Human Evolution Part II

Ardi – Our very early ancestor The fossil skeleton of a species, discovered in Ethipoia in 1994, called Ardipithecus ramidus dated to 4.4 million years. It belonged to a small-brained, 110 pound female nicknamed “Ardi.”

Discoverers proposed that she was a new kind of hominid, the family that includes humans and our ancestors but not the ancestors of other living apes. They say that Ardi's unusual anatomy was unlike that of living apes or later hominids, such as Lucy. Instead, Ardi reveals the ancient anatomical changes that laid the foundation for upright walking. Not all paleoanthropologists are convinced that Ar. RAMIDUS was our ancestor or even a hominid. But no one disputes the importance of the new evidence. (Science 12/2009)

A thorough analysis of a large number of collected specimens shows it is an interesting mosaic of traits: it was bipedal, but not quite so well adapted to terrestrial locomotion as we are, and it had feet with an opposable big toe. And of course it had a small brain, only a little larger than a chimpanzee's. (P.Z. Meyers U of Minnesota)

But Ardi's feet, pelvis, legs, and hands suggest she was a biped on the ground but a quadruped when moving about in the trees. Her big toe, for instance, splays out from her foot like an ape's, the better to grasp tree limbs. Unlike a chimpanzee foot, however, Ardipithecus's contains a special small bone inside a tendon, passed down from more primitive ancestors, that keeps the divergent toe more rigid. Combined with modifications to the other toes, the bone would have helped Ardi walk bipedally on the ground, though less efficiently than later hominids like Lucy. The bone was lost in the lineages of chimps and gorillas. (National Geographic News 3/1/10)

1974 – Donald Johanson finds a 3 1974 – Donald Johanson finds a 3.2 million year old fossil of a primate in the Afar Valley region of eastern Africa. (also Ethiopia)

The cranial capacity is about 1/3 of a modern human, and about equal to that of a chimp. Its height was also equal to a chimp. The pelvis and leg bones, however, indicate that The organism was an upright-walking hominid. (Hominids are the group that comprises humans and their intermediate ancestors.) It and other specimens of the same species date about 3-3.9 million years ago. It was unofficially called “LUCY”

Lucy’s Scientific Name = Australopithecus afarensis Lucy stood only a little over a meter.

“The Week” February, 2011

Australopithecus africanus – (2 Australopithecus africanus – (2.3- 3 million) was thought to descend from A. afarensis. It was taller and heavier, with a slightly larger cranial capacity.

robustus and A. boisei date 1 – 2.6 million years. They had heavier skulls and larger teeth. Their general appearance suggests that they probably descended from Lucy’s species.

Working in the 1960s, paleoanthropologists working in East Africa found a hominid skull with a much larger brain case than the australopithecines. They had larger cranial capacity and were often found with tools. Their human like morphology resulted in their grouping under the genus “Homo” Homo habilis (“handy human” -tool-maker) descended from A. afarensis (2.5 – 1.5 million years).

Tool marks on animal bones found near H. habilus fossils suggest that they ate meat.

H. Erectus (“upright human”) descended from H. habilis. Apparently the first human to travel out of Africa. They were originally found in the Pacific Island of Java, and have been found in China, Europe, and Africa. H. erectus had a thick skull, large brow ridges, a low forehead, and large, protruding teeth. The brain was 2/3rds of modern humans.

H. Erectus skeleton: (12 yr old boy) If he had grown to adulthood, he would have been around 6 feet tall.

“Charles Darwin predicted that human ancestors would be found in Africa.” In the 1960s Louis and Mary Leakey discovered fossils in East Africa’s Olduvai gorge (Tanzania), that dated as far back as 2 million years. (They had been working there for many years prior to the 1960s)

They had discovered A.boisei in 1959,and later, H. habilus. Their son, Richard Leakey and his wife, excavated the earliest fossils of H. erectus in 1984.

H. sapiens descended from H. Erectus. (H. sapiens consisted of “early,” and the “modern.” The Cro Magnons were an early’ form of modern humans. They had a cranial capacity equal to modern humans.) It is believed that Neanderthals came about at some time during the existence of early Homo sapiens, but that became extinct.)

Cro Magnon man outlived the Neanderthals and eventually led to the development of modern humans.