by Meave Leakey
That afternoon, we hurtled home from work in complete silence, each of us deeply engrossed in our own thoughts. Although driving slightly faster than his usual high speed, Richard was nevertheless dodging the potholes in the narrow road with characteristically surgical precision. Our drives were usually filled with careless talk about goings-on at the office, news of colleagues abroad, and the endless perplexing questions about particular fossils that make our shared profession at once all-consuming yet sometimes highly contentious and frustrating. But Richard was a million miles away from humdrum museum politics and fossil bones, and the silence in the car was pregnant with possibilities.
Ever the strategist and never one to turn down a seemingly impossible challenge, Richard was already mapping out his first one hundred days in office and beyond. My thoughts were of a different bent—how this appointment would fundamentally turn our lives upside down. Twenty years had passed since I had first set foot in Kenya in response to Louis Leakey’s ad in the Times—and nearly twenty years of a deeply fulfilling and successful partnership that had blurred the lines of work and play, home and office, husband and colleague so absolutely that the prospect of disentangling this perfectly meshed web that constituted our life together was quite simply impossible for me to imagine.
But the facts were unavoidable—Richard’s new appointment as director of wildlife meant that he could no longer coordinate the palaeontological fieldwork at Turkana. He would now have other interests, another life, and even further constraints on his time. With a deep pang of regret, I realised we were unlikely to ever again share those indescribable magical moments that come from working so closely together in the field with a shared passion.
My thoughts then turned to my mother-in-law and how Mary’s life had suddenly changed with her discovery of the australopithecine skull she called Dear Boy. With the increased funds and publicity resulting from this find, Louis no longer had the time to spend with her at Olduvai. Those halcyon years they had shared together were abruptly over. This may well have been on Mary’s mind too, for when Richard broke the news to her later that evening, she uttered a few choice and succinct words, then retreated behind a wall of stony disapprobation that lasted for many months. Mary, quite presciently, was deeply worried about what the appointment might mean not just for our family life but also for Richard’s safety and welfare. Later that evening, I called our teenaged children to tell them the news. At boarding school, Louise and Samira had been entirely shielded from the daily bombardment of press articles and had little inkling of how significant this would be to their lives. “Okay,” they said—and that was that.
Mary’s icy disapproval was not an option for me: Richard’s excitement was palpable and contagious. Under his directorship, Kenya’s national network of museums had burgeoned and had been running well for a number of years. He yearned for a new challenge. And I immediately recognised that with Richard’s appointment new doors might open for me too. Someone would have to take over the leadership of the field research, and I was in a prime position to do so. The only thing holding me back was an awareness of how big the shoes I needed to fill were—Louis, Mary, and Richard had built a formidable legacy. I couldn’t help but wonder if I was up to the challenge.
Yet, having digested the enormity of Richard’s career change, I couldn’t deny that there was a satisfying symmetry about the timing of all of this. Richard, a big-picture person, was most at home performing what other people would view as impossible tasks—finding Koobi Fora in the first place, exploring the gigantic spread of the Turkana Basin, raising the money and public profile we needed, and now, of course, turning Kenya’s severe poaching crisis around. In our partnership, I always tended to the minutiae—the details of parenting, studying the fossils, and penning the research papers with our colleagues.
Under Richard’s leadership, our work over the previous two decades had given us a good picture of the history of the Omo-Turkana Basin as a whole. Apart from the brief forays into the Late Miocene deposits during the early 1980s, we had concentrated most of our efforts on sites from the Late Pliocene and Early Pleistocene between two and one million years ago. This is relatively recent—a time when the human lineage had already long since differentiated from the ape lineage. But we had also identified a number of potentially important older sites and were at last beginning to connect the dots as to how disparate sites scattered around the modern-day lake relate to each other and reveal slices of time cut from a single geological sequence.
