Stephen P. Broker
1.
Australopithecus africanus
(The South African apeman)
In 1924 at a limestone quarry at Taungs, Cape Province, South Africa, workers exposed what has been described as the greatest fossil find ever made. The discovery consisted of two interconnecting rock fragments which, on examination revealed the forward part of a skull, and much of the lower jaw of a previously unknown form. A natural endocast of the braincase also made up part of the find. Found by chance during mining operations for the Northern Lime Company, the humanlike character of the skull was recognized by the quarry foreman in charge of the blasting, M. deBruyn. The two rock fragments were eventually delivered to Dr. Raymond Dart, a physician and professor of anatomy at Witwatersrand University in nearby Johannesburg.
Raymond Dart spent more than four years working on the fossil skull. He eventually freed the lower jaw from the enclosing rock matrix, exposing the surfaces of a complete set of milk teeth, as well as the first permanent set of molar teeth. The molars were just in the process of erupting, suggesting that the ancient owner of the
s
kull
was
a young child of about five or six years.
The Taungs child, as it came to be known, showed characteristics which contradicted thenprevalent notions of the appearance of man’s early ancestors. With a relatively large jaw and a brain capacity estimated at 405cc., or midway between that of the common chimpanzee and gorilla of today, the Taungs child appeared apelike to most contemporary scientists. What seemed contradictory was that the fossil teeth were clearly human in appearance, though they were larger than the teeth of modern man at the same age. The creature was not large brained and largejawed, as would have been expected.
Dart’s description of Taungs, which he named
Australopithecus africanus
—the South African apeman—and his subsequent speculation about Taungs’ humanlike brain structure and probable tool use were generally regarded as fallacious notions by his colleagues. Taungs was explained away as an aberrant and pathogenic form of man. Not until related finds were made at Sterkfontein, Swartkrans, Kromdraai, and Makapansgat in nearby regions of South Africa, by Robert Broom and John Robinson, was Taungs accepted as an important PlioPleistocene find.
The site of the fossil discovery at Taungs has long been destroyed by mining operations. Because of the absence of material suitable for absolute dating, the age of
Australopithecus africanus
from Taungs must be regarded as unknown. Few fossil faunal remains were found in association with the skull. There are no stone tools from this site. By comparing the Taungs skull with A. africanus remains subsequently found at the other South African sites, however, the age of the Taungs infant is now roughly estimated at 1.8—0.8 million years B. P. which makes it a latesurviving member of the species. This is in spite of the fact that Taungs is the type specimen for
Australopithecus africanus
.
Australopithecus africanus was probably an omnivorous form, feeding on plant materials such as seeds, nuts, berries, and roots, as well as on occasional insects and other small animals. This is the species of australopithecine described as gracile (slight), with a moderatelysized jaw and no prominent bony ridges on the skull. It has recently been described as o
ccurring in East Africa, as well. Australopithecus africanus
specimens thus far found suggest that the species remained relatively unchanged in Africa for more than 2 million years, from approximately 3 million to perhaps less than 1 million years ago.
2.
Homo erectus
(
Sinanthropus pekinensis
—Chinese man from Peking, or Peking Man)
The Taungs baby was discovered by a quarryman and it was fortuitously turned over to Raymond Dart, an anatomist who was willing to discard prevalent notions of how early hominids must have appeared. Circumstances for the discovery of
Homo erectus
fossils in China were considerably more involved.
Traditional peasant drugstores in China were known to carry “dragon bones,” in jars of fluid. These dragon bones were rocklike bones which, when ground to a powder, were used for medicinal purposes. They were often, in fact, the fossilized remains of prehistoric and extinct forms of life. Scientists in this century have at times made pilgrimages to the Chinese drugstores, looking for fossil hominid remains. By asking questions of the local people, the sources of the fossils have sometimes been determined. In this fashion, the fossilbearing limestone quarries of Chou Kou Tien, near Peiping, China, were discovered by the scientific community.
