This document discusses human evolution and key species in the human lineage. It begins by defining evolution and describing how characteristics are passed down and vary within populations. It then summarizes the emergence of key hominin species like Australopithecus, Homo erectus, Neanderthals, and Homo sapiens. For each species, it highlights traits like brain size, locomotion, and anatomical features of the skull, jaws and teeth. It also provides context on the geographic distribution and time period for each species.
2. Evolution is change in the heritable characteristics of
biological populations over successive generations.
These characteristics are the expressions of genes that are passed
on from parent to offspring during reproduction.
Different characteristics tend to exist within any given population
as a result of mutation, genetic recombination and other sources
of genetic variation.
Evolution occurs when evolutionary processes such as natural
selection (including sexual selection) and genetic drift act on this
variation, resulting in certain characteristics becoming more
common or rare within a population.
3. The scientific theory of evolution by natural selection
was conceived independently by Charles
Darwin and Alfred Russel Wallace in the mid-19th
century and was set out in detail in Darwin's book the
Origin of Species.
Human evolution is the evolutionary process that led to
the emergence of anatomically modern humans, beginning
with the evolutionary history of primates—in
particular genus Homo—and leading to the emergence
of Homo sapiens as a distinct species of
the hominid family, which includes the great apes.
This process involved the gradual development of traits
such as human bipedalism and language.
As well as interbreeding with other hominins, which
indicate that human evolution was not linear but a web.
4.
5. Australopithecus, (Latin: “southern ape”)
(genus Australopithecus), group of
extinct primates closely related to, if not actually
ancestors of, modern human beings and known from a
series of fossils found at numerous sites in eastern,
north-central, and southern Africa.
The various species of Australopithecus lived 4.4
million to 1.4 million years ago (mya), during
the Pliocene and Pleistocene epochs (which lasted
from 5.3 million to 11,700 years ago).
6. As characterized by the fossil evidence, members
of Australopithecus bore a combination of human like and ape
like traits.
They were similar to modern humans in that they
were bipedal (that is, they walked on two legs), but, like apes,
they had small brains.
Their canine teeth were smaller than those found in apes, and
their cheek teeth were larger than those of modern humans.
The general term australopith (or australopithecine) is used
informally to refer to members of the genus Australopithecus.
Australopithecines include the genus Paranthropus (2.3–1.2
mya), which comprises three species of australopiths—
collectively called the “robusts” because of their very large
cheek teeth set in massive jaws.
7.
8. Homo erectus, (Latin: “upright man”) extinct species of
the human genus (Homo), perhaps an ancestor of
modern humans (Homo sapiens).
H. erectus most likely originated in Africa, though Eurasia
cannot be ruled out.
Regardless of where it first evolved, the species seems to have
dispersed quickly, starting about 1.9 million years ago (mya)
near the middle of the Pleistocene Epoch, moving through the
African tropics, Europe, South Asia, and Southeast Asia
9. The first fossils attributed to Homo erectus were
discovered by a Dutch army surgeon, Eugène Dubois,
who began his search for ancient human bones on the
island of Java (now part of Indonesia) in 1890.
Dubois found his first specimen in the same year, and in
1891 a well-preserved skullcap was unearthed at Trinil on
the Solo River.
Considering its prominent browridges, retreating
forehead, and angled rear skull, Dubois concluded that the
Trinil cranium showed anatomic features intermediate
between those of humans (as they were then understood)
and those of apes.
10. This history has been recorded directly if imprecisely by
many sites that have yielded fossil remains of H. erectus.
At other localities, broken animal bones and stone tools have
indicated the presence of the species, though there are no
traces of the people themselves.
H. erectus was a human of medium stature that walked
upright. The braincase was low, the forehead was receded,
and the nose, jaws, and palate were wide.
The brain was smaller and the teeth larger than in modern
humans. H. erectus appears to have been the first human
species to control fire, some 1,000,000 years ago.
The species seems to have flourished until some 200,000
years ago (200 kya) or perhaps later before giving way to
other humans including Homo sapiens.
11. Several years later, near where the skull was discovered,
he found a remarkably complete and modern-looking
femur (thighbone).
Since this bone was so similar to a modern human
femur, Dubois decided that the individual to which it
belonged must have walked erect.
He adopted the name Pithecanthropus (coined earlier by
the German zoologist Ernst Haeckel) and called his
discoveries Pithecanthropus erectus (“upright ape-
man”), but the colloquial term became “Java man.”
col*lo*qui*aladjective kə-ˈlō-kwē-əl :used in or
characteristic of familiar and informal conversation; also :
unacceptably informal: using conversational style
12.
13. Neanderthal, (Homo neanderthalensis, Homo sapiens
neanderthalensis), also spelled Neandertal, member of a
group of archaic humans who emerged at least 200,000
years ago during the Pleistocene Epoch (about 2.6
million to 11,700 years ago) and were replaced
or assimilated by early modern human populations
(Homo sapiens) between 35,000 and perhaps 24,000
years ago.
