By: Zhuoxun Jiang
In the book "The Descent of Man, and Selection in Relation to Sex", Darwin proposed the idea that the fossils of early humans would be found in Africa. He also hypothesized that we share a common ancestor with apes of Africa. Darwin's ideas would eventually lead to the creation of paleoanthropology. However, at Darwin's time paleoanthropology did not exist and his ideas were generally rejected.
Raymond Dart, a professor at the University of Witerwatersrand in Johannesberg, South Africa, acquired a skull of an early human found at a quarry in Taung, South Africa. In 1925, Dart named it Australopithecus africanus. During years of studying the fossil, Dart hypothesized that the species was in between humans and apes. His theory was widely rejected by the scientific community in the 1920s and it was not until the 1940s that Dart's ideas were accepted. This was one of the first discoveries of early hominid fossils.
After retiring from a career of medicine in 1934, Broom spent the rest of his life searching for early hominid fossils. Some of his most famous discoveries were in Sterfontein valley in South Africa. It was there in 1936 that Broom found the first adult Australopithecus africanus. Two years later in 1938, he found the fossils of another species of hominids he named Paranthropus robustus. That species showed a greater resemblance to apes than humans. Broom left the field in 1948 and devoted his last years of his life writing about his findings until his death in 1951.
In 1935, Mary Leakey joined his husband Louis Leakey in East Africa to search for early human fossils. They focused their efforts on the Olduvai Gorge in the Great Rift Valley of East Africa. They launched multiple expedition but it wasn't until 1959 they found their first hominid fossil. Today, it is known as Paranthropus boisei . Using new radiometric dating, Louis and Mary was able to determine that the fossil was 2-1.5 million years old. This was a breakthrough in paleoanthropology. Before this, scientists estimated that the earliest humans was less than 100,000 years old. Louis Leakey died in 1972. Mary would continue their research in the years after his death.
Between 1965 and 1983, C.K. Brain, another South African paleontologist, excavated the Swartkrans cave in South Africa for more fossils. The same cave was investigated by Broom years ago. Brain found thousands of bones of early humans. His findings shed light into the life of early humans. Brain's discoveries also suggested that the humans used primitive tools in the form of stones. Moreover, chewing marks on the bones suggested that those humans were victims of predators.
In 1974, a team of paleontologists led by Donald Johansen found another species of hominids in Northern Ethiopia. The species was classified as Australopithecus afarensis. It is one of the most complete fossil skeleton every found. It was a 40% complete skeleton of an adult female. The specimen was named "Lucy". Lucy stood 109 cm tall and weighed 27 kg. She was estimated to have lived 3.2-3.18 million years ago. The completeness of the skeleton gave scientists much more scientific data than any other fossils found.
In 1978, Mary Leakey and Tim White investigated the Laetoli site in Northern Tanzania. They found 59 footprints of bipedal humans, most likely that of Australopithecus afarensis. They were estimated to be at least 3.5 million years old. The footprints were characteristically human, not ape. Leakey estimated that the adults were between 124-145 cm tall.
In 1994, paleoanthropologist Ronald Clarke and colleagues found fossil fragments of a foot of an early hominid at Sterkfontein cave. After 4 years of investigating the cave, Clarke and his team nearly completed the fossil foot. Clarke named the specimen "Little Foot". Studies of the foot showed that it had some characteristics not found in other species of Australopithecus. Little Foot is one of the few complete fossils of early hominids. Subsequent investigations of the cave in later years revealed new bone fragments belonging to the same person and Little Foot. Excavations are still in progress to uncover more bone fragments. It is believed that the skeleton will be far more complete than Lucy.
In 2009, Tim White and his team released their discovery of an ape transitional species they named Ardipithecus ramidus in the Awash Valley of Ethiopia. It was dated back to 4.4 million years ago. Studies showed that this species might be the direct ancestors of Australopithecus afarensis.
In 2010, Lee Berger of the Unversity of Witwatersrand discovered two incomplete skeletons of a new species of early hominids he named Australopithecus sediba. The skeletons dated back to 1.977 million years ago. Further studies performed be Berger and his colleagues suggest that Australopithecus sediba may have descended from Australopithecus africanus and it could be one of the last links between genus Australopithecus and our genus Homo.