In 1926 two obvious human teeth were discovered at Chou Kou Tien. The discoveries were announced by Dr. J. Andersson, a Swedish geologist, and by Davidson Black, a Canadian who was an anatomy professor at Peking Union Medical College (Rockefeller Medical College of Peiping). The following year an international team was organized to conduct a thorough dig of what proved to be a large ancient cave, which had gradually filled in with sediment. Key scientists involved in the project were Black, who died in 1934, his successor Franz Weidenreich, a German scientist, Pei Wenchung (W. C. Pei) of China, and Pere Teilhard de Chardin of France.
The fossil teeth were assigned to a new generic category,
Sinanthropus
. With the specific name
pekinensis
, these fossils were known as Chinese Man from Peking. By 1928 the skull of a child was unearthed at Chou Kou. Tien, and in a twoday period in November, 1936, three more skulls of Peking Man were found. During ten years of digging, blasting out, and sifting rock, from 1927 until 1937, remains of 30 to 40 individuals were unearthed. Although few postcranial bones were found, the excavation turned up individual teeth, mandibles, and a total of five wellpreserved skulls. Strong evidence for use of fire (charcoal fragments) and for tool use (pieces of quartz not native to the area) was also obtained.
The advent of World War II brought a halt to the fossil excavations. Scientific study and political realities clashed headon in 1941, when Japanese troops invaded and occupied China. The Peking Man fossils were crated up with the intention of sending them to the United States for safekeeping, but in December of 1941, shortly after the United States entered the war, it became known that the fossils were lost. Though the fate of the fossils has to the present remained a mystery, in recent years the nature of their disappearance has become more clearly understood. During the Japanese occupation of China, Japanese troops confiscated the boxed fossils, while imprisoning the U.S. Marines who were responsible for safekeeping of the fossils. In the course of moves from one prison camp to another, it is likely that most of the fossils were discarded by the Japanese troops as being of no value, At the conclusion of the war, a few of the less important remains were recovered in Tokyo, suggesting to some people that the possibility still exists that other Peking Man remains will again be recovered.
Prior to the outbreak of the war, a number of excellent casts were made of the Peking skulls; they, along with drawings and very complete descriptions of the finds, were brought to America by Weidenreich. In the postwar period, excavations at Chou.Kou.Tien began again, and new discoveries have been made. Consequently, although most of the original material has been lost, valuable information does exist about the fossils.
Peking Man is characterized by a large cranial capacity, 9001200 cc. Along with the evidence for his use of tools and fire, the large brain size suggests that Peking Man was indeed an earlier form of human. The Chou Kou.Tien fossils are of the same type as some fossils found in 1891 in Java by Eugene Dubois, a Dutch physician. Dubois had set out to discover the remains of early humans and within a year had succeeded in locating a skull cap and thigh bone near the Solo River in central Java. They were given the name
Pithecanthropus erectus
, and they were more commonly known as belonging to Java Man. Java Man and Peking Man have since been reclassified as
Homo erectus
, using Dubois’ species name but recognizing that the remains are of an earlier form of human. Other
Homo erectus
remains have more recently been discovered in East Africa at Olduvai and Lake Turkana. Louis Leakey’s Olduvai specimen, known as O.H. (Olduvai Hominid) 9, was found in association with stone handaxes, and it is dated at 490,000 years B.P. The skull found by Richard Leakey at Koobi Fora, Lake Turkana, Kenya, labeled as KNMER (Kenya National MuseumEastRudolph) 3733, is an extremely wellpreserved specimen having a cranial capacity of 800 cc. This skull has been dated to 1.6 million years B.P., considerably earlier than any previous finds. Current estimates for the age of Peking Man indicate that he lived 500,000 to 300,000 years ago, with the younger age being more likely. Java Man is judged to be several hundred thousand years older.
