Hominine Fossils and Paleoarchaeologists
Until the 1950s, European scientists believed that Homo sapiens evolved in Europe, or possibly in Asia, about 60,000 years ago. Since then, excavation of fossil bones in East Africa, pioneered by Mary and Louis Leakey, has revealed that Homo sapiensmay have emerged in Africa much earlier.
The skeleton of Lucy © Alain Nogues/Sygma/CORBISHuman Origins
Most scientists agree that the human species emerged somewhere in Africa about 200,000 years ago. This understanding is based on fossilized bones and skulls that have been uncovered in East Africa and dated accurately by radiometric dating. These bones and skulls range from 25,000 to 4.4 million years old and show many different stages of human and primate evolution. These fossils have been uncovered by paleoarchaeologists — scientists who study the material remains of the entire human evolutionary line.
Based on the fossil evidence, paleoarchaeologists currently tell the following story: For 99.9 percent of our history, from the time of the first living cell, the human ancestral line was the same as that of chimpanzees. Then, about 5–7 million years ago, a new line split off from the chimpanzee line, and a new group appeared in open savanna rather than in rainforest jungle. The old group in the rainforest continued to evolve, and two of its species remain in existence: the common chimpanzee and the bonobo.
The new group in the savanna evolved over the millennia into several species (how many is not entirely clear, but at least 18 different ones), until only one was left: Homo sapiens. All the species before us back to our common ancestor with chimpanzees are now collectively called “hominines.” (They used to be called “hominids.”)
Try visualizing it like this. Imagine your mother holding hands with her mother, who is holding hands with her mother, and keep going back in time for 5 million years. The final clasping hand would belong to an unknown kind of an ape whose descendants evolved into chimpanzees, bonobos, and, ultimately, your mother. If we count each generation as averaging 14 years, there would be about 360,000 hand-holders in the hominine line. (Thanks to Richard Dawkins, a contemporary English biologist, for this metaphor.)
Paleoarchaeologists debate what names to put on the bones they find. They have to decide which ones ought to be considered a separate species. No central authority determines this, so paleoarchaeologists discuss it and try to reach a consensus. They more or less agree on three main categories of species before Homo sapiens; these areAustralopithecus (2–4 million years ago), Homo habilis (1.8–2.5 million years ago), andHomo erectus (2–.4 million years ago). Clearly, some of these species must have overlapped during hominine evolution.
What scientists now know took many years to figure out. The first early human fossil bones were found in Europe — Neanderthals in Germany in 1857 and Cro-Magnon in France in 1868. Java Man was found in Sumatra, Indonesia, in 1894. Most paleoarchaeologists in the 1920s and ’30s felt certain that Homo sapiens must have evolved in Europe, or possibly Asia, since a group of fossils known as Peking Man was found in China in 1923–1927. Africa, widely known then as the “Dark Continent,” was not considered a possibility largely due to racist thinking.
Louis Leakey measures an ancient skull found in Tanzania. © Bettmann/CORBISThe Leakeys Look to Africa
When did anyone start looking in Africa for hominine fossils? One German professor found a Homo sapiens skeleton in 1913 in Tanganyika (now Tanzania), and a professor in South Africa found a child’s skull there in 1924. But archaeologists denied that these bones were significant. The first to make credible finds were an English couple, Louis and Mary Leakey.
Louis Leakey was born and grew up in Kenya, in a tiny mission village nine miles from Nairobi, now the capital of Kenya but then a small village on the railroad to Lake Victoria, the source of the Nile River. Louis’s parents were missionaries from England. They hired English tutors for their children, but mostly Louis spent his childhood hunting and trapping with the local Kikuyu boys. Louis spoke Kikuyu as a native language and went through initiation rites with his Kikuyu peers. At the age of 13 Louis built his own house, as was Kikuyu custom. He also found some relics that he recognized as ancient hand axes, even though they were made of obsidian rather than flint, like the ones in Europe were. World War I prevented Louis from being sent to boarding school in England; he was 16 before he traveled to London to prepare for entrance to Cambridge University to become an archaeologist.