So perhaps the time was now right to change lenses, to zero in on a more micro level. At least another lifetime of exploration and discovery awaited me in near-virgin territory, palaeontologically speaking. I knew that each site might hold the secrets of different twists and turns in the story of our past. Wistfully, I acknowledged that I simply wouldn’t have the time to do it all. But where should I begin? In my mind’s eye, I reviewed what we then knew about the Turkana Basin and its geology, and thought that what I really wanted to explore was the earliest phases of human evolution—look for sites that predated all those we had been working in for the previous twenty years. But did those sites exist in Turkana?
* * *
THE OMO RIVER has drained the Ethiopian Highlands for millions of years, flowing southwards and leaving in its wake a thick floodplain of sediments rich with fossils. The secret to the Omo Valley’s perfection as a fossil site is the combination of these ideal conditions for fossilisation with repeated tectonic activity due to its location in East Africa’s Great Rift Valley. As a result, faulting cracks, uplifts, and tilts the beds of sediments so the older layers buried far beneath the present-day surface are exposed again. And periodic volcanic eruptions leave convenient layers of ash called tuffs in between the fossil layers, which can be easily and accurately dated.
In the past, the Turkana Basin didn’t exist. Some 4.2 million years ago, there was a great deal of volcanic activity and upheaval in the area, and we believe that this is what reshaped the landscape. As the Great Rift Valley was expanding, the earth’s crust became dangerously thin, causing it to weaken and sag, and this led to the formation of a depression. In the weakened area, a narrow zone about twenty-five to thirty kilometres wide, there was a great deal of tectonic activity. New faults appeared, and huge outpourings of magma led to the formation of sheets of basalt that can be seen today all over the basin.
The Omo River flowed into this new basin, and over thousands of years, sediments gradually filled the basin until the inflowing water overflowed the southern rim and the river again continued its path to the Indian Ocean. New subsidence and tectonic activity in the ever-active Great Rift Valley then deepened the basin further, and the process of filling with water and silt began anew. Thus, due to a combination of climatic fluctuations and tectonic activity throughout the last 4.2 million years, a river system has dominated the Turkana Basin while being superseded for short intervals by a lake collecting in the depression. This process is ongoing to this day.
Looking at the lake today, it is hard to conceive that it is an occasional presence, not a permanent feature. This succession of ancient rivers and lakes through time is the reason the Turkana Basin provides a lifetime of places to look for fossils—for all along the migrating lakeshore and river floodplains, animals were dying, and their carcasses were becoming fossilised and buried, with new tectonics later exposing them for us to find. These sediments are called the Omo Group deposits. They lie on top of sedimentary deposits that were laid down before the Turkana Basin was formed. These older sediments extend back for a staggering amount of time and include a few that are 165 million years old, where dinosaurs have been found.
Along the Omo River, the sediments in the Omo Valley are conveniently stacked up, and as a result, the fossil deposits they contain are easy to correlate in terms of their relative ages. Back in 1967, these immensely rich Omo sediments were thought to be very localised. The maps marked much of the rest of the Turkana Basin as “lava” barren of fo
ssils and therefore of little interest to palaeontologists. It was Richard who first noticed that the maps of the Turkana Basin were wrong. Much of the vast depression swathing 146,000 square kilometres is indeed devoid of fossils, but within this expanse, there are a number of pockets of sediments that are very rich in fossils. However, unlike in the Omo Valley, the sediments are not conveniently stacked up like a sandwiches on a tray. They are often many hundreds of miles apart. Compounding the challenges—although there are numerous ash layers from countless volcanic eruptions across the Turkana Basin—the volcanic horizons, so easy to spot in the Omo Valley, are often much harder to find and are not always present. And the same ash layer derived from the same volcanic eruption might look very different in two different locations, which makes it impossible to discern its identity through field observation.
