The Sediments of Time

by Meave Leakey

  Richard threw himself into learning how to walk and amazed the nurses with his tenacity and the speed with which he was up on his temporary new legs. “I used to be a master on stilts as a boy. It is like riding a bicycle—once you have learnt, you do not forget how,” he told them, brushing off their praise and modestly playing down the huge challenges he had overcome. By October 26, he was back in Nairobi walking unassisted on his permanent prosthetics. He passed his medical and went flying on November 12. Life slowly returned to “normal” or perhaps to a new “normal.” Richard was determined to see past his disability, and because he did, others soon saw him as he sees himself, undiminished and fighting for what he believes with determination and grit. Richard resumed his hectic schedule at KWS, and I began to plan my next field season. The wheelchair was relegated to collect dust in the attic, where it would sit for decades. But if his new career had cast doubt on our ever working together again in the field, the accident made this possibility even more remote. We never spoke of it, but beneath cheerful façades, we both deeply mourned all that was lost that fateful day the plane came down.

  8

  A New Early Biped

  “I’ve decided that we are going to Kanapoi next,” I announced brightly to Richard one morning. Much as I expected, his response was a mere grunt. Some rather inauspicious incidents had firmly prejudiced him against the site, but my gut instinct was to give it a go.

  Richard had first attempted to survey Kanapoi in 1985. He and Alan Walker had flown into a makeshift airstrip near the site, where they met up with Kamoya, Nzube, and Wambua Mangao to survey the area on foot. Wambua, like Kamoya and Nzube, first worked for Mary at Olduvai before joining Richard’s team in the early 1970s. Wambua is a quiet, solid, and very strong man with an uncanny ability to find the most beautiful and completely concealed specimens. The trio had cut across country from the excavation of the Turkana Boy many miles to the north and had worked hectically since early morning to ready the airstrip and build a temporary camp. The construction of the airstrip proved more difficult than expected, and they were already weary by the time Richard arrived. He immediately marched them off on an extensive and exhausting search of the exposures. Their weariness only intensified as mere scraps of fossil bone were all that could be found. Worse, Alan was feeling very off-colour, and by midafternoon, Richard realised that he needed medical help and decided to fly back to Nairobi before dark.

  Kamoya recalled that he had never felt so worn out in his life when, caked in a chalky layer of fine dust, they returned to the camp they had hastily erected that morning. The plan was to continue surveying for a couple of days. However, their efforts came to an abrupt halt that very same day when a group of bandits sauntered into camp. This in itself was not enough to warrant undue alarm since armed men frequently passed through. Although they often positively bristled with an assortment of battered weapons that probably dated back to World War II, they were usually content to move on after filling their bellies with a good hot meal, fresh water, and some strong sweet tea. They were interested in stealing livestock or carrying out revenge attacks, not interfering with a curious collection of outsiders scrabbling around and intently scrutinizing rocks. But on this day, Kamoya noticed that the local youths employed as camp help were unaccountably nervous and flighty. The boys spoke the same language as the interlopers, and when Kamoya pressed them, they nervously admitted that they had overheard plans to do rather more than share a meal with the team. Under the keen eye of a group of armed men with malicious intent, what could be done?

  Outnumbered and unarmed, Kamoya opted to wait for the cover of darkness. They carried on their usual activities as casually and unselfconsciously as possible. The traditional mancala board game bao was played, cigarettes were smoked, tea was served, firewood was cut, and dinner made. The minutes and hours dragged painfully by. When night finally fell, they left the food conspicuously on the fire until the last possible minute as they slashed the guy ropes holding up their tents and surreptitiously gathered what belongings they could in the darkness. Then they piled everything and everyone into the car, and tore out of camp as fast as possible, a scalding hot pot of goat stew bouncing at their feet.

