In 1859, when Charles Darwin first published Origin of Species in which the idea of natural selection was proposed as the driving force behind evolution, the data supporting his hypothesis came primarily from comparative anatomy and from fossil evidence. At this time, the science of genetics had not yet been born.
In 1860, Thomas Henry Huxley became “Darwin’s Bulldog” by presenting Darwin’s ideas at the British Association for Advancement of Science (BAAS). While promoting Darwin’s ideas about descent with modification (natural selection), Huxley publicly pointed out the close association between apes and humans. He postulated that humans and apes had a common ancestor. Since apes are found in Africa, it was also postulated that humans first evolved in Africa.
In 1871, Charles Darwin published Descent of Man which included humans in the theory of evolution. At this time, the fossil evidence documenting human evolution was rather limited and there was no evidence from Africa.
The scientific community soon embraced the theory of evolution through natural selection. During the twentieth and twenty-first centuries, more data accumulated which substantiated the theory and there was no data which showed it to be false.The data includes both findings from genetics, particularly DNA, and an increasing number of fossils.
Genetic and fossil data show that the human lineage and the ape lineage diverged 6-7 million years ago. The human lineage is characterized by bipedalism, that is, walking upright. The first humans—that is, the genus Homo—did not appear until about 2.5 million years ago. The four million or so years between the divergence from apes until the appearance of the first humans is shown in the fossil record in several bipedal species. The genus most likely to have given rise to Homo is Australopithecus. Tim White, in an entry in The Oxford Companion to Archaeology, writes:
“Australopithecus was neither an ape nor a human. All Australopithecus species had skeletons consistent with upright, striding bipedalism, and this unique hominid mode of locomotion is indicated in many parts of the skeleton.”
The first australopithecine fossil was discovered in 1924 at the site of Taung in South Africa. The following year, Raymond Dart named the species Australopithecus africanus and proposed that it was a bipedal species ancestral to humans. Subsequently, australopithecine fossils have been found at other sites in southern and eastern Africa. This genus, often seen as ancestral to Homo, lasted for about 4 million years. In general, there are two main types of australopithecines: gracile and robust. Leslie Aiello, in an entry in The Oxford Companion to Archaeology, writes:
“The main differences between these gracile australopithecines and the robust australopithecines is the large size of the jaws and teeth in the robust species.”
With regard to the division of australopithecines into robust and gracile divisions, Donald Johanson and Blake Edgar, in their book From Lucy to Language, write:
“For some, the robusts are best placed in the genus Paranthropus, which includes robustus, boisei, and aethiopicus, and sometimes crassidens. The nonrobust australopithecines are sometimes referred to as gracile australopithecines, probably a misnomer, since their bodies do not appear to be significantly more lightly built than those of the robusts.”
While the robust australopithecines appear to have been an evolutionary dead end, the gracile australopithecines were ancestral to the human lineage.
Like humans, the australopithecines were bipedal, that is, they walked upright. They looked a bit like upright chimps, standing only three to five feet tall and with flat nasal openings. The gracile australopithecines ate a diet of fruit, insects, seeds, roots, and possibly some meat. The robust australopithecines had larger jaws and back teeth which suggest that they had a diet which included coarse grassland vegetation. The massive jaw muscles of the robust australopithecines attached to a ridge on the skull.
With regard to the anatomical differences between apes and australopithecines, Tim White, in an entry in The Oxford Companion to Archaeology, writes:
“All Australopithecus species lacked the strongly projecting, pointed canines seen in the great apes. Another generic trait is the large size of the teeth relative to the body size, a phenomenon known as megadontia. This suggests that Australopithecus consumed low-quality foods requiring heavy chewing.”
In noting that australopithecines were bipedal but with relatively small brains, Tim White writes:
“Australopithecus is therefore a creature whose body had evolved toward the human condition considerably sooner than its brain did—a good example of ‘mosaic evolution.’”
In his concluding chapter in the Handbook of Human Symbolic Evolution, Charles Peters writes:
“These bipedal but ape-like earliest hominids were (by analogy with the more socially complex higher primates) probably readily capable of communicating their identity, location, emotional state, and probable intentions. It is hypothesized that the communication skill they may have possessed beyond that of extant apes was primarily gestural in modality.”
This gestural communication potential was made possible by the freeing of the hands with bipedality. On the other hand, there is no evidence that the australopithecines were physically capable of spoken language as they lacked a human-like vocal apparatus as well as a brain structure which could control speech.
