The Sediments of Time

by Meave Leakey

  But what if the climate hadn’t swung back again? If the dryer spell had persisted, perhaps the small-beaked finches would have become extinct. Might a new giant-beaked finch have taken its place on the famous family tree of thirteen Galápagos finches? This was the scenario at Lothagam between seven and five million years ago. There were extreme fluctuations in climate with dramatic swings between wetter and dryer times, the evidence for which we see today in the changing nature of the ancient river deposits of the Nawata and the Apak. But there was also an inexorable drying trend—the conditions never fully swung back. The implications of such a change were enormous and far-reaching—there would have been ramifications all the way down the food chain as new habitats and feeding opportunities presented themselves and were exploited by new species.

  If, as the evidence suggests, a major radiation of C4 grass species replaced many of the previously dominant herbs and shrubs, this would have created a large number of new feeding niches. Thousands of species of grass-eating animals, both large and small, would have followed. Although we find mostly large animals in the fossil record, this change would primarily have affected the many smaller creatures, including caterpillars, butterflies, beetles, birds, lizards, frogs, and many others whose remains would have decomposed before fossilisation could occur. But this radiation of new grass-eaters would have created new feeding opportunities for both omnivores and carnivores higher up the food chain—including our own ancestors. This could be the elusive catalyst that we had been searching for that might have stimulated a radiation of early human ancestors exploiting new open-country habitats and these new food resources.

  To my enormous frustration, we found tantalizingly little evidence of hominins at Lothagam in spite of the abundance of other fossils. At 3.5 million years, we found two whole teeth and two fragments of teeth. After intensively searching for four seasons, we found only two more isolated teeth dated somewhere around five million years during the crucial Upper Nawata times. At this same age, there is the lower jaw fragment found by Patterson’s team in the 1960s, but this specimen is too incomplete to assign taxonomically to either ape or human with any certainty. But there is no evidence whatsoever for hominins in the older sediments at the bottom of the Nawata—and I had chosen Lothagam specifically because this was the time frame where I desperately hoped to find them.

  We can, nevertheless, speculate that, like the other fauna, these early hominins were exploiting the upheavals in the food chain to take advantage of new rich dietary opportunities. For instance, we know from the tooth morphology of more recent and better-preserved, hominins that early human ancestors probably ate fruits, insects, birds’ eggs, and sometimes small mammals. But at five million years, when they first appear in the record at Lothagam, did they walk on all fours like an ape? Or were they the first intrepid explorers who stepped out of the trees on two legs?

  * * *

  BECOMING BIPEDAL is the pivotal event that enabled further evolutionary changes that set humans apart. No longer bound to the physical demands of walking quadrupedally, the forelimbs were free for other tasks, and this enabled the development of a dexterous hand over time. Manual dexterity vastly improved the efficiency with which an individual could gather food, enabling even a young infant to easily put berries and other hard-to-reach foods in its mouth—but, crucially, it also allowed for further developments later on, such as the manufacture of effective stone-tool kits and the ability to carry and store foraged food. All of these improvements in food uptake are what eventually enabled human ancestors to grow larger brains, which are among the most calorie-expensive organs in the body. Thus, bipedality was the key adaptation that led to the divergence of the ape and human lineages. Such an altered landscape does proffer the incentives for a momentous alteration in ape locomotion to an upright stance. However, without the fossil evidence, I could only conjecture that the sweeping changes in all the other fauna would have affected the apes too.

  Modern apes are not very good at walking on the ground on all fours. For example, modern chimpanzees, who walk on their knuckles, expend some 35 percent more calories getting from A to B on the ground than a similarly sized quadruped such as a large dog. So it is probably not very surprising that they traverse the ground for less than a mile or so each day. But the changing habitats we were witnessing in the vista of Lothagam’s geology must have significantly reduced the available forest cover in East Africa, gradually transforming the landscape into the mosaic of floodplain savannas dissected by gallery woodland along the rivers.

  A consequence of such a widespread reduction in forest cover would have been a significant decrease in foraging opportunities in the forests. If our early ancestors were arboreal and moved on the ground inefficiently like modern apes, then the ability to better cover open ground would have had vast potential benefits. Moving into the newly evolved grasslands would have dramatically increased their foraging opportunities, but these earliest hominins would still have needed to be able to retreat rapidly back into the trees to escape dangerous carnivores. Thus, as forest area gradually diminished, there would have been a strong selective advantage to moving efficiently in the increasingly wide-open spaces—in other words, to walk bipedally.

  So why were we not seeing any hominins in Lothagam before the five-million-year mark? I could think of only two possibilities. It simply couldn’t be that my team had missed the evidence, after searching so hard. They were too good for that. One possibility was that the hominins first evolved to suit the new landscape somewhere else and only colonised the area around Lothagam at about five million years. After this time, we begin to find increasing evidence of their presence elsewhere in the Turkana Basin. The other possibility was that they were at Lothagam all along but only in small numbers because they were prey to voracious carnivores that kept their population small and that scavenged most of their remains. Maybe the evidence is now all but gone even though the hominins were there.