Homo erectus
was a wideranging species, found throughout parts of Africa and Asia, a species which persisted for perhaps 1 1/2 million years. In addition to a cranial capacity about twothirds modern size, the species is characterized by a very thick skull which is flattened in mandible, and large teeth. The postcranial skeleton is quite similar to that of modern man, with a fairly robust pelvis.
Homo erectus
may have been as tall as 5 feet, weighing perhaps 175 pounds.
3.
Ramapithecus punjabicus
(Rama’s ape)
While the scientific community was regarding Dart’s South African apeman with considerable skepticism and sharing the public enthusiasm for the ongoing discoveries near Peking, a Yale University graduate student named G. Edward Lewis was searching elsewhere in Asia for fossil hominoids. A paleontologist for the Yale North India Expedition examining the Simla Hills badlands, Lewis collected in 1932 a series of fossils including a right maxilla with premolar, molar, and portions of incisor and canine teeth intact. This specimen, numbered YPM (Yale Peabody Museum) 13799 and presently housed with the Peabody collection in New Haven, was assigned the name
Ramapithecus brevirostris
(Rama’s shortspouted ape) by Lewis. Rama is a mythological prince in an Indian epic poem. The species name has subsequently been changed to
punjabicus
, a name appearing earlier in the literature describing similar fossil forms. YPM 13799, which may well have been purchased by Lewis in India, is the type maxilla specimen for
Ramapithecus
. It shows that
Ramapithecus
had reduced canines and incisors, cheek teeth with thickened enamel, and that it probably possessed a short face, all characteristics found in the family of man, Hominidae.
A number of additional ramapithecine fossils have since been described. In 1961, Louis Leakey discovered 14millionyearold fragments of two maxilla and a lower molar of a form he named
Kenyapithecus wickerii
, after Kenya Colony and the man who first located the site at Fort Ternan, Kenya, where the fossils were unearthed, Fred Wicker. In the 1960’s Elwyn Simons and David Pilbeam, both then of Yale University, examined a number of fossil specimens housed in museums around the world, and they reclassified approximately two dozen fragments as belonging to the ramapithecines. Their work suggested that
Ramapithecus
, a likely descendant of the Myocene ape
Dryopithecus
, was the earliest known ancestor of man, and that it represented the first evolutionary steps away from the pongid line.
During the 60s and 70s, Pilbeam led expeditions to the Siwalik Hills badlands of northern Pakistan, searching for further ramapithecine remains. In March, 1975 and January, 1976 team members made surface recoveries of four bone fragments which fit together to form the most complete mandible yet recovered. The mandible shows that
Ramapithecus
did not have a parabolic, human like dental arcade, as originally thought, but rather a Vshaped, more apelike arcade. Though the shape of the arcade is not now regarded as one of the more anatomically important characters,
Ramapithecus
is no longer granted the high status that it once received. Pilbeam now favors consideration of four major groups, the dryopithecids, ramapithecids, pongids, and hominids, and he avoids models of phylogeny that suggest direct linear descent of one fossil form from another.
Although numerous fossil fragments of ramapithecines have now been recovered from parts of Hungary, Turkey, Greece, India, Pakistan, and East Africa, skull fragments are lacking from the known record, and postcranial remains are all but unknown. The ramapithecines are now dated to 148 million years B.P. It has been suggested that
Ramapithecus
was a bipedal creature, and it is not unreasonable to assume that some form of erect feeding posture was used, both arboreally and terrestrially. More sophisticated use of the hands would be a consequence of such bipedal behavior. Conclusive interpretations of the appearance and significance of
Ramapithecus
await more complete fossil discoveries.
4.