  As a result, Kanapoi remained a question mark over the years. Whenever Richard and I had occasion to fly over the site on our way farther north, my questions were invariably dismissed. Apart from the fact that Richard had spent very little time surveying there, I had other reasons to hope for better things from Kanapoi: Bryan Patterson, of Lothagam fame, had also been to Kanapoi some thirty years earlier, and he had found a hominin humerus in 1965. On our own brief survey of Kanapoi in 1989, we had not even begun prospecting when Wambua called out to stop the car and pointed to what looked like one of the large boulders marking the edge of the road—it was a complete and beautifully preserved elephant mandible. If Richard and the crew had not found anything, it did not necessarily mean that there was nothing to find—I now suspect that on top of having scarcely any time to look for bones, Kamoya and the team were also looking in the wrong place. The fossil layers at Kanapoi are extremely localised. Indeed, years later, I would ask Kamoya, Nzube, and Wambua which of all the sites they had surveyed did they think would be the most worth returning to. “Kanapoi,” these three veterans of the hunt instantly replied in unison.

  The deposits at Kanapoi contrast greatly with those at Lothagam even though Kanapoi is only about fifty-five kilometres away. Where Lothagam is all treacherous steep slopes and eroded canyons, its ancient rocks sculpted into all manner of curious shapes in a kaleidoscope of rich reds, greens, and browns, Kanapoi’s deposits are much gentler in incline and lighter in tone, with buff shades of grey, brown. and white brightly reflecting the sharp desert sun. It is correspondingly less hot. Our camp was set attractively under shady acacia and palm trees on the banks of a small tributary sand river called the Atalomeyan. Conveniently situated in the middle of the exposures, it allowed us to walk to work most of the time, saving precious fuel. And there was good drinking water just a few miles from our camp as Christian missionaries had installed a hand-operated water pump in the nearby village of Kaesamalit. A mere flick of the wrist to turn a large wheel brought forth the miracle of pure, delicious water! To top it off, the site was also several hours closer to Nairobi and accessed by a relatively good road.

  The only drawback was that the last part of this road, a dirt track leading east from the tarmac trunk road from Nairobi, crossed some fairly large seasonal rivers, including three crossings of the broad, meandering Kalabata River close to camp. The dreadful drought that characterized our time at Lothagam ended while we were at Kanapoi, and on more than one occasion, we made the thirteen-hour journey from Nairobi to find the Kalabata in full spate.

  This happened the very first time I made the trip, with Samira, at the beginning of the first field season in 1994. We crossed the river once with ease. It was flowing but not deep. Halfway across the second crossing, the river deepened, and we suddenly found ourselves in dangerous fast-flowing water. It was too late to reverse, so we kept going and had one nasty moment when we were not sure we would make it safely across. At the third crossing, the river was unquestionably deep and flowing fast. In my mind’s eye, I could picture the car tilting and sinking into the sandy, muddy bottom—water running through the doors and getting into the fuel tanks—before rolling over and being swept downstream. No. Heavily laden with supplies, it would be folly to try to cross. There was nothing for it but to settle down and wait patiently for the river to recede. In the gathering darkness, we set a stick in the riverbank to mark the water level, and then snacked on the remnants of our lunch. We laid down our kangas, the brightly printed rectangular cloths that Kenyan women put to any number of uses, and wrapped up against the mosquitoes while the level of the inky water dropped inch by inch through the night.

  All in all, however, conditions at Kanapoi were far easier than at Lothagam—and when the first hominin came in at the end of only the sec
ond week of work, morale shot up. Wambua found this first treasure—a lovely piece of upper jaw (maxilla). It came from an individual who lived to a ripe old age and had worn its teeth down through years of chewing to the point that you couldn’t tell too much about it. This precious fossil was also covered in matrix that would have to be meticulously removed once we got back to the lab in Nairobi, a process that takes endless days of patient work with an air drill under a microscope. Nevertheless, after five long years of painstaking searching at Lothagam that yielded only a paltry collection of isolated teeth, some of the men were starting to doubt their ability to find respectable hominins at all. Wambua’s success injected new determination and a healthy spirit of competition back in the crew. And I allowed myself to hope that Kanapoi would indeed have more of the hominins that Lothagam had so sorely lacked. Having persuaded the National Geographic Society to give us a grant for that first year at Kanapoi, I was desperate to find some hominins to ensure that the organization would continue to fund the project.