  There were indeed several large and ferocious predators during the Nawata. The carnivore I found in that scorching bend of the river on our very first 1989 survey is a good example. When we excavated this specimen, we unearthed a near-complete skeleton of an animal similar to a wolverine. This would have been a fearsome, strong, and muscular predator. There were also several species of sabre-toothed cats at Lothagam that would have made easy pickings of ape-sized prey. The most common of these cats is well-known from another skeleton that we first spotted in 1990 while walking up the dry sandy bed of the River Nawata. All that was exposed on the surface were several foot bones encased in extremely hard rock that were barely protruding out of the cliff face high above us. A large part of the base of this cliff had broken off and provided a wall that protected the fossils from being washed away by fast-flowing floodwaters whenever it rained. In 1992, we excavated and sieved the sediment that was trapped by this wall. We were rewarded with many bones of the skeleton as well as some broken pieces of the skull.

  This made us even more certain that we would find more remains if we could follow the hand bones into the cliff with an excavation. But how could we do this? It would mean erecting scaffolding, removing the top of the cliff, and digging into the hard rock. In 1993, Alan Walker supervised this challenging excavation. What was most interesting about this leopard-sized felid was the large claw on the forepaw that presented a formidable cutting weapon. When Lars Werdelin eventually studied the skeleton, he gave it the name Lokotunjailurus emageritus, a name derived from the Turkana words for “cat” and “claw.”

  This sabre-toothed cat would certainly have given the early hominins at Lothagam good reason to fear exposure on the ground. A possibly even more serious threat was Dinofelis, a similar-sized felid with a smaller canine and less specialised chewing teeth that crops up throughout the Nawata and Apak members. All in all, there must have been strong evolutionary incentives to risk becoming an easy meal by leaving tree cover.

  Numerous theories have been put forward to explain the strat
egic change in the locomotor pattern of our ancestors to bipedality. The new stance permitted a greater variety of sexual and aggressive displays, and allowed our ancestors to see over high grass and other vegetation. Hard-to-reach foods that were unavailable to competitors could be accessed from the higher vantage point of two legs: by standing upright, our earliest ancestors could have reached farther to pick fruits, berries, and seeds and search for insects or pluck eggs from birds’ nests. Strong seasonality was a feature of the weather patterns at this time, and seasonality leads to times of food scarcity. Individuals that had access to more food in times of drought would have had a strong selective advantage (witness the change in a few generations of finches on Daphne Major). Adaptations to avoid falling prey to the formidable assembly of carnivores must have played their part as well. Moving upright allowed early humans to regulate their body temperature by reducing the surface area exposed to the hot African sun—but this thermoregulatory advantage only kicked in once they were above a certain height. In all likelihood, it was most probably a combination of many factors that led to the evolution of bipedality in human ancestors. These theories are hard to prove, but it is likely that feeding was a key factor and that the opening of new feeding niches through habitat change was a significant driving force.

  Even without much evidence of the hominins I badly hoped to find, Lothagam was a palaeontologist’s paradise. It gave us a remarkably comprehensive snapshot of a period in our prehistory that was hugely significant in our evolution. Over the course of five years, we found fossils that provided an exquisitely detailed faunal record, and we deciphered the geology and the corresponding evidence for habitat change, which must surely have played a key role in opening new feeding niches for the earliest hominins to exploit.

  But in spite of all this, I was on the clock, and I was running out of time. My five years of funding were nearly up, and I badly needed to find some of our ancestors. Our donors like “sexy” finds, and none of the fabulous wealth of knowledge we gained at Lothagam was headline-grabbing material. “Mass extinctions seven million years ago; forests turn to grass” really didn’t cut the mustard! (Although now, given that a new wave of extinction is upon us, this might be an easier story to sell.) There are few alternative sites of a similar age in Kenya, and none of them are as richly fossiliferous as Lothagam. I therefore began to consider sites close to Lothagam of a slightly younger age, hoping that one of these might shed further light on the emergence of bipedality. But as I pondered where to go next, I was interrupted by another huge setback in our personal lives that would change things forever.

  7

  Nine Lives

  Wednesday, June 2, 1993, dawned much like any other day in the field. We wiped away the remnants of our breakfast and set off into the exposures of the Apak member just as the flies awakened and the last tinges of pink and orange faded from the sky. I shook off the unpleasant vestiges of a bad dream that, unusual for me, I could still remember in the morning. Just before the field season began, I bought Richard some new fancy swimming fins to use when we went snorkeling during our regular holidays to our home in Lamu on Kenya’s northern coast. They were bright yellow and black, and he really liked them—but in the dream, he couldn’t use them because he hadn’t any feet. I am not superstitious, and I don’t believe in prophetic dreams. I only remembered this peculiar and unpleasant coincidence long after the horrors of the days to come when I was back in Nairobi gazing miserably at these gaudily cheerful pair of flippers.