Australopithecus robustus
(Paranthropus robustus—large ape akin to man)
One of the few supporters of Raymond Dart and his conclusions about the significance of the Taungs skull,
Australopithecus africanus
, was Dr. Robert Broom, a paleontologist who in 1936, at the age of 70, determined to locate an adult skull of an australopithecine. Broom felt that the limestone deposits of the Transvaal region of South Africa, some 200 miles northeast of Taungs, were possible sites of fossil manapes. He alerted the quarryman at Sterkfontein limeworks, G. W. Barlow, to the importance of looking for manlike remains. In July of that year, Barlow did present Broom with a braincast of a primitive hominid form, and an extensive search the following day turned up most of the rest of the skull, clearly similar to Dart’s find. Broom named the specimen
Australopithecus transvaalensis
, thinking that there were several basic structural differences meriting a separate species classification. This skull of a gracile australopithecine has since been reassigned to
Australopithecus africanus
. A number of other australopithecine finds were made at Sterkfontein during 1937 and 1938, making the original Taungs find a much more believable one.
In June, 1938 at a farm in Kromdraai, within two miles of Sterkfontein, Broom made another significant find. The newly discovered material, catalogued as TM1517, consisted of the skull, teeth, and some postcranial bones from a more robust, largerbodied type of australopithecine. As with the original Sterkfontein material, the initial discovery of these fossilized bones was made not by Broom but by a nonscientist. Quarry manager Barlow had brought Broom a primitive palate and molar tooth, which he had obtained from a local schoolboy, Gert Terblanche. Fresh break marks on toothed areas convinced Broom that additional portions of the skull were to be recovered. He went to the new location and traced the boy to his home, finally locating him at school. “I naturally went to the school, and found the boy with four of what are perhaps the most valuable teeth in the world in his trouser pocket.’’1 At the principal’s invitation, Broom delivered a lecture on bones and fossil digging to the teachers and students at the school, and upon school dismissal he and the boy visited the hillside at Kromdraai where the palate had been found. The boy delivered another sizable piece of the skull to Broom and through considerable searching and sifting they eventually located much of the rest of the skull. Broom bought the fossils from young Terblanche.
The new skull was given the name
Paranthropus robustus
,
reflecting his opinion that it was significantly different from
Australopithecus
as to merit a new generic classification. Originally considered to be much older than the Sterkfontein fossils, the Kromdraai skull is now regarded as being younger, approximately 2.5 to 2.0 million years old. There has been much disagreement as to how old the South African australopithecines are, owing to the absence of good datable material and to changing techniques for absolute dating. Relative dating, particularly fossil faunal comparisons with sites in East Africa, indicate that Sterkfontein is 3.0 to 2.5 million years old.
Five to six individuals were eventually found at Kromdraai. These South African hominids were larger than
Australopithecus africanus
. having a cranial capacity of 500 to 550 cc., as compared with 450 to 550 for the more gracile forms. The molars and premolars are larger, as compared with the incisor teeth, than in
africanus
. The robust skull is characterized by a prominent sagittal crest and cheek bones (zygomatic arches), skull specializations which were essential for the manipulation of the massive jaw. Diet may have been similar for the two forms, but it has been suggested that the robust form was a more efficient herbivore.
Robust skulls have been found at nearby Swartkrans, another mile or so from Kromdraai, most notably the wellpreserved SK 48 skull. SK 48 apparently belonged to a female. It has been dated to 2 1/2 to 2 million years ago, the same approximate age as Kromdraai. More recent estimates place Swartkrans at 1.8 to 0.8 million years before present. There is obviously considerable uncertainty as to the absolute ages of the South African sites, and any dates must be regarded as conjectural.
Beginning in 1959, East Africa has yielded remains of hyperrobust australopithecines. These forms will be considered later. All of the South African robust forms, though, have been placed in the classification
Australopithecus robustus
, following Broom’s species designation but not distinguishing the robust forms from the gracile generic designation. Pilbeam suggests that the larger body size and modifications in skull structure are explainable entirely within the context of the need for powerful muscles to operate the large jaws. Others have suggested that the gracile and robust forms are actually members of the same species, and that their differences in form reflect age and sexual differences, as well as geographical variation. It is not safe to assume at this time that all gracile forms are females and that all robust ones are males, however.
