Homo Habilis and Associates
Posted: Thursday, July 05, 2007
by Jerry Boone
http://merechristianity.us/
Dryopithecines - Lived 15 to 20 million years ago in Europe, Asia, and Africa.
Mary Leakey found and named "Proconsul africanus" in 1948. They are thought to be forest dwellers. Their teeth are ape-like -small, with canines sharp and projecting. Probably dryopithecines walked in a fashion similar to monkeys on the top of branches. Manny different species have been discovered. It's impossible to tell how they were related.
Ramapithecines - Lived 8 to 14 million years ago in Africa, Asia, and Europe.
Teeth and jaw fragments were the only fossils known until 1977 when a complete skull was located. Richard Leakey divides the fossils into three groups: Ramapithecus - the smallest group, individuals probably weighed 45 pounds. Sivapithecus - similar to ramapithecus but larger. Gigantopithecus - as the name implies, they were much larger.
Fragments of a Ramapithecus jaw bone were reconstructed, and it was thought to have a parabolic (curve-shaped) dental pattern. That plus the relative size of its canine and other teeth led the experts to believe Ramapithecus might be an ancestor of humans.
During the 1970's, several paleontologists took another look at the reconstructed jaw. Something seemed out of place. They rearranged it, and the tooth row came out much the same as those of other Miocene apes, not curved as in humans. Later discoveries proved the square ape jaw alignment correct. Authorities concluded Ramapithecus was more closely related to the orangutan than to man.
Australopithecus afarensis - Lived between 3 to 4 million years ago in north, south, and east Africa. Height: 3.5 to 4 feet; Weight: 55 to 120 pounds; Head: Described variously as the size and shape of a small female gorilla or like that of a chimpanzee; Brain: 500 cubic centimeters, comparable to either chimpanzee or gorilla, about one-third the size of modern human.
In 1974, Donald Johanson found a 40 percent complete skeleton of a 3.2 million year old afarensis which he named Lucy after the Beetles' hit "Lucy in the Sky with Diamonds." Johanson first classified her in the genus Homo. By 1979, he decided the fossil was too "primitive" and required a classification of her own.
Johanson said that from the neck up Lucy was a chimpanzee, but from the waist down, human. Since then, however, details have surfaced about Lucy's anatomy which show her features are quite a bit different from human's.
Her wide sacrum and shallow pelvis allowed only a small birth canal which would restrict her newborn infant's brain to no larger than a chimpanzee's infant brain. Lucy's hands and feet were missing. Fortunately, bones from other afarensis have by and large filled in the gaps.
They reveal long curved fingers and toes, not as long as modern apes, but longer than human's. Likewise, Lucy's upper arms were 84 percent as long as her thigh bone. The human ratio is 72; chimpanzees, 110; and the most acrobatic ape of all - the gibbon has a ratio of 130. Long fingers and toes plus long arms and short legs all suggest afarensis was more at home in the trees than modern humans, but less attached to trees than either chimpanzees or gibbons.
What really makes afarensis interesting to paleontologists is Johanson's claim that Lucy was bipedal. He thinks that this small ape type of creature walked about very much like you and me.
Whether Lucy walked upright in the manner of Homo sapiens is still a matter of controversy in the academic community. Johanson claims that the shape of afarensis' foot and heel shows that it spends most of its time on the ground. And the heel was large enough that afarensis could support its weight on its feet. Lucy would not need to lean forward like a chimpanzee and place most of her weight on her knuckles.
The second reason for believing Lucy walked erectly was a small bone discovered twenty-six feet below the skeleton. Johanson assumes it is part of Lucy. The bone is the top portion of a femur with two bony bumps, or condyles, on the end. He says they look very much like the condyles on a human. Chimpanzee condyles are shorter and rounder. Moreover, the hip joint and the thighbone form a downward and inward slant which is a distinctive feature of a two-legged walker.
Unfortunately, the right half of Lucy's pelvis was missing. The left was bent out of shape and shattered into forty pieces. Anthropologist Owin Lovejoy pieced it back together and made laboratory 'corrections" on the distorted pelvis. When reconstructed, it became wider and more bowl shaped like a human pelvis. Johanson claimed this as further evidence of Lucy's bipedalism.
Experts on the other side accept Johanson's view that afarensis walked on two legs. They just say Lucy probably walked in a bent-hip, bent-kneed fashion of a bipedal chimpanzee. Lucy and her fellow afarensis are adapted for trees say these skeptics.
Support for their position came in 1990 when the top of an afarensis upper arm was discovered. The pronounced ridges on the bone left little doubt that these creatures had good upper body strength. That plus their long toes, fingers, and arms meant they were well equipped for life in the trees.
Part of their reason for thinking Lucy a rather clumsy biped comes from measurements taken from a cast of Lucy's unrestored pelvis. Archaeologists from Stony Brook (State University New York) viewed the evidence before Lovejoy's rearrangement of the pelvis. Evidently, Lovejoy could not convince them with his reconstruction. The debate continues.
Does it really matter if she did walk upright? Biologist Michael Pitman says that the mountain gorilla from Zaire has feet that resemble those of humans. "Its arms are not too long nor its legs too short - a young gorilla can rear up and walk in a human way resting on the sole on its foot rather than the side." And they spend about 80 percent of their time on the ground. But no one claims the Zaire gorilla is human.
Other Characteristics
Afarensis show dramatic differences in overall body size. Johanson interprets this as just the difference between male and female. Richard Leakey thinks there's more to it than that. Some afarensis weigh 55 pounds, others weigh in at 120. Leakey concludes that the weight difference is too great to be explained by sexual differences. He says we are probably looking at two separate species.
