Evolution: Humans: Origins of Humankind

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Origins of Humankind

The Hominid Family Tree

Orrorin tugenensis
(6 mya)

Ardipithecus ramidus
(4.4 mya)

Australopithecus anamensis
(4.2 to 3.9 mya)

Australopithecus afarensis
(3.6 to 2.9 mya)

Kenyanthropus platyops
(3.5 to 3.3 mya)

Australopithecus africanus
(3 to 2 mya)

Australopithecus aethiopicus
(2.7 to 2.3 mya)

Australopithecus garhi
(2.5 mya)

Australopithecus boisei
(2.3 to 1.4 mya)

Homo habilis
(2.3 to 1.6 mya)

Homo erectus
(1.8 to 0.3 mya)

Australopithecus robustus
(1.8 to 1.5 mya)

Homo heidelbergensis
(600 to 100 tya)

Homo neanderthalensis
(250 to 30 tya)

Homo sapiens
(100 tya to present)

mya = millions of years ago tya = thousands of years ago

Australopithecus afarensis (3.6 to 2.9 million years ago)

Species Description:

Australopithecus afarensis had a very low forehead, a face that projected far forward (as viewed in profile), and a very prominent brow ridge. A. afarensis is the earliest species for which we have reliable brain and body size estimates, thanks to a rich fossil record for the species.

The brain of A. afarensis was about one-third the size of the average modern human brain, or about the same size as a modern ape's brain. Males and females varied significantly in body size, with males standing approximately 4 feet 11 inches tall and weighing 100 pounds and females standing about 3 feet 5 inches tall and weighing about 62 pounds. Males also typically had large crests on top of their skulls; females did not.

The knee and pelvic bone structure of A. afarensis were very humanlike, leaving no doubt that A. afarensis walked upright. A. afarensis probably inhabited the savannas and open woodlands where they likely found fruits, seeds, and roots.

	Fossil Finds:

		Laetoli footprints Estimated age: 3.6 million years Date of discovery: 1978 Location: Laetoli, Tanzania These fossilized footprints reveal important information about the two individuals who made them. First, it's clear that they walked upright. Also, from stride length, scientists estimate that they were about 4 feet 8 inches and 4 feet tall, respectively. (The footprints are linked to A. afarensis by the fossil jawbones of the same species found nearby.)

		AL 129-1 Estimated age: 3.4 million years Date of discovery: 1973 Location: Hadar, Ethiopia This intact A. afarensis knee joint looks very much like a small version of an anatomically modern human knee and likely worked similarly. The angle of the joint all but confirms A. afarensis's ability to walk upright.

	Lucy Estimated age: 3.2 million years Date of discovery: 1974 Location: Hadar, Ethiopia Analyses show that Lucy was approximately 3 feet 6 inches tall, weighed 62 pounds, and was 25 years old when she died. This is the most complete A. afarensis skeleton yet described.

-> Go to Kenyanthropus platyops



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