Australopithecus robustus
became extinct approximately 1 million years ago, having survived relatively unchanged for as long as 2 million years. Its somewhat younger age than
A. africanus
, as well as the morphological differences it expresses, suggest that the robust australopithecines are specialized offshoots in the australopithecine line.
5.
Australopithecus boisei
(Zinjanthropus boisei—the nutcracker man)
Some of the key fossil discoveries of this century have been more a result of fortuity than of hard work, as was the case with Dart’s and Broom’s initial discoveries. Dart more than made up for it with his fouryear effort to separate the lower jaw of Taungs from its rock matrix, as did Broom with his 15 years of digging and writing. For Louis and Mary Leakey, pioneer hominid excavators of East Africa, the discovery of the famous Zinjanthropus skull was a culmination of nearly 30 years of laborious work. Louis Leakey began the careful exploration of Olduvai Gorge in the Serengeti Plains of Tanganyika (now Tanzania) in 1931. Through the 1930s, 1940s, and 1950s he and his wife Mary, who has been regarded as the more meticulous member of the team, discovered the remains of numerous extinct animals, and more importantly, stone tools of early human cultures—hand axes, choppers, and cleavers. The maker of these tools eluded the Leakeys for years, until they seemingly discovered a representative skull of his in 1959.
One midJuly day in 1959, while Louis nursed a case of the flu back at the base camp, Mary set out to examine an area of the Gorge. She noticed on that day a portion of skull protruding from the rocky ground. Summoning a revitalized Louis, the two spent the next 19 days carefully removing a nearly complete skull of a newly recognized hominid. Zinjanthropus boisei, the nutcracker man, was named after the ancient name for East Africa as a whole, “Zinj,” and after Charles Boise, one of Leakey’s financial backers. Some of the many important discoveries that followed demonstrated that Zinjanthropus was probably not the toolmaker of Olduvai; but the discovery of this Olduvai hominid, well promoted by Leakey, was one of the exciting paleontological events of the century.
Zinjanthropus
lost its generic distinction when Phillip Tobias justified its reclassification as
Australopithecus boisei
in 1967. This hyperrobust australopithecine is characterized by a large sagittal crest and very prominent zygomatic arches. The canines and incisors are reduced in size, the chewing teeth are broad, and the forehead of Zinj is quite flat. The face is short and deep. It is the skull of a young male. Zinjanthropus has been accurately dated to 1.8 million years B.P. Unlike the sites of australopithecine hominids in South Africa, East African sites are very suitable for Potassium/Argon absolute dating. Olduvai provided a continuous geological and faunal history of 2 million years.
The cranial capacity of Leakey’s
Australopithecus boisei
is estimated as somewhat larger than those of most other known australopithecines, 530 cc. Significant postcranial differences have so far not been recognized. As with
A. robustus
, the buttressing of the
A. boisei
skull is a specialized response to the increased size of the jaws and cheek teeth. This bipedal hominid probably fed on tough vegetable matter, such as nuts and roots.
In 1968, Richard Leakey, one of the famous couple’s sons, and Meave Epps, who later became his wife, recovered a skull of
Australopithecus boisei
from the Koobi Fora region of Lake Turkana (formerly Lake Rudolph). The skull lacks teeth and the mandible, but is otherwise complete. Given the accession number KNMER 406 (previously FS158), the skull has a cranial capacity of less than 550 cc. The skull was originally dated at 2.6 million years B.P., but more recent analyses of the Koobi Fora sedimentary strata indicate that 2 million years ~ a more accurate estimate. As with the Zinj skull of Olduvai, this is a very robust skull.
6.