Australopithecus afarensis lived for almost a million years remaining remarkably similar for the entire period. It's brain never evolved in size. It never became more human.
No tools have ever been associated with afarensis or any of the other australopithecines.
What can we say of Australopithecus afarensis? Was it an ape, apeman, or an extinct side line from a common ancestor? Johnson says it was a primitive species of australopithecines and probably ancestral to all the other australopithecines and Homo as well.
Mary and Louis Leakey think no australopithecine belong on the human line. Richard Leakey seems to regard afarensis as a questionable ancestor of man. As you can see, paleontologists can not agree on where to place Australopithecus afarensis among men and apes.
Two prime mysteries revolve around afarensis. First, where did they come from? A significant 400,000 year gap separates afarensis from Australopithecus ramidus with no hominid fossils in between.
Second, did afarensis evolve into Homo? Anatomically, afarensis is the closest fit. Besides, there are really no other candidates around. Yet we find another very inconvenient million year gap between afarensis and any type of Homo. Again, there are no hominid fossils in between. Paleontologists, for their part, have not been sitting about idling away their time. They eagerly search for something, anything, to fill those gaps. But despite their efforts, the fossil record remains a record, not of evolution, but of gaps.
Homo Habilis - Lived between 1.5 and 2 million years ago in east Africa. Nicknamed the "Handy Man."
Height: 3.5 to 4 feet; Weight: rough estimate of 95 pounds. Fossils: Skull fragments, part of a jaw, teeth, and and foot bones form four individuals were found at Olduvai Gorge from 1960 to 1986. Additional skulls were found at Koobi Fora in northern Kenya.
Appearance: Johanson says that based on skeleton fragments found at Olduvai Gorge, habilis was built like an australopithecus in overall body size and proportions. Brain Capacity: 650 cubic centimeters compared to 380 - 530 c.c. for australopithecus, and 1400 c.c. for modern humans.
A genus is usually defined as a group of species more closely related to each other than to any other species. Homo is loosely described as a "bipedal primate with a big brain."
One controversy after another has clouded Homo habilis from the beginning. From what we can tell of their few scattered bits of fossils, habilis probably looked like an australopithecus, which in turn resembled a small gorilla. Australopithecines supposably walked erect, so why is habilis classified as a Homo rather than an australopithecine?
Habilis acquired the Homo designation primarily because of its somewhat larger brain. The distinction is arbitrary. Yes, habilis' 650 Cubic centimeter brain capacity is larger than the 380 to 530 c.c. of an australopithecine, but no where near the 1400 c.c. human brain. Critics say habilis is nothing more than an australopithecine with a slightly larger brain.
Then there is the sticky problem of tool use. Flakes of stone, rough edged cobbles, and broken animal bones - tools, or at least they are interpreted as such, were discovered about the same distance between a Homo habilis and an Australopithecus boisei skull. Paleontologists credit habilis with the tools.
All in all, naming this species "handy man" assumes a great deal more than we really know. Did these stones and bones belong to boisei or habilis? Were these instruments modified for use, or were they simply used as found? Or did anyone use them at all?
Does it really matter? In his book Ancestors, Johanson tells us that chimpanzees in the forests of Tai National Park in the Ivory Coast have been observed carrying sticks through the jungle to break open panda nuts. And the chimps use stones as hammers to crack the nutshells. They even save a good stone for future use.
Also chimpanzees are capable of learning how to chip stone flakes for obtaining food. Granted, the chimp-cracked stones are not of the caliber of those associated with habilis. Still the fact remains, chimpanzees make and use tools; yet no one classifies chimps in the genus Homo.
About six miles away from the boisei and habilis fossils, researchers uncovered a circle of loosely packed stones, which is thought to be a wind breaker such as a hunter might make. Again, the assumption is that habilis did it. Maybe, maybe not. But it is hard to build a convincing case that habilis was a toolmaker based upon flaked stones at one location and a crude circle of rocks at another.
Other habilis critics, a growing body of scholars says Johanson, argue that the fossils lumped together as habilis show too much variation to belong to the same species. Sound familiar? That's the same dispute paleontologists had over Australopithecus afarensis.
Who was Homo habilis? Same or similar to Australopithecus, or a breed apart? Tool user, toolmaker, or both? One species? Two? Three or more? There is very little we can say for certain. We find a creature with a brain a little larger than australopithecines but much smaller than human. He may have used tools of a better quality than chimpanzees can produce today. It is possible, although this is pure speculation, that habilis is the one responsible for putting those stones in a circle too.
Some paleontologists believe that Australopithecus afarensis somehow evolved into habilis. However, nearly a million years lie between the two species with nothing to fill the gap. Consequently, habilis' ancestors remain an unsolved mystery without even a decent clue.
Questions to Consider:
1.Does the fossil record clearly show the evolution of mankind, or is it a series of gaps filled with speculation based on meager evidence?
2. Why do you think paleontologists disagree among themselves about the ancestors of humans?
Jerry Boone, Gatlinburg, Tennessee, United States webmaster@merechristianity.us Mr. Boone is a sailor, author, and webmaster of http://merechristianity.us with a Bachelor of Arts degree in Anthropology from Georgia State University. His works include: Mere Christianity.us and SAFETY LINE - EVIDENCE OF THINGS NOT SEEN, an apologetic study published 1998.
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Top-level comments on this article: (1 total)this article helped me a Lot thanks!
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