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The Earliest Hominine's The first undoubted homicide discovered thus far is Ardipithecus radius, which was found in 1994 and is known from 17 fragments of teeth and bone. It dates to approximately 4. 4 million years ago. Thought to be the descendent genus of Ardipithecus is the genus Australopithecus; individuals of this genus were bipeds while on the ground and had ape-like brains and dexterous hands. There are at least six species of Australopithecus: A. anamnesis, A. afarensis, A.
aethiopicus, A. africanus, A. boise, and A. robust. In 1924 an unusual fossil was brought to Raymond Dart, an anatomist at the University of Witwatersrand in Johannesburg.
This fossil had a curious mix of ape-like and human-like traits. Dart named the fossil Australopithecus africanus and claimed that, based on the forward position of the foramen magnum, the creature was a biped. At least four species are recognized: A. afarensis and A. africanus being smaller and lacking the massive jaws of the two larger species, A.
boise and A. robust. A. afarensis and A. boise are from East Africa, while A. africanus and A.
robust are from South Africa. An earlier species, A. anamnesis comes from Kenya, while a single representative of a sixth species, A. aethiopicus comes from West Turkana and is known as the black skull for its distinctive black staining. Australopithecus africanus has been discovered at three South African sites: Thing, Makapansgat, and Sterkfontein. All of these sites range in date from 3 to 2. 3 mya; however, a partial foot may be as old as 3. 5 million years.
Australopithecus afarensis dates to between 3. 9 and 2. 9 mya, and was discovered in the 1970 s and 1990 s in the Afar region of northern Ethiopia. Included in this species are the two famous finds of Don Johanson: the remarkably complete female skeleton AL 288 - 1, known as Lucy, and the collection of 13 individuals at Afar Locality 333 which has come to be known as the First Family. Material nearly 4 million years old from Laetoli in Tanzania has also been ascribed to A. afarensis, despite suggestions that the wide variation in size of individuals may mean the presence of 2 species. It is likely, however, that A. afarensis size differences represent sexual dimorphism similar to Miocene apes and intermediate between the greatly dimorphic modern gorillas and the less dimorphic chimpanzees.
Other East African sites have yielded fossils similar to A. afarensis or A. africanus. These sites are all 2 million or more years old. The individuals ranged between 3. 5 and 5 feet, with weights of between 29 and 45 kg. Australopithecus afarensis and A.
africanus are considered to be gracile or smaller australopithecine's. These two species possessed small incisors, short canines in line with the other teeth, and a rounded dental arch. No gap between the canines and incisors in the upper jaw (diastema), as seen in apes, was present. The molars and premolars were larger than those of modern humans, but were similar in form. Tooth wear indicates that these species chewed as humans do, but with 2 to 4 times the force.
The diet was largely tough, fibrous vegetation. A. afarensis individuals tend to show more sivapithecine features, such as a less-rounded dental arch, less shearing tooth wear, slight diastema, and some canine projection, than the later A. africanus individuals. These sivapithecine features suggest a Miocene sivapithecine-like ancestor. Some sex differences have been noticed in these two australopithecine's: males seem to develop a bicuspid first lower premolar while females do not; and females seem to possess skeletal features better suited to tree-climbing than males.
These differences suggest that males and females may have had slightly different foraging strategies, with males spending more time on the ground and females exploiting trees. Cranial capacity of A. afarensis was 310 to 500 cc and that of A. africanus was 428 to 510 cc (roughly the size of a chimpanzee and 1 / 3 that of a human); intelligence, however, is more a factor of the ratio of brain to body size. Unfortunately, the vast rang of body sizes in these forms makes this ratio difficult to assess. It is believed that these two australopithcines had mental capabilities equivalent to those of the great apes of today.
What is significant is the fact that at 4 million years ago, there existed a bipedal homicide. Evidence supporting this fact includes: forward placement of the foramen magnum indicating a head balanced atop the spinal column; human-like curvature of the spine; forearms shorter than those of an ape indications of a lower centre of gravity than apes; the Laetoli footprints; and hip and knee anatomy. On the other hand, these australopithecine's still retained a slightly divergent great toe and shoulder girdle well suited for climbing. Bipedal locomotion preceded any increase in brain size; in fact, australopithecine's lacked the prolonged maturation of modern humans and likely matured as apes do. Upright walking set the stage for larger brain sizes but was not the sole cause of these later increases. Robert Broom and John Robinson first discovered Australopithecus robust, a larger, more robust australopithecine, in 1948 at the sites of Swartkrans and Kromdraai (South Africa).
