorilla has. In addition, the outer surface of the jaw below the incisors (where modern humans have a chin) also differed. Similarly, when we compared the relative sizes of the canines with the sizes of the cheek teeth, the Kanapoi canines were larger and different in shape. The lower premolars immediately behind the canines (P3 and P4) were more primitive too.