While you have a whole proverbial elephant to look at in the Omo Valley, you might have only a trunk, a tail, or perhaps a toe in the rest of the basin. Putting the whole picture together and tying it back to the well-dated sequence in the Omo Valley proved to be almost impossible. Even when we did have a fossiliferous layer of sediments sandwiched between datable layers of volcanic ash, we could never be sure which of these tuffs derived from the same eruption, so we still could not correlate them with any certainty.
All we had to rely on for years were a series of maps that had been drawn in the 1970s when a professor from Iowa State University named Carl Vondra and his students came to Koobi Fora. Their interest was lithology—the waxing and waning of the lakeshore and river floodplains over the millennia—and they drew up a series of geological maps that we still use to this day. The shortcoming of these maps was that there was no way to tie them together securely and know if the lakeshore present in one area was the same age as that in another. Iowa State did not have a dating lab, so the maps had no dates associated with them. The only way we could guess at the correlation was to look at certain fossils that are really good age indicators because they change distinctively over time. The best of these are pigs, whose teeth have distinctly different characteristics according to the fossil’s age. By comparing the Turkana fossils to similar specimens from well-dated sites, it was possible to narrow down the likely age of our fossil sites. But the pigs provided only a rough date range.
Our current accurate understanding of the different ages of the sites around the Turkana Basin and our ability to relate them to one another is largely thanks to the tireless work of Frank Brown. Frank was a remarkable man—and a brilliant geologist to boot. Frank began his lifetime association with the Turkana Basin in 1967 as a young PhD student participating in the International Omo Research Expedition in Ethiopia, a joint affair between Kenyan, French, and American scientists led by Richard, Yves Coppens, and Clark Howell. When he came to work with us at Koobi Fora in the early 1970s, Frank already had a far greater understanding of the sequence of volcanic horizons than anyone else.
Frank’s genius was to develop a technique to analyse the ash layers for their chemical signature. It turns out that every single volcanic eruption, including different eruptions from the same volcano, has its own chemical signature, a unique composition of elements in the erupting magma and ash. This “fingerprinting” method finally gave us what we had long been looking for: a way to tie all the disparate groups of sediments in the basin to one another and the stacked sequence in the Omo Valley. Over decades of collecting ash samples from all over the Turkana Basin, Frank built a single picture of the area’s geology across a remarkably wide breadth of time.
Right around the time that I took over from Richard, one of Frank’s students at the University of Utah, Craig Feibel, also began to collaborate with us. He complemented Frank’s work by putting together a geological history of how the palaeo-environments changed in the last few million years. The sedimentary deposits laid down by river and lake systems carry a history of the particular environment that existed at the time. By being able to read these rocks, it is possible to reconstruct the habitat to a remarkable degree. Between these two great geologists, and others along the way, a relatively complete history of the changing habitat and climate of the Turkana Basin over four million years became possible decades after we found the first hominin skull in the riverbed at Koobi Fora.
* * *
“I’VE DECIDED WHERE I want to work,” I told Richard not long after his new job began. Richard, up to his neck in seemingly insurmountable problems, had very little time or inclination to think about fieldwork. Nevertheless, I was keen to bounce my ideas off him and tap into his experience leading a field exploration.
“I want to focus on the time when humans split off from the other apes.”
“Nobody has ever found anything at all at that age in Turkana. You probably need to do what I had already planned.”
“That’s exactly why I want to look!” I retorted.
Given the enormous and intractable poaching and mismanagement problems he was facing, Richard simply couldn’t generate any enthusiasm for my plans and was totally unable to share my excitement with me. Reluctantly, I realised that I was on my own in terms of making decisions and winning over the confidence of my inherited field crew.