While no accurate dates are available, it is believed that the deposits are 1. 8 to 1 million years old. A. robust is similar to A. africanus, except for thicker bones relative to size, with large muscle-markings that included an ape-like sagittal crest on the large skull.
Cranial capacity of A. robust was around 530 cc and the crest served to anchor the massive chewing muscles of powerful jaws. Such chewing apparatus is also seen in the modern gorilla and is an example of convergent evolution in these two species. In East Africa, a robust australopithecine species also exists: Australopithecus boise. First found at Ngorongoro Crater of Olduvai Gorge in 1959 by Mary Leakey, the original specimen was named Zinjanthropus by Louis Leakey. Further study revealed it was another australopithecine and it was renamed A.
boise. Potassium-argon dating places the find at 1. 75 million years old; however, another specimen thought to be an earlier A. boise is dated to 2. 5 mya. The most recent A. boise fossils are only 1. 3 million years old. A.
boise is similar to A. robust in form; however, the East African robust australopithecine is even more robust than its South African relative. A. boise s cranial capacity was 500 to 530 cc and its weight was 34 to 49 kg, compared with the 32 to 40 kg range of A. robust. The Black Skull from Kenya shares some primitive features with Australopithecus afarensis and, being far earlier than the other A.
boise finds, has been suggested as being descended from A. afarensis. While your text considers this specimen to be an early A. boise, other researchers prefer to place the Black Skull in a separate species, Australopithecus aethiopicus. It is uncertain whether A. robust represents a southern offshoot of the A.
boise lineage or an example of convergent evolution that evolved from A. africanus. A. boise and A.
robust were both highly efficient chewing machines which had a diet of tough, uncooked vegetation. The law of competitive exclusion states that when two closely related species compete for the same niche, one will out compete the other, bringing about the loser s extinction. The specialized vegetarian robust australopithecine's avoided such competition with early Homo and these two genera were thereby able to coexist for some 1. 5 million years. Older than Australopithecus afarensis is Australopithecus anamnesis.
This species is a recent find, dated to 4. 2 to 3. 9 mya, and is represented by an arm bone found in 1965 and two jaws and a tibia found in 1995. The jaws were ape-like with a shallow palate and large canines, but the tibia was similar to that of A. afarensis and is the oldest direct evidence of bipedalism yet found. Older still than Australopithecus anamnesis is Ardipithecus radius, a species known from pieces of 17 individuals from Ethiopia dated to 4. 4 mya. No pelvic, foot, or leg bones are among the fossils; however, the shapes of the canines and vertebral elements are homicide in appearance. It is believed that the Australopithecus evolved, by way of Ardipithecus, from some Miocene sivapithecine ancestor.
Evolution of the hominine's was not steady; it was far more likely periods of stasis punctuated by short episodes of rapid changes, as evidenced by long periods of little change between the diversification of the various Australopithecus species. At the close of the Miocene, the climates changed, with the Mediterranean Sea drying up temporarily and the vast forests undergoing a reduction in size. More open country was available, requiring the ancestors of the hominine's, as well as the early hominine's themselves, to spend more time on the ground. New foods were made available as older arboreal ones disappeared; dentition therefore was altered. With the reduction of canines came, it is believed, a reliance on hands for defense, using clubs or rocks. This use of objects for defense may have set the stage for tool-use / tool -manufacture.
There is no evidence of tool use or manufacture among australopithecine's, but modern chimps and orangs can and do make tools; in fact, under experimental conditions, chimps have been able to make crude chipped stone tools. Based on the abilities of modern chimps and orangs, it is believed that the australopithecine's used natural objects as tools. There is a 2 million-year gap between the last sivapithecine and the first australopithecine; the individuals in this gap likely were undergoing the transition to bipedalism. Bipedalism has drawbacks: exposure of soft belly to attack; slower running and poorer ability to change direction instantly; back problems, hernias, circulatory problems associated with the upright posture; and the consequences of serious leg injury. So why bipedalism? Perhaps for: carrying foraged foods from place to place carrying infants so that fatal falls from mother were minimized; faster food gathering and longer treks with less fatigue; spotting food sources or predators from a distance with the increased height and visual perspective of standing on the hind limbs; or freeing hands to fend off predators by using natural objects as weapons.
In any case, the bipedal adaptation was likely the result of several factors.
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