Mary Nicol grew up in England, but her father was an artist who took his family traveling for nine months out of each year, mostly in southern France, where he painted pictures that he sold in London. He loved Stone Age history and showed Mary many archaeological sites in France. She was only 13 when he died, and her mother sent her to strict Catholic schools in Lon- don, where Mary rebelled and was temporarily expelled several times. At 17 she took charge of her own education, learning to fly a glider and to draw, and attending lectures in archaeology.
Mary and Louis met in London in 1933 when she was 20 and he 30. Louis was married at the time — with one small child and another on the way — but he and Mary nevertheless began an affair, and in 1935 she joined him in Tanzania during one of his expeditions. They married the following year once his divorce was complete, though Louis’s actions cost him his research fellowship at Cambridge University.
Louis Leakey © Jonathan Blair/CORBISLouis chose the Oldowan Gorge, now called Olduvai Gorge, as his main area of research. It lies about 200 miles southwest of Nairobi, in present-day Tanzania. Olduvai Gorge took shape when a river cut through the sediment that had formed over 2 million years at the bottom of a huge ancient lake. About 20,000 years ago an earthquake drained the lake; after that, the river cut a deep gorge through the sediment of the old lake bed. The river sliced mostly through the shoreline of the lake, revealing the remains of people and other animals that had once gathered there. Almost 2 million years of history are exposed in the 25-mile-long main gorge and in a side gorge 15 miles long, a “layer cake of evolution,” as Virginia Morell, a biographer of the Leakeys, calls it.
Mary and Louis Leakey studying skull fragments © Bettmann/CORBISOlduvai Gorge lies in the Great Rift Valley, a massive geological fault in the African plate. The fault line runs from the Red Sea southward through Ethiopia and Tanzania, down to the mouth of the Zambezi River, in Mozambique. Eventually this crack in the plate will deepen so much that the eastern piece of Africa will break off and move away. Mountains and volcanoes frame the edge of the Great Rift Valley. The volcanic eruptions produce ash, which easily buries and fossilizes bones, making this ideal territory for finding fossils. After being buried under layers of soil for millions of years, the fossils are moved upward as the Earth continues to shift.Life in the Field
Life was an adventure for Louis and Mary at Olduvai and other sites in the Great Rift Valley. They lived in tents or mud huts with dirt floors and kerosene lamps. Often they had no fresh vegetables or fruit, living on fresh fish, canned food, rice and corn meal, and coffee and tea. (They both smoked cigarettes heavily.) Sometimes Louis shot a gazelle for its meat. Prides of lions prowled their camps at night. Keeping the cars and trucks running in the wilderness proved a monumental task. On occasion the only water available came from watering holes where rhinoceroses wallowed; the soup, coffee, and tea would taste of rhino urine. African servants cooked and served their meals and washed their clothes.
The Leakeys’ reward came in living outdoors amid some of the most beautiful scenery in the world — gorgeous volcanic mountains with the Serengeti Plain spread out before them, hosting flamingos, rhinos, giraffes, lions, leopards, antelope, and zebra. The couple worked early and late in the day to avoid the hottest sun, in sand that radiated heat. They used a dental pick and an artist’s brush to reveal, ever so slowly, the hidden fossils of long ago, buoyed by the excitement of finding clues to how humans came to be.
Louis and Mary found many ancient tools and fossils of extinct animals, but finding human fossils proved more difficult. In 1948 Mary found a primate skull that they thought might be the “missing link” connecting apes and humans, but it turned out not to be. In 1959 Mary discovered a skull that dated at 1.75 million years old, a find that made the Leakeys famous and led to funding from National Geographic. In 1960 Louis found the hand and foot bones of a 12-year-old, whom he named Homo habilis, thus classifying this species of hominine.
Until the 1950s fossil hunting was filled with confusion because no one had a way to date the bones except by estimating the age of the rocks in which they were found. Every expedition had to have a geologist to study the layers of rock, but even those scientists were just approximating the age.
