Hominid Evolution

Topics: Human evolution, Human, Australopithecus Pages: 14 (2424 words) Published: February 21, 2011
Hominid Evolution

The evolution of hominids has been and still is a heated topic of debate. Many scientists

debate over which species can be classified as “human”. The root "hominid" refers to members

of the family of humans, Hominidae, which consists of all species on our side of the last

common ancestor of humans and living apes. The time split between humans and living apes

used to be thought of fifteen to twenty millions of years ago, but now the time period has shifted

to around five million years ago.

Ardipithecus ramidus is said to have live around 4.4 million years ago. The original

fossils from this species were placed with the Australopithecus genus; however, a new genus was

designated to this group by Tim White. Tim White is an anthropologist and co-author of

Geological Study of America Bulletin in which this distinction was first stated. This hominid is

different from its predecessors because it lacks an incisor tooth, yet posses an ape-like molar

structure. Another major defining characteristic of A. ramidus is that the cranial bones that have

been discovered reveal this hominid walked on four appendages rather that the more developed

species which walked on two.

The next hominid in line is Australopithecus anamensis. This hominid lived for the

period of 3.5-4.17 million years ago. It was discovered by a Harvard Expedition to the East Lake

Turkana in 1995. The classification of A. anamensis was done after extensive research by Meave

Leakey and associates. The skeletal structure of this hominid reveals that it was bipedal

(walking on two legs) which distinguishes it distinctly from A. ramidus. However, A. anamensis

possessed some traits that were similar to hominids before it such as a dental structure that is

similar to that of an ape and an ape-like skull. On the other hand, this hominid has an unique

thick tooth enamel and expanded molars.

Between 3.9 and 3.0 million years ago, Australopithecus afarensis roamed the earth. It

was first discovered by Donald Johanson and Tim White in 1978 but the validity of this

discovery was questioned for many years. The most popular member of this species would be

“Lucy” who was discovered in Hadar, Ethiopia in 1974. The skull of this A. afarensis is like that

of a chimpanzee, but it has human-like teeth. It’s canine teeth are larger than modern day apes

but more pointed than humans. Anthropologist Louis Leakey distinguished that the pelvis and

legs of A. afarensis show that the hominid walked on two legs and was significantly strong for its

small size (ranging from 3’6” to 5’0”). Some anthropologists even believe that the structure of

this hominid suggests it was adapted for climbing trees because of its strong structure and curved

bones in the fingers and toes. Australopithecus afarensis was one of the first hominids

discovered to begin to resemble modern day men.

The species Australopithecus africanus was first name in Nature magazine by Raymond

Dart in 1925. He names the species because of his findings of the Taung Child Skull. However,

many paleontologists of the time rejected this classification and said that the skull was one of an

early gorilla or chimpanzee. Because of the great debate over the species, Dart never went back

to Taung for further research. Other excavations have found remains of A. africanus in

Sterkfontein, Makapansgat, and Gladysvale. These remains date back anywhere from 2.9 to 2

million years ago. This species was declared bipedal because of its 5 lumbar vertebrae where

most humans have 6 and chimps have 4. The post canine teeth in A. africanus are much broader

and all of the teeth in this species have a great enamel thickness along the tooth wall which set

them apart from predeceasing species. Their brain capacity is said to be anywhere from 428 cc to

625 cc, and they...
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