  We didn’t have long to wait. We put some of the crew to sieving the surface material around Wambua’s maxilla while others continued to prospect. The sieve turned up several other identifiable fragments of hominin, including the other side of the recently discovered upper jaw. This was the first of many sieves we conducted at Kanapoi—and they were some of the biggest and most tedious sieving jobs we did anywhere because the gently sloping topography had scattered the fragments over a huge surface area.

  What would turn out to be the most significant find of the season did not come from a sieve, however, and it came at a most inopportune time: on the first day of a very brief and rushed visit from Craig Feibel when Kamoya and I had planned to devote ourselves exclusively to studying the geology with him. We had invited Craig to do the Kanapoi geology after the fantastic job he did at Lothagam, but he was working at Koobi Fora that season and could get away for only three days, which was barely long enough for him to show us the lay of the land. So we had very little time to gain critical initial geological insights. As we stood on the side of a small buff while Craig studied the topography, Kamoya casually pointed to the ground between us. “Look at that nice piece of tibia,” he said, understatedly. Both of us immediately thought that it might be hominin—but bones that look like hominin tibiae have a nasty, disappointing habit of turning out to be something else altogether. The tibia Kamoya had discovered was the proximal (top) end, with the articular surface (the top of the bone that fits with the bottom end of the thigh bone) quite severely eroded, which made it even harder to identify. It also seemed to be implausibly big. So I replied equally casually, “Mmm. Very nice. We must be sure to return to collect that some other time.” We built a little cairn and took careful mental note of where we were.

  For the rest of Craig’s visit, Kamoya and I privately pondered the piece, saying nothing to anyone, while we learnt as much as we could about the geology of Kanapoi. In camp, we found ourselves furtively poring over the cast of another tibia found more than two decades earlier. It was a great deal smaller than the piece we had marked with the cairn on the hillside. But there was no mistaking the strong resemblance. The plane arrived to pick up Craig from an airstrip at Lokori, a small village to the south, just as he finished hastily scribbling some notes and diagrams for us that would faithfully guide us through the rest of the field season. We thanked him, waved good-bye, and watched the little plane recede hazily into the distance. Then we rushed back to the exposures to collect the piece of tibia and bring it back to camp to study properly. The whole crew unequivocally pronounced it hominin!

  The cast we compared our tibia to belonged to Lucy, who was discovered by Don Johanson at a site called Hadar in Ethiopia. Don, like many others, had cut his teeth in the Omo Valley as a student and later had the great fortune to be invited to Hadar by Maurice Taieb, a French geologist who had noticed the richness of fossils littering the site. Taieb’s invitation established Don in one of Africa’s especially rewarding sites—Lucy is one of the most spectacular hominin finds of all time and all the more remarkable for her 3.2 million years of age. With what Johanson estimated to be 40 percent of her skeleton intact, including valuable diagnostic bones like the pelvis and femur, she was the most complete example of any species of early hominin found at the time. This may not sound like much, but to a palaeontologist, such completeness is nothing short of miraculous, the sort of thing dreams—and careers—are made of. A veritable mine of information was contained in her ancient remains. Furthermore, Don’s other discoveries at Hadar, including the remains of multiple individuals he dubbed the “first family,” provided an astounding wealth of additional evidence about this early species, Australopithecus afarensis.

  Not much of Lucy’s skull was found, but there was enough to show that her brain was tiny—estimated to be comparable in size to that of a modern ape’s—and her jaw was more V-shaped than our own U-shaped one. Far more telling were Lucy’s well-preserved hip and leg bones, essential in the interpretation of locomotion. They left no doubt that she was bipedal. In a quadruped, such as a modern-day chimpanzee, each hind leg descends vertically from the hip socket to feet placed quite far apart on the ground. But in bipedal locomotion, this arrangement would cause the centre of gravity to shift wildly on each supporting hind leg, making for clumsy and inefficient steps and the side-to-side “wobble” that chimpanzees have. In humans, the femoral shaft is angled relative to the condyles (knee-joint surfaces), and below the knee, the tibiae descend straight to the ground. This “carrying angle” between the long axes of the femur and the tibia allows the centre of gravity to move forward in a straight line as we walk. Simply put, bringing the knees closer together than the hips is what allows the biped to balance on one leg at a time without waddling or toppling over while striding forward.