Neanderthals inhabited Eurasia from the Atlantic regions
of Europe eastward to Central Asia, from as far north as
present-day
14. Belgium and as far south as the Mediterranean and
southwest Asia.
Similar archaic human populations lived at the same time
in eastern Asia and in Africa.
Because Neanderthals lived in a land of
abundant limestone caves, which preserved bones well,
and where there has been a long history of prehistoric
research, they are better known than any other archaic
human group.
Consequently, they have become the archetypal
“cavemen.”
The name Neanderthal (or Neandertal) derives from
the Neander Valley (German Neander Thal or Neander
Tal) in Germany, where the fossils were first found.
15. Although Neanderthals possessed much in common
physically with early modern humans, the constellation
of Neanderthal features is unique, with much variation
among individuals as far as craniofacial (head and facial)
characteristics are concerned.
Features of the cranium and lower jaw that were present
more often in Neanderthals than in early and recent
modern humans include a low-vaulted cranium, large
orbital and nasal openings, and prominent arched brow
ridges.
A pronounced occipital region (the rear and base of the
skull) served to anchor the large neck musculature.
16. The cranial capacity of Neanderthals was similar to or
larger than that of recent humans.
The front teeth were larger than those in modern humans,
but the molars and premolars were of a similar size.
The lower jaw displayed a receding chin and was robustly
built.
The mental foramen, a small hole in the skull that allows
nerves to reach the lower jaw, was placed farther back in
Neanderthals than in recent humans, and a space between
the last molar and the ascending edge of the lower jaw
occurred in many individuals.
There was also apparently less lumbar lordosis (back
curvature) in Neanderthals
17.
18. Homo sapiens, (Latin: “wise man”) the species to which
all modern human beings belong. Homo sapiens is one of
several species grouped into the genus Homo, but it is the
only one that is not extinct.
The name Homo sapiens was applied in 1758 by the
father of modern biological classification Carolus
Linnaeus.
Traditionally, this subspecies designation was used by
paleontologists and anthropologists to separate modern
human beings from more-archaic members of Homo
sapiens.
H. s. sapiens is thought to have evolved sometime
between 160,000 and 90,000 years ago in Africa before
migrating first to the Middle East and Europe and later
to Asia, Australia, and the Americas.
19. Currently, H. s. sapiens is the only widely accepted subspecies
of H. sapiens, and the necessity of this designation remains a
matter of debate, since traditional taxonomic practice subdivides
a species only when there is evidence of two or more distinct
subgroups.
Several subspecies of H. sapiens have been proposed. For
example, Swedish naturalist and explorer Carl Linnaeus, in the
10th edition of his Systema Naturae (1758), classified modern
human beings into four subspecies according to geographic
origin: H. s. asiaticus, H. s. europaeus, H. s. afer, and H. s.
americanus.
Linnaeus’s classification was later discarded because of the
recognition of racial prejudice and outdated notions of European
superiority implicit in his taxonomy and because of discoveries
that only superficial differences existed between these groups
20. the earliest Homo sapiens had bodies with short, slender
trunks and long limbs. These body proportions are an
adaptation for surviving in tropical regions due to the
greater proportion of skin surface available for cooling the
body. More stocky builds gradually evolved when
populations spread to cooler regions, as an adaptation that
helped the body retain heat.
Modern humans now have an average height of about 160
centimetres in females and 175 centimetres in males.
Brain
Homo sapiens living today have an average brain size of
about 1350 cubic centimetres which makes-up 2.2% of our
body weight. Early Homo sapiens, however, had slightly
larger brains at nearly 1500 cubic centimetres.
21. Skull
modern Homo sapiens skulls have a short base and a high braincase. Unlike
other species of Homo, the skull is broadest at the top. The fuller braincase
also results in almost no post-orbital constriction or narrowing behind the eye
sockets
back of the skull is rounded and indicates a reduction in neck muscles
face is reasonably small with a projecting nose bone
brow ridge is limited and the forehead is tall
orbits (eye sockets) are square rather than round
Jaws and teeth
jaws are short which result in an almost vertical face
usually no gap (retromolar space) between the last molar teeth and the jaw
bone
jaws are lightly built and have a protruding bony chin for added
strength. Homo sapiens is the only species to have a protruding chin.
shortened jaw has affected the arrangement of the teeth within the jaw. They
are now arranged in a parabolic shape in which the side rows of teeth splay
outwards rather than remain parallel as in our earliest long jawed ancestors.
teeth are relatively small compared with earlier species. This is especially
noticeable in the front incisor and canine teeth.
front premolar teeth in the lower jaw have two equal-sized cusps (bumps on
the chewing surface
