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The evolutionary tree shows the relationship between humans and the great apes. All great apes, including baboons, gibbons, orangutans, gorillas, chimpanzees, humans, and human ancestors, belong in the superfamily Hominoidea. Of these great apes, all but baboons and gibbons belong in the family Hominidae. Gorillas, chimpanzees, humans, and human ancestors belong in the subfamily Homininae. Humans and their direct ancestors belong in the tribe Hominini.
This chart shows the evolution of modern humans.

Very early hominins

Three species of very early hominids have made news in the past few years. The oldest of these, Sahelanthropus tchadensis , has been dated to nearly 7 million years ago. There is a single specimen of this genus, a skull that was a surface find in Chad. The fossil, informally called “Toumai,” is a mosaic of primitive and evolved characteristics, and it is unclear how this fossil fits with the picture given by molecular data, namely that the line leading to modern humans and modern chimpanzees apparently bifurcated about 6 million years ago. It is not thought at this time that this species was an ancestor of modern humans.

A second, younger species, Orrorin tugenensis , is also a relatively recent discovery, found in 2000. There are several specimens of Orrorin . It is not known whether Orrorin was a human ancestor, but this possibility has not been ruled out. Some features of Orrorin are more similar to those of modern humans than are the australopiths, although Orrorin is much older.

A third genus, Ardipithecus , was discovered in the 1990s, and the scientists who discovered the first fossil found that some other scientists did not believe the organism to be a biped (thus, it would not be considered a hominid). In the intervening years, several more specimens of Ardipithecus , classified as two different species, demonstrated that the organism was bipedal. Again, the status of this genus as a human ancestor is uncertain.

Early hominins: genus Australopithecus

Australopithecus    (“southern ape”) is a genus of hominin that evolved in eastern Africa approximately 4 million years ago and went extinct about 2 million years ago. This genus is of particular interest to us as it is thought that our genus, genus Homo , evolved from Australopithecus about 2 million years ago (after likely passing through some transitional states). Australopithecus had a number of characteristics that were more similar to the great apes than to modern humans. For example, sexual dimorphism was more exaggerated than in modern humans. Males were up to 50 percent larger than females, a ratio that is similar to that seen in modern gorillas and orangutans. In contrast, modern human males are approximately 15 to 20 percent larger than females. The brain size of Australopithecus relative to its body mass was also smaller than modern humans and more similar to that seen in the great apes. A key feature that Australopithecus had in common with modern humans was bipedalism, although it is likely that Australopithecus also spent time in trees. Hominin footprints, similar to those of modern humans, were found in Laetoli, Tanzania and dated to 3.6 million years ago. They showed that hominins at the time of Australopithecus were walking upright.

There were a number of Australopithecus species, which are often referred to as australopiths . Australopithecus anamensis lived about 4.2 million years ago. More is known about another early species, Australopithecus afarensis , which lived between 3.9 and 2.9 million years ago. This species demonstrates a trend in human evolution: the reduction of the dentition and jaw in size. A . afarensis ( [link] ) had smaller canines and molars compared to apes, but these were larger than those of modern humans. Its brain size was 380–450 cubic centimeters, approximately the size of a modern chimpanzee brain. It also had prognathic jaws , which is a relatively longer jaw than that of modern humans. In the mid-1970s, the fossil of an adult female A . afarensis was found in the Afar region of Ethiopia and dated to 3.24 million years ago ( [link] ). The fossil, which is informally called “Lucy,” is significant because it was the most complete australopith fossil found, with 40 percent of the skeleton recovered.

Questions & Answers

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Igwe Reply
hormon is the chemical messanger
Sneha
21ecological instrument and their diagrams
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Immaculate Reply
kidney stones
Gracelyne
it is a disease that affects the kidney
Miriam
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Gracelyne
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Jackson Reply
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Jackson
hypothesis is a proposed explanation for a phenomenon
Miriam
hypothesis is raw materials
KP
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KP
biology is the study of living things and their interaction with their environment
Miriam
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fatal familial insomnia which affects the thalamus
Miriam
there are other dangerous diseases like CAD i.e coronary artery disease
Miriam
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Thomas Reply
it is any thing that has weight and occupies space
Anye
matter is any substances that occupies spaces and has mass
Jackson
describe photosynthesis
Mavis Reply
What is equilibrium
Mavis
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Mavis
like corporal intern balance right?
FRANCISCA
on my own understanding is just a balanced state
Stanley
photosynthesis is the process by which plants and other organisms convert light energy to chemical energy
Miriam
what is a chromosome?
Wise Reply
Are thread-like structures located inside the nucleus of animal and plant cells.
Canab
thx
Wise
what are the difference between Biotic community and Ecological nitche.
Ganiyat Reply
what is the celll
KAMOLIKA Reply
A cell is the simplest bit of living matter that exist independently
Ganiyat
cell is the basic unit of life
Shadrack
what is ecdysis
Shadrack
what is genetics
Sebastian Reply
The cell is the simplest bit of living matter that can exist independently.
Ganiyat
what happenes when the cell of an organism Is removed?
Isaac Reply
The cell will not function properly
Eunice
what is cell
Maarig Reply
cell is stractural and functional unit of our human body.
Rohini
The study of cells are referred to as?
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Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
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