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— Phil Campbell
— Oren S. Harman
C. K. Brain
In the early twentieth century, the prevailing view was that humans had originated in Eurasia. In 1925, the first evidence of an early fossil link between the apes and man was published, and Africa was proposed as the cradle of humanity. This bold claim was largely dismissed at the time. But with further finds, especially in the eastern part of the continent, Africa has since remained at the center of the search for human origins.
In 1924, the fossilized skull of a child, half-ape, half-human, found its way without warning into the hands of a young anatomist in Johannesburg, South Africa. He was in an excellent position to interpret it and, in the subsequent paper in Nature, to challenge the accepted concepts of the time. This man was Raymond Dart; his insight shows the value of the prepared mind.
In 1923, Dart and his wife Dora traveled from Britain to South Africa, where Dart was to take up a new post. He was thirty years old and not enamored of the prospect. He later recalled, "I hated the idea of uprooting myself from what was then the world's center of medicine [University College, London] ... to take over the anatomy department atJohannesburg's new and ill-equipped University of the Witwatersrand. I felt I had lived a pioneer's life for quite long enough in my younger days." But what was to happen there the following year was surely beyond his wildest dreams.
Dart wished to establish an anatomical museum in his new department, and his attention was drawn to fossilized baboon skulls that were being unearthed in a lime mine at Taung in the northern Cape. In Adventures with the Missing Link, Dart relates how two boxes of fossils from Taung were delivered to his house one Saturday afternoon in 1924, just as he was dressing for a wedding reception to be held there. Unable to contain his curiosity, he wrenched open the boxes in the driveway. The first did not seem to contain anything of interest. But when he looked into the second, he later recalled:
a thrill of excitement shot through me. On the very top of the rock heap was what was undoubtedly an endocranial cast or mold of the interior of the skull. Had it been only the fossilised brain cast of any species of ape it would have ranked as a great discovery, for such a thing had never before been reported. But I knew at a glance that what lay in my hands was no ordinary anthropoidal brain. Here in lime-consolidated sand was the replica of a brain three times as large as that of a baboon and considerably bigger than that of an adult chimpanzee. The startling image of the convolutions and furrows of the brain and the blood vessels of the skull were plainly visible. It was not big enough for primitive man, but even for an ape it was a big bulging brain and, most important, the forebrain was so big and had grown so far backward that it completely covered the hindbrain. But was there anywhere among this pile of rocks, a face to fit the brain? I ransacked feverishly through the boxes. My search was rewarded, for I found a large stone with a depression into which the cast fitted perfectly.... I stood in the shade holding the brain as greedily as any miser hugs his gold, my mind racing ahead. Here I was certain was one of the most significant finds ever made in the history of anthropology. Darwin's largely discredited theory that man's early progenitors probably lived in Africa came back to me. Was I to be the instrument by which his 'missing link' was found? These pleasant daydreams were interrupted by the bridegroom himself tugging at my sleeve. 'My God, Ray,' he said, striving to keep the nervous urgency out of his voice. 'You've got to finish dressing immediately-or I'll have to find another best man. The bridal car should be here any moment'. Reluctantly, I replaced the rocks in the boxes, but I carried the endocranial cast and the stone from which it had come along with me and locked them away in my wardrobe.
For the next three months Dart used every spare moment to patiently chip away the matrix from the skull, using his wife's sharpened knitting needles. Then, two days before Christmas, the rock parted and the face of a child emerged, with a full set of milk teeth and its permanent molars in the process of erupting. Dart wrote: "I doubt if there was any parent prouder of his offspring than I was of my Taungs baby on that Christmas of 1924."