Homo habilis
(“able man” or “handy man”)
The discovery in Kenya of skull KNMER 1470 by Bernard Ngeneo, a member of Richard Leakey’s National Museum of Kenya expedition, is generally regarded as the find of this decade. Working in the Koobi Fora region of Lake Turkana (Lake Rudolph), Kenya, in 1972, Ngeneo noticed a number of bone fragments scattered over the surface of a slope. The pieces of bone were those of a hominid skull. Careful screening of 400 square meters of ground yielded several hundred fossilized fragments. As with many fossils recently exposed to the sun, wind, and rain, the brittle bones of 1470 had been damaged considerably. The process of fitting these pieces together into their proper orientations is best described as assembling a threedimensional jigsaw puzzle, when the puzzlesolver lacks some of the pieces. During the six weeks that followed recovery of the fragments, Meave Leakey, Alan Walker, and Bernard Wood were able to fit many of the pieces together, forming a very complete skull with a surprisingly large brain capacity, measured at 770775 cc. Tentative estimates of the age of Skull 1470 gave a range of 2.25 to 2.75 million years B.P. The younger age is presently favored.
This skull is characterized by a fairly high, steepsided cranial vault, slight brow ridge, and relatively thin cranial bones. The skull is now considered to be that of an early form of
Homo habilis
, the first hominid to be given the same generic designation as that of modern man. In this sense,
Homo habilis
can be regarded as the first true human.
Richard Leakey’s description of the 1470
Homo habilis
is not the first one for this species. Early
Homo
remains—mandibles, skull fragments, clavicles, tibiae
and fibulae, hand and foot bones— were discovered at Tanzania’s Olduvai Gorge beginning in 1960. The mandible found at Olduvai site F.L.K.N.N.I. was located by Richard’s brother Jonathan. It serves as the type mandible for
Homo habilis
, that newly recognized species of
Homo
first described in the April 4, 1964
Nature
article by the brothers’ father, L.S.B. Leakey. (The name
Homo habilis
, “able man” or “handy man,” was suggested to Leakey as an appropriate designation by Raymond Dart.) The Olduvai remains are given an age of 1.75 million years B.P.
Richard Leakey’s 1470 skull is a very significant find for two reasons. It gave further confirmation to Louis Leakey’s belief that early
Homo
lived contemporaneously with australopithecines, rather than being linearly descended and temporally separated from
Australopithecus,
Equally significant was the indication that the human ancestry can be traced back much earlier than had previously been believed. Skull 1470 added perhaps 500,000 years to the known age of
Homo
. (Subsequent discoveries at Olduvai, Lake Turkana, and elsewhere show that
Homo habilis
was fully adapted for upright walking and posture, and that he was a user of stone tools. Using a sample of 5 skulls found,
Homo
habilis had a cranial capacity of 600750 cc.)
7.
Australopithecus afarensis
(“Afar apeman”)
Generally speaking, paleontologists can be referred to either as
“splitters” or as “lumpers.” The splitters tend to favor the use of new generic and specific names for their discoveries, when unique morphology is evidenced. When L.S.B. Leakey introduced the names “Zinjanthropus”, “Kenyapithecus”, and
Homo habilis
, he was emphasizing the uniqueness of those fossil forms. In contrast, the “lumpers” prefer simplifying the nomenclature by grouping similar fossil finds into the same genus, sometimes even the same species. They suggest that individual, sexual, geographical, and temporal variations must be considered in describing an evolving lineage, and that separate species designations be used only for those forms that are significantly different morphologically. Simons and Pilbeam exemplified this approach to taxonomy in the 1960s when they reassigned previously described Sivapithecus, Bramapithecus, and Kenyapithecus fossils to
Ramapithecus
. Splitters and lumpers agree that names assigned to fossils are important in that they suggest phylogenetic relationships.
It was with considerable interest, then, that students of hominid evolution received word late in 1978 of the new species designation,
Australopithecus afarensis
. Extensive examination of 3.8 to 2.9 million-yearold hominid remains from Laetoli in northern Tanzania and from Hadar in the Afar region of Ethiopia convinced Don Johanson, Tim White, and Y. Coppens that a new species of australopithecine had been found. (Initial statements had suggested that these fossils would be assigned to
Homo
.) There is not universal agreement that the Afar apeman merits new species classification, But this should not be surprising in a period when frequent fossil discoveries are forcing continual reexamination of the evidence. Scientists do agree that these earliest of welldocumented hominid remains will prove to be of great importance to the understanding of hominid evolution.