I knew that the initial split between our ancestors, who walked bipedally, and those of the chimpanzee took place between six and five million years ago. This had been established back in the late sixties by Alan Wilson and Vince Sarich, who had literally counted the differences in the molecular composition of human and chimpanzee proteins to arrive at this relatively youthful time span. Proteins consist of long strings of amino acids, only some of which are vital to a protein’s structure and function. So it follows that mutations that change the structure of the nonessential amino acids will not affect the way a protein acts in the body and will therefore not be eliminated through natural selection. Because these mutations occur at fairly regular intervals, they are molecular equivalents of units of time. Wilson and Sarich thus arrived at an approximate measure of the amount of time that had passed since we set off on distinct evolutionary paths away from a common ancestor. Since this pioneering work, molecular clocks have become extremely sophisticated, and instead of proteins, scientists can work directly on the differences in our DNA sequence—our genome and even the ancient genomes of Neanderthals. But the main insight of Wilson and Sarich has not really changed: humans and African apes have been evolving along separate lineages for some six million years.
Richard was correct. In the two decades that we had been working at Turkana, neither our team nor anyone else’s had found any fossils to document this momentous evolutionary leap forward—the first apes to walk on two legs—or put forward the evidence for a sensible explanation as to why it happened when it did. Something monumental must have prompted this profoundly new evolutionary response in the human lineage that conferred an extraordinary advantage over previous adaptations. What this was and why it happened seemed to me to be the key to our subsequent evolution into the unique species that we are today.
I was more determined than ever to find that crucial evidence. Even more, I longed to crack the conundrum as to why it occurred. Charting the course of my research, I decided to hone in on that critical split between ape and human and work my way forward. From this great question, I knew that others would inevitably follow in a logical progression of currently unanswerable, deeply contentious questions right up to the birth of modern Homo sapiens. If I could answer any of these questions, then the answers would raise a slew of new questions of their own.
For that first season, my goal was to gain my team’s trust, cut my teeth as a leader, and identify which fossil site was most likely to yield the answers I was seeking. I knew I would need to prove my mettle fast. In this field, no fossils means no funding. I needed some important discoveries under my own belt to ensure that the project’s finances didn’t simply fizzle out under my leadership. Fortunately for me, I had been granted a vital window of opportunity: Richard had recently raised enough fun
ds for five years of fieldwork from the NOLS Outdoor Leadership Foundation and Amoco, which was exploring the Turkana area for oil. Five years on the job is a comfortable probation period—but fossil hunting is a treacherous, fickle business that relies heavily on luck.
I decided to begin on a set of exposures in West Turkana just south of the large seasonal Turkwell River. Since this was new territory, we had no aerial photographs; and procuring such photos entails a plane flying methodically back and forth to capture a grid of continuous images of the terrain below. Richard took our first set of aerial photos of East Turkana in 1970 on a shoestring budget. This was an uncomfortable and sweaty task for him as he perched with his camera above a small aperture that had been fashioned in the belly of the plane while Keith Mousley, a skilled bush pilot, flew back and forth, and kept the altitude and direction as steady as possible. At our first Koobi Fora camps, we all pored over the photos and patched them together to form a continuous area with only a few missing snippets of land. There are companies with specially adapted planes that do this for a substantial fee, and once we had the funds, we redid the East Turkana images professionally. But for the southern sites on the west side, I first needed to be sure that it was a justified expense.
Accordingly, I planned a series of quick survey visits to figure out the potential of the sites I was thinking of exploring. We would be based at South Turkwell, a site that we estimated could be 3.5 million years old. The steep and colourful cliffs bordering this stretch of the river make the forty-square-kilometre site a particularly stunning one and provide good relief on many outcrops—perfect for finding fossils. From Turkwell, short excursions would be possible to other promising sites. These included Loperot (an Early Miocene site where we hoped to find apes that lived some eighteen million years ago), Napudet (an extension of the South Turkwell exposures), Eshoa Kakurongori (a site that, like South Turkwell, might also give us early hominins), and Kanapoi (a slightly older site far to the south). I also planned to visit the site that most captured my imagination, Lothagam—an island of exposures that rises dramatically out of miles of low-lying, windswept desert plains between the Kerio and Turkwell rivers.