human evolution part ii

Human EvolutionPart 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 3.2 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 – (2.3- 3 million) was thought to descend from A. afarensis. It was taller and heavier, with a slightly larger cranial capacity.

A. 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, paleoanthropologistsworking in East Africa found a hominid skullwith 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 theirgrouping under the genus “Homo” Homo habilis (“handy human” -tool-maker) descended from A. afarensis (2.5 – 1.5 millionyears).

Tool marks on animal bones found near

H. habilus fossils suggest that they ate

meat.

H. Erectus (“upright human”) descendedfrom H. habilis. Apparently the first humanto travel out of Africa. They were originallyfound 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, andlarge, protrudingteeth. The brainwas 2/3rds of modern humans.

H. Erectus skeleton: (12 yr old boy)If he had grown to adulthood,he would have been around6 feet tall.

“Charles Darwin predicted that human ancestors would be found in Africa.”

In the 1960s Louis and Mary Leakeydiscovered fossils in East Africa’sOlduvai gorge (Tanzania), that datedas far back as 2 million years.(They had been working there formany 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 theNeanderthalsand eventuallyled to thedevelopmentof modern humans.