Gracile Australopithecines
At the present time, several species of gracile australopithecines have been identified. These include anemensis (the oldest), garhi, afarensis, and africanus.
Perhaps the best-known australopithecine is Australopithecus afarensis. Found at sites in Tanzania and Ethiopia, afarensis has been the subject of popular TV programs and books. While most fossil australopithecine finds are known to paleoanthropologists by their catalog designations, A.L. 288-1 is known to the world as Lucy. Lucy is better known than her discoverer, Donald Johanson, and in their book From Lucy to Language, Donald Johanson and Blake Edgar write:
“Worldwide, Lucy has become an ancestral ambassador of sorts, acting like a magnet, drawing people to the study of human origins.”
With regard to Australopithecus afarensis, Donald Johanson and Blake Edgar write:
“This australopithecine, represented by nearly 400 specimens that include most cranial and postcranial bones in the body, is distinguished by a unique suite of primitive cranial, dental, and mandibular anatomical features. Overall the skull is very apelike in appearance, dominated by a strongly projecting face.”
In an entry in The Oxford Companion to Archaeology, Nicholas Toth and Kathy Schick report:
“Although upright walkers, these creatures still exhibit apelike features such as relatively long arms and curved phalanges, interpreted by some as arboreal adaptations.”
Australopithecus anamensis dates to 3.9 to 4.2 million years ago and many paleoanthropologists feel it may have been ancestral to afarensis.
One of the possible ancestors of our species (Homo sapiens) is Australopithecus africanus, a species which existed in Africa from about 3 million years ago until 2.3 million years ago. It had a brain size about one-third that of modern humans.
Paleoanthropology is a field filled with surprises and new discoveries which often lead to a revision in our perceptions of the past and human ancestry. One of these surprises emerged in the late twentieth century with a fossil discovery in Ethiopia which was named, appropriately, Australopithecus garhi (garhi means “surprise” in the Afar language).
This species appears to have flourished from 2.5 million years ago to 2 million years ago. The surprise is that it is associated with butchered bones which may indicate that it was eating meat. Donald Johanson and Blake Edgar report:
“The discovery, however, of antelope bones bearing stone tool cut marks and even hammerstone impacts demonstrate that hominids were processing animal carcasses for meat or marrow.”
In addition, there are some stone tools associated with garhi. It appears that they were transporting raw stones and perhaps stone tools to places where the carcass was processed. Donald Johanson and Blake Edgar suggest:
“…it was precisely this behavioral change that stimulated and supported brain enlargement: tools preceeded big brains, big brains did not preceed stone tools.”
A number of paleoanthropologists see garhi as ancestral to Homo. Donald Johanson and Blake Edgar write:
“While A. garhi is temporarily positioned between A. afarensis and early Homo, not all scholars accept that it was ancestral to our own genus. A. garhi may simply be a side branch on the human family tree that evolved megadontia (large teeth) in parallel with the robust australopithecines.”
Robust Australopithecines
At the present time, paleontologists and paleoanthropologists generally identify three species of the robust australopithecines: aethiopicus. (the earliest known robust australopithecine), boisi, and robustus (found at the cave deposits of Swartkrans and Kromdraai, South Africa).
Aethiopicus was first named in 1968 from a fossil found in southern Ethiopia. The species appears to have flourished between 2.7 and 2.5 million years ago.
Paranthropus boisei is a robust australopithecine which had a gorilla-like skull and powerful chewing muscles. The first specimen of this species was found at Olduvai Gorge in northern Tanzania. In their book From Lucy to Language, Donald Johanson and Blake Edgar write:
“The specimen was nicknamed ‘Nutcracker Man’ because of the enormous teeth.”
This species, while related to modern humans, is not considered a human ancestor. This species flourished from 2.3 million years ago until 1.2 million years ago.
When first discovered by Mary Leakey in 1959, this fossil was named Zinjanthropus boisi. It was later classified as Australopithecus boisi and finally to Paranthropus boisi, indicating that it is not a human ancestor.
More Paleoanthropology
Ancient Humans: Fire
Ancient Humans: Neandertal Language?
Ancient Africa: How Old Is It?
Ancient Humans: A Short Overview of Homo Ergaster
Ancient Africa: A Short Overview of Homo Habilis
The Ancient World: An Overview of Homo Erectus