  The morning passed with nothing more remarkable than the discovery of a nice horse tooth. I busied myself at one of the carnivore excavations after lunch. But later in the afternoon, the droning hum of a distant plane materialized into something completely unexpected—a KWS aircraft buzzing the camp to alert us of its imminent arrival at the airstrip. My heart sank into a leaden ball in my stomach; only bad news could have brought the plane here. Communication through the radiotelephone was extremely inefficient, and more often than not, we failed to make contact with Nairobi. If anyone had to get a message to us in a hurry, the only sure way was to fly into camp. The first shivers of premonition had me rushing to the car and over to the airfield. Premonition turned into outright alarm as I saw the KWS chief pilot, Phil Mathews, and another pilot and good friend, Sacha Cooke, climbing out without Richard and lifting worried faces towards me.

  It turned out that Richard’s engine had cut out on a short flight to Naivasha, and he had crashed his plane over a thick forest. He had managed to find one small clearing to land but had snagged a large mango tree as the plane glided headlong toward the tiny gap in the trees. He was alive, as were his passengers, Phil and Sacha reassured me, but they told me that I must immediately return to Nairobi. All they would say is that he had a broken leg and a broken nose. I rushed back to camp to gather a few belongings and scribble a note to Kamoya, and I was soon on my way back to Nairobi.

  Phil and Sacha remained tight-lipped, but as I pried a few more details out of them and news filtered through over the KWS radio, the accident began to sound more and more serious. Yet I still could not bring myself to believe that Richard might be badly injured. Time and again he has been likened to a cat with the proverbial nine lives, getting himself out of seemingly impossible situations and reaffirming my deep-rooted faith in his ability to survive. This wouldn’t be any different, I told myself firmly, as the fault lines of the Rift Valley unfolded far too slowly below us. Arid dusty plains gradually changed to steep escarpments and then, at long last, to the green patchwork of fields and dotted huts on the fertile highlands that give way to the development on the outskirts of Nairobi. The familiar landmarks had never, ever passed this slowly before.

  We finally landed just before dark, and I rushed into the hospital as Richard was about to be whisked away into surgery. The surgeon spoke to me as he scrubbed up, briskly informing me that both Richard’s legs were severely damaged although he did not think there were other serious injuries. No, I couldn’t see Richard yet. “Go home,” he advised. He was planning to clean the wounds that were still full of earth and grass. I could phone the hospital or come back in four hours as they certainly wouldn’t be through with the surgery before that. Hugely frustrated at not being able to see Richard or learn the true extent of his injuries, let alone make any informed decisions for him, I reluctantly left and went to see Mary at her home in Langata before rushing home to relieve Sacha, who had been valiantly manning the phone that was ringing off the hook.

  When I finally got to see Richard later that night as he was being wheeled back from the operating theatre, I was shocked. He was in intensive care, his face a swollen mess, and his head and legs heavily bandaged. At least I could be thankful that his lungs, ribs, kidney, and spinal cord were undamaged. His four passengers had varying and relatively minor injuries but none as serious as Richard’s, but his bodyguard did have a broken arm. Richard had already been given a blood transfusion, which worried me as the hospital had not asked us for blood. Although the blood was screened, I would have preferred them to use blood from a close friend or relative as is common practice to this day in the country given the high incidence of serious diseases like HIV. Infuriatingly, my own blood, correctly typed and safe, was sitting unused in the hospital’s blood bank! I had donated some as a contingency for Joyce Poole, an elephant researcher, neighbour, and close friend of Richard’s, who had given birth shortly before this.

  At last, the doctor came to talk to me about Richard’s injuries. He didn’t mince any words. He blandly described Richard’s right leg as “pulp” and added that both his ankles were very badly broken. His left foot had been dislocated, and many of the nerves had been severed. During the surgery, the doctor had put a screw into the left talus (anklebone) to stabilize it and removed dead bone from the right leg. I was thankful at least for my anatomy training as I could follow the full extent of these horrible injuries. The next couple of days confirmed my initial perception—that the doctor’s bedside manner
was simply dreadful. Adding to my worries, a number of people privately expressed doubts about his being the right surgeon to tackle Richard’s injuries and strongly urged me to get a second opinion. As I questioned people further, it became evident that there were tensions between this doctor and other members of the medical team. While none of the medics questioned the doctor’s ability, they clearly did not get along well. I had deep qualms about whether the team could keep a patient’s best interests paramount if they were not sharing information with one another but constantly bickering. Then the hospital—and the whole country—ran out of the pain-killing drug Pethedine (Demerol). Richard was incredibly sick and he was in unspeakable pain. For the second time in our married life, our fate was in the hands of doctors and nurses, and in Richard’s sheer determination to persevere against the odds.

  The days passed in a slow-motion blur. We turned away a constant stream of visitors and fielded endless phone calls that Richard was far too sick to take. Flowers from well-wishers piled up outside the door as they couldn’t be brought into the sterile IC unit, and we sent them on to other patients. As they had more than a decade earlier, friends and colleagues rallied around, even offering to raise money to help offset our mounting hospital bills. Richard’s brother Philip and I privately consulted with Dr. David Silverstein, a well-respected and prominent physician at the hospital who was also the president’s private doctor. He was emphatic that he would seek the best trauma centre in the world if he were in our shoes—and that the level of care and expertise was simply not high enough in Nairobi to treat Richard’s extensive injuries.