Dart wasted no time in preparing his report for submission to Nature. In essence, it pointed out that while the skull, teeth, and jaw of this child had been "humanoid," rather than anthropoid or apelike, this was undoubtedly a small-brained hominid, or member of the human family-the first of its kind to be described. He pointed out that the forward position of the foramen magnum, where the spinal cord attached to the skull, clearly indicated that this hominid had walked upright, with its hands free for the manipulation of tools and weapons in an open environment far to the south of the equatorial forests inhabited by chimpanzees and gorillas. Finally, Dart asserted that Australopithecus africanus, the southern ape of Africa, as he called it, provided clear evidence that Africa had been the cradle of mankind.
Although Charles Darwin had predicted that human ancestors must have lived in Africa, subsequent finds of large-brained fossil humans in Europe had swung scientific opinion in favor of Eurasia as the birthplace of humanity. These included numerous Neanderthal remains, those of the modern-looking Cro-Magnon man from the Dordogne region of France, discovered in 1868, and the Piltdown skull from southern England in 1912, whose large brain and apelike jaw fulfilled the expectations of the time-until it was shown to be a hoax. In fact Piltdown had seemed far more acceptable than had Pithecanthropus (now Homo) erectus, a fossil hominid with a relatively small brain but upright stature whose remains were found in 1893 by Eugene Dubois in river gravels of Java after a five-year search. The reception this discovery received was so disappointing that Dubois locked the remains away for twenty-five years in a Dutch museum before they became available for others to study.
So it is not surprising that Dart's child from Taung, presented as the "missing link" from Africa, met a chilly reception in Europe. The authorities dismissed it as, at best, a relative of the chimpanzee or gorilla with little relevance to human ancestry, stressing that until an adult specimen was available, the matter was hardly worth discussing.
This attitude prevailed even though Dart took the specimen to Britain in 1931 and exhibited it at scientific gatherings. At this time, the Taung child had a strange experience: by mistake, Dora Dart left it in the back of a London taxi. After a prolonged tour of London, the box was opened by the taxi driver who, alarmed at seeing a skull inside, took it straight to a police station. Here a distraught Dora was reunited with the child.
Although Dart's claims endured severe criticism overseas, in South Africa they enjoyed the unwavering support of Robert Broom, a paleontologist known for his work on the evolution of mammals from reptiles. In his later years, while he was based at the Transvaal Museum in Pretoria, Broom started a deliberate search for an adult fossil of Australopithecus. His attention was drawn by several of Dart's students to the Sterkfontein caves near Krugersdorp, where lime mining had unearthed fossil baboon skulls as at Taung.
In August 1936, on his second visit to Sterkfontein, Broom was handed the endocranial cast of an adult ape-man by the quarry manager and in the next few days he found much of the rest of the skull. One month later his report on Australopithecus transvaalensis, as he named the new find, appeared in Nature and The Illustrated London News. The initial discovery was followed by many others during the next few years, leaving no doubt as to the hominid status of this African ape-man.
Not content with this, in 1938 Broom described a second kind of hominid from the nearby cave of Kromdraai as Paranthropus robustus, with a wide flat face and extremely large molar teeth. Subsequent work has shown that this "robust" ape-man lineage arose from an africanus-like stock about 2.5 million years ago and then coexisted with early humans until about a million years ago, when it became extinct.
With fossils of adult ape-men now available for study, Dart's concept of Australopithecus as an African ancestor of later humans was generally accepted. Heartened and relieved, Dart reentered the emotional field of hominid paleontology and started a long-term investigation of the Makapansgat Limeworks cave, 250 kilometers northeast of Johannesburg. Here miners had blasted out a vast accumulation of fossil bones, and among them Dart identified and described several new Australopithecus specimens. Most of the other fossils came from antelope and Dart speculated as to how all of these bones had found their way to the cave. In a long series of publications he argued that the ape-men had been mighty hunters that underwent a "predatory transition from ape to man," bringing back to their cave those bones from their kills that could serve as useful tools and weapons. Using dramatic and provocative prose, Dart presented his view of "the blood-bespattered archives of humanity" and provoked further research on the ways that bones accumulate in African caves.