  Lucy’s distal femur and tibia exhibited this carrying angle just like modern humans do. To prevent the knee from dislocating due to the angle of the leg shaft, there is a prominent lip on the patella (kneecap). The condyles are large and the bony shaft is robust, so the limb bone is built to withstand the added strain of bearing weight on just two limbs. The pelvis has also evolved to accommodate an upright stance and the need to balance the trunk on only one limb with each stride forward. The talus (anklebone) shows evidence for a convergent big toe, which increases efficiency in bipedal locomotion (at the expense of agility and gripping power in the trees). And Lucy’s vertebrae share our spinal curvature, which is necessary for a permanently upright stance. This intriguing picture laid to rest a long-running debate about the sequence in which the key adaptations that define human evolution appeared. Contrary to the views long held by some palaeontologists, bipedalism evidently fully developed long before any evidence of enlarged brain capacity.

  Becoming bipedal is the pivotal adaptation that set humans apart from other apes (not drawn to scale).

  For all these human traits, Lucy was also very primitive. Although she was certainly moving bipedally, her body proportions were quite different from ours. Standing only about one metre tall, she had a long trunk and long arms relative to the length of her legs. Her long torso and arms, her rather short legs and broad pelvis, and her somewhat curved fingers and toes strongly suggested to me that she retained considerable agility in the trees. This school of thought is not one that everyone agrees with, however. Some scientists assert that the morphology suited to tree climbing is a relic from her past and that she was fully bipedal and never retreated to the trees.

  In 2000, long after we had left Kanapoi, a new fossil find near Hadar would shed light on this very question in the form of a juvenile A. afarensis from Dikika. This gorgeous specimen includes an almost perfect skull with its brain cast still enclosed and much of its skeleton. It took many years for its finder, Zeresenay Alemseged, to clean the brittle, priceless bones. They included the complete scapula, a real rarity because this bone is so delicate that it is almost never preserved and found. The scapula looks remarkably like t
hat of a gorilla’s—and not at all like ours. Another fragile bone was also preserved—the bony labyrinth of the inner ear. We use our bony labyrinth for balance, which means that it looks very different in bipeds than it does in quadrupeds. This telltale bone also strongly suggested that A. afarensis had the ability to move through the trees.

  These features support our hypothesis that the earliest bipeds would still have sought refuge in the trees from time to time in order to escape the many dangerous predators that shared their environment. A. afarensis was both a bipedal and an arboreal ape—with a very different locomotor repertoire from that of modern humans.

  Don Johanson found Lucy in Hadar, Ethiopia, in 1974 (and gallingly for us, the very day after Richard, Mary, John Harris, and I visited Johanson and Maurice Taieb’s camp to see some of their initial discoveries). Mary was working at Laetoli on the edge of the Serengeti plains at the time, where she had recovered fragmentary remains of a human ancestor similar to those from Hadar. Her team would also make a momentous discovery in 1976. Unlike the extensive barren badlands of Hadar and Turkana, the sediments at Laetoli are exposed only in limited eroded areas as much of the site is covered in tall grasses and thick stands of acacia. These were frequented by bad-tempered Cape buffaloes and were rich with other game, which together supported such an inordinate population of ticks that they needed to be brushed off several times a day rather than picked off individually. Mary also remarked on the extraordinary number of deadly and highly camouflaged puff adders around camp as well as the “considerable nuisance” made by elephants chasing members of her team away from their work. In spite of these menaces, it was to the elephants that Mary would owe the most remarkable discovery of her career.