Human evolution is the
phenotypic history of the genus
Homo, including the emergence of
Homo sapiens as a distinct
species and as a unique category of
hominids ("great apes") and
mammals. The study of human
evolution uses many
scientific disciplines, including
physical anthropology,
primatology,
archaeology,
linguistics and
genetics.
[1] The term "human" in the context of human evolution refers to the genus
Homo, but studies of human evolution usually include other
hominids,
such as the
Australopithecines, from which the genus
Homo had diverged by about 2.3 to 2.4 million years ago in Africa.
[2][3] Scientists
have estimated that humans branched off from their common ancestor with
chimpanzees about 5–7 million years ago. Several species and subspecies of
Homo evolved and are now
extinct,
introgressed or
extant. Examples include
Homo
erectus (which
inhabited Asia, Africa, and Europe) and
Neanderthals (either
Homo neanderthalensis or
Homo sapiens neanderthalensis) (which inhabited Europe and Asia).
Archaic Homo sapiens evolved between 400,000
and 250,000 years ago.
The dominant view among scientists concerning the origin of
anatomically
modern humans is the hypothesis known as "Out of Africa",
recent African origin of modern humans, ROAM, or
recent African origin hypothesis,
[4][5][6] which
argues that
Homo sapiens arose in Africa and migrated out of the
continent around 50,000 to 100,000 years ago, replacing populations of
Homo
erectus in Asia and Neanderthals in Europe.
Scientists supporting an alternative
multiregional
hypothesis argue that
Homo sapiens evolved as geographically
separate but interbreeding populations stemming from a worldwide migration of
Homo erectus out of Africa nearly 2.5 million years ago. Evidence
suggests that Neanderthal genomes may have contributed about 4% of non-African
heredity, and the recently discovered
Denisova hominin may have contributed 6% of the
genome of
Melanesians.
[7][8] Archaic
genetic contribution
contradicts total Eurasian replacement around 100,000
years ago.
History of ideas
The word
homo, the name of the biological genus to which humans
belong, is
Latin for "human". It was chosen originally by
Carolus Linnaeus in his classification system. The
word "human" is from the Latin
humanus, the adjectival form of
homo. The Latin "homo" derives from the Indo-European root,
*
dhghem, or "earth".
[10] Carolus Linnaeus and other scientists of his time also considered the
great apes to be the closest relatives of humans due
to
morphological and
anatomical similarities. The possibility of linking
humans with earlier apes by descent only became clear after 1859 with the
publication of
Charles Darwin's
On
the Origin of Species. This argued for the idea of the evolution
of new species from earlier ones. Darwin's book did not address the question of
human evolution, saying only that "Light will be thrown on the origin of man and
his history".
The first debates about the nature of human evolution arose between
Thomas Huxley and
Richard Owen. Huxley argued for human evolution from
apes by illustrating many of the similarities and differences between humans and
apes, and did so particularly in his 1863 book
Evidence as to Man's Place in Nature. However,
many of Darwin's early supporters (such as
Alfred Russel Wallace and
Charles
Lyell) did not agree that the origin of the mental capacities and the
moral sensibilities of humans could be explained by
natural selection. Darwin applied the theory of
evolution and
sexual selection to humans when he published
The Descent of Man in 1871.
[11] A major problem at that time was the lack of fossil intermediaries. Despite
the discovery by
Eugene Dubois of what is now called
Homo
erectus in
1891 at
Trinil,
Java, it was only in the 1920s that such
fossils were discovered in Africa, that
intermediate species began to accumulate. In 1925,
Raymond Dart described
Australopithecus
africanus. The
type specimen was the
Taung Child, an Australopithecine infant discovered
in a cave. The child's remains were a remarkably well-preserved tiny skull and
an
endocranial cast of the individual's brain. Although
the brain was small (410 cm³), its shape was rounded, unlike that of chimpanzees
and gorillas, and more like a modern human brain. Also, the specimen showed
short
canine
teeth, and the position of the
foramen magnum was evidence of
bipedal locomotion. All of these traits convinced Dart that the Taung baby was a bipedal
human ancestor, a transitional form between apes and humans.
The
classification of humans and their relatives has
changed considerably over time. The gracile Australopithecines are now thought
to be ancestors of the genus
Homo, the group to which modern humans
belong. Both Australopithecines and
Homo sapiens are part of the tribe
Hominini.
Recent data suggests Australopithecines were a diverse group and that
A.
africanus may not be a direct ancestor of modern humans. Reclassification of
Australopithecines that originally were split into either
gracile or
robust varieties has put the latter into a genus of
its own,
Paranthropus. Taxonomists place humans,
Australopithecines and related species in the same family as other great apes,
in the
Hominidae.