Things changed that decade with the advent of radiometric dating, which allowed fossil ages to be identified much more accurately. Carbon-14 atoms would not work for dates that go as far back as early hominines; instead, potassium found in the volcanic ash was used in a potassium-argon radiometric-dating technique.
Louis Leakey was convinced that humans had evolved from the apes, which he realized were fast losing their territory in Africa. They had never been studied in the wild, only in captivity. Since knowing more about them would provide insights into hominine behavior, Leakey took the initiative to raise funds for people chosen by him to study apes in their own habitat before it was too late. He looked for young women who could do this work. In 1960 he helped a young Jane Goodall begin her study of chimpanzees in the wild; later, Dian Fossey studied gorillas and Biruté Mary Galdikas studied orangutans.
Finding Lucy
Meanwhile, others had begun searching for fossil bones in Africa. After Louis Leakey died of a heart attack in 1972, Mary Leakey continued working at Olduvai Gorge; however, the next spectacular find occurred in the Ethiopian part of the Great Rift Valley, at Afar. In 1974, Donald Johanson, an archaeologist from Case Western Reserve University in Cleveland, Ohio, found parts of a skeleton there that dated back 3.2 million years — the oldest hominine bones yet discovered. Johanson nicknamed the skeleton “Lucy,” because that night, as he and the others in camp celebrated their discovery, they listened repeatedly to the Beatles’ song “Lucy in the Sky with Diamonds.”
Lucy was assumed to be female because the bones were of a small hominine, roughly 31⁄2 feet tall. Only about 20 percent of a full skeleton was found, and most of the skull was missing. Fragments suggest it was small, while the foot, leg, and pelvis bones showed that Lucy walked upright. This was important evidence that, in the human line, bipedalism came earlier than brain growth, which previously had been supposed to come first.
Anthropologist and author Donald Johanson© Bettmann/CORBISThe Leakey Legacy
Mary and Louis Leakey raised three sons, who lived with them in the field — Jonathan, Richard, and Philip. These sons stayed in Kenya as grown men, and Richard carried on his parents’ work on human origins, making his first major find in 1972. After discovering another significant skull, he went on to build up the National Museum of Kenya and to run the Kenya Wildlife Service, focusing on saving elephants.
After Louis’s death in 1972, Mary became a leading scientist in her own right. She initiated a camp at Laetoli, 35 miles from Olduvai, where the soil dated to 3.59–3.77 million years old. There, in 1976, she found an astonishing set of hominine footprints preserved in volcanic ash, more evidence that hominines of that time walked upright.
Mary Leakey received honorary degrees from many universities, including Oxford, Yale, and Chicago. She lived at Olduvai long enough to see leopards and rhinos dwindle to near extinction. In 1983 she ended her fieldwork and moved to Nairobi, where she died in 1996 at age 84. Her granddaughter Louise Leakey, daughter of Richard and Meave Leakey, carries on the Leakey tradition, working in the scorching sun to piece together the story of human origins in Africa.
Thanks to the pioneering work of Louis and Mary Leakey, there’s overwhelm- ing evidence to back that story. Confirmed by recent genetic testing, it is clear that Homo sapiensoriginated in Africa — much longer ago than previ- ously thought — after separating from the chimpanzee line 5–7 million years earlier. The Leakeys spent their lives digging in the earth and tirelessly raising funds in the search for human origins. At a time when few others could entertain the thought, Louis demonstrated that our species had its beginnings on the African continent.
By Cynthia Stokes Brown
For Further Discussion
Think about the following two questions and respond to them in the Questions Area below.
- What are some of the reasons scientists prior to the Leakeys believed that humans originated in Europe or Asia?
- How did their discoveries lead to both scientific and social changes?
Sources
Bowman-Kruhm, Mary. The Leakeys: A Biography. Amherst, NY: Prometheus Books, 2010.
Johanson, Donald C., and M.A. Edey. Lucy: The Beginnings of Humankind. New York: Simon & Schuster, 1981.
Morell, Virginia. Ancestral Passions: The Leakey Family and the Quest for Humankind’s Beginnings. New York: Simon & Schuster, 1995.
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