East Africa came into the paleontological spotlight in 1959, when Mary Leakey found a very complete robust ape-man skull at Olduvai Gorge, Tanzania; this has been followed by numerous other finds in Tanzania, Kenya, Ethiopia, and elsewhere. Many of these fossils come from lake bed sediments, which can be dated from the volcanic ash beds laid down with them. It appears now that more than four million years ago, small upright-walking hominids such as Ardipithecus ramidus and Australopithecus anamensis were living in forest-edge habitats of northeast Africa; in time they were succeeded by small Australopithecus afarensis individuals, known now by many fossils including the skeleton of "Lucy" immortalized by Don Johanson. These appear to have been the ancestors of Dart's Australopithecus africanus, which could have given rise to both our own and the robust ape-man lineages.
Today paleoanthropology is a rapidly evolving field. New discoveries and interpretations confirm Africa's place as an evolutionary center. Attention has lately shifted to Chad, in the central part of the continent, with the announcement of the discovery of a six to seven million-year-old hominid skull there. But Asia should not be ignored, as the latest evidence of early Homo erectus technology in Japan and China has emphasized. Moreover, fossil discoveries are now not the only way to investigate human origins: molecular techniques, which involve the tracing of our ancestry through analysis of genetic material in living humans, and even in Neanderthals, provide a further tool. Dart would be delighted with the expansion of his vision.
Excerpted from A Century of Nature Copyright © 2003 by The University of Chicago. Excerpted by permission.
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|Chronology of twentieth-century science|
|1||Raymond Dart and our African origins||1|
|1925 / Australopithecus africanus: the man-ape of South Africa|
|2||Electrons make waves||21|
|1927 / The scattering of electrons by a single crystal of nickel|
|3||The atom completed||37|
|1932 / Possible existence of a neutron|
|4||Superfluidity: a new state of matter||49|
|1938 / Viscosity of liquid helium below the [lambda]-point|
|5||From nuclear physics to nuclear weapons||61|
|1939 / Disintegration of uranium by neutrons: a new type of nuclear reaction|
|6||The double helix||73|
|1953 / A structure for deoxyribose nucleic acid|
|7||Dawn of structural biology||85|
|1958 / A three-dimensional model of the myoglobin molecule obtained by X-ray analysis|
|8||The first laser||105|
|1960 / Stimulated optical radiation in ruby|
|9||The quasar enigma||115|
|1963 / 3C 273: a star-like object with large red-shift|
|10||Seafloor magnetism and drifting continents||129|
|1963 / Magnetic anomalies over oceanic ridges|
|1968 / Observation of a rapidly pulsating radio source|
|12||Viruses reverse the genetic flow||165|
|1970 / RNA-dependent DNA polymerase in virions of RNA tumour viruses|
|RNA-dependent DNA polymerase in virions of Rous sarcoma virus|
|13||Images of body and brain||187|
|1973 / Image formation by induced local interactions: examples employing nuclear magnetic resonance|
|14||Journey to the T cell||201|
|1974 / Restriction of in vitro T cell-mediated cytotoxicity in lymphocytic choriomeningitis within a syngeneic or semiallogeneic system|
|15||Molecular switches for "animal electricity"||215|
|1976 / Single-channel currents recorded from membrane of denervated frog muscle fibres|
|16||DNA sequencing: the silent revolution||231|
|1977 / Nucleotide sequence of bacteriophage [Phi]X174 DNA|
|17||The blueprint of animals revealed||259|
|1980 / Mutations affecting segment number and polarity in Drosophila|
|18||A hole in Earth's shield||281|
|1985 / Large losses of total ozone in Antarctica reveal seasonal ClO[subscript x]/NO[subscript x] interaction|
|19||Carbon cages and carbon tubes||299|
|1985 / C[subscript 60]: buckminsterfullerene|
|20||Seeking other solar systems||313|
|1995 / A Jupiter-mass companion to a solar-type star|
|1997 / Viable offspring derived from fetal and adult mammalian cells|