The combined analysis of fossils from Hadar and from the Laetolil Beds (in Laetoli) is an example of the recent preference among anthropologists for basing generalizations on collections of remains rather than on individual finds. Fossils recovered from surface examination and sieving of the two sites represent nearly one million years of evolutionary history, and they are believed to be of common populations—a single hominid lineage. Johanson is codirector, along with M. Taieb, of the International Afar Research Expedition, and the Frenchman Coppens is a member of this team. White, an anthropologist currently with the University of Michigan, has done field work with Mary Leakey’s team at Laetoli. The Hadar fossil material has been collected since 1973, with the most important find, the remains of an adult female hominid, “Lucy,” being made in November, 1974. Work at Laetoli has continued since 1974, with much of the material important to the description of this species being recovered during the 1974 and 1975 seasons. (Mary Leakey continues to direct work at Olduvai Gorge, as well).
Discovery of “Lucy” ranks as one of the great achievements in paleontological history, and her naming must rank with the classic examples of scientific humor. Early examination of the skeletal fragments of this three millionyearold hominid took place during a playing of the taped Beatles song, “Lucy in the Sky with Diamonds.” The name stuck. The “Lucy” skeleton is 40% complete. Cranial remains are limited, but a good mandible was found. The postcranial skeleton, usually poorly represented in the fossil record, is of primary importance. It indicates that this 3.5 to 4.0 foot tall hominid was welladapted for bipedal locomotion. Fossil hand bones from a nearby Hadar locality bear strong resemblance to the modern human hand, in their apparent manipulative ability. “Lucy”, who received the catalog designation A.F. (Afar Locality) 2881, is estimated to have been in her twenties when she died. PotassiumArgon dating techniques suggest that she and the dozen or so other individuals whose remains were recovered at Hadar lived 3.3 to 2.6 million years B.P. Five to seven of the hominids found in association with each other may have comprised a family unit.
Hominid remains from the Laetolil Beds are somewhat earlier than those from Hadar, being 3.83.6 million years old. The mandible L.H. (Laetoli Hominid) 4 is the type mandible for the species
Australopithecus afarensis
. This mandible, as with the others recovered at both sites, is relatively light, with a Vshaped dental arcade. The appearance of the jaw, as well as the robustness of the postcranial skeleton are examples of the retention of apelike characteristics in
Australopithecus afarensis
.
A high Level of sexual dimorphism characterizes these fossils. This interpretation is preferred to the possibility that these are not male and female variances, but rather two different species of Hominids.
Australopithecus afarensis
has been proposed as that form which subsequently diverged into australopithecine and human lineages. The discovery at Laetoli, East Africa of 316 millionyearold fossil footprints by members of Mary Leakey’s fossil hunting team confirms very early erect walking. The footprints, left by Afar apemen, indicate that the pelvic girdle, the leg bones, and the angle of the foremen magnum for this hominid were essentially those of modern man. Increase in brain size,
however, is a relatively recent development, which experienced acceleration approximately one million years ago.
In discussing some of the more salient aspects of current evolutionary thought, an effort has been made to avoid considering earlier forms of hominids as incomplete or imperfect humans. It is a mistake to regard earlier forms only in relation to modern man, or to suggest that the evolutionary process of the past 15 million years has been one of direction toward producing today’s man. Earlier hominids had their own unique qualities, and these species enjoyed long periods of successful existence.
Homo sapiens
is a species that has been present on earth for approximately 200,000 years, as compared with 1 million years for Homo erectus or for
Australopithecus robustus
.
Another aspect of our uniqueness is that we happen to be the sole surviving representatives of a family that was formerly diverse. Our longrange success as a species and the evolutionary trends that we continue to express are matters which remain to be seen.