FREE ESSAY ON HOMINID SPECIES

HOMINID SPECIES

Hominid Species
The time of the split between humans and living apes used to be thought to have occurred
15 to 20 million years ago, or even up to 30 or 40 million years ago. Some apes occurring
within that time period, such as Ramapithecus, used to be considered as hominids, and
possible ancestors of humans. Later fossil finds indicated that Ramapithecus was more
closely related to the orang-utan, and new biochemical evidence indicated that the last
common ancestor of hominids and apes occurred between 5 and 10 million years ago, and
probably in the lower end of that range. Ramapithecus therefore is no longer considered a
hominid. The species here are listed roughly in order of appearance in the fossil record
(note that this ordering is not meant to represent an evolutionary sequence), except that
the robust australopithecines are kept together.
Ardipithecus ramidus
It is the oldest known hominid species, found in the Middle Awash region of Ethiopia in
1994 by Tim White and dated at 4.4 million years. Most remains are skull fragments.
Indirect evidence suggests that it was possibly bipedal, and that some individuals were
about 122 cm (4'0) tall. The teeth are intermediate between those of earlier apes and A.
afarensis, but one baby tooth is very primitive, resembling a chimpanzee tooth more than
any other known hominid tooth. Other fossils found with ramidus indicate that it may have
been a forest dweller. This may cause modification of current theories about why hominids
became bipedal, which often link bipedalism with a move to a savannah environment. 
Australopithecus anamensis
This species was found in 1994 by Maeve Leakey in Kanapoi and Allia Bay situated in North
Kenya. The material consists of 9 fossils, mostly found in 1994, from Kanapoi, and 12
fossils, mostly teeth found in 1988, from Allia Bay. Anamensis existed between 4.2 and
3.9 million years ago, and has a mixture of primitive features in the skull, and advanced
features in the body. The teeth and jaws are very similar to those of older fossil apes.
A partial tibia is strong evidence of bipedality, and a lower humerus is extremely
humanlike. 
Australopithecus afarensis
A. afarensis existed between 3.9 and 3.0 million years ago. The first of its fossils were
found in the mid 1970s along the East African Rift valley. Afarensis had an apelike face
with a low forehead, a bony ridge over the eyes, a flat nose, and no chin. They had
protruding jaws with large back teeth. Cranial capacity varied from about 375 to 550 cc.
The skull is similar to that of a chimpanzee, except for the more humanlike teeth. The
canine teeth are much smaller than those of modern apes, but larger and more pointed than
those of humans, and shape of the jaw is between the rectangular shape of apes and the
parabolic shape of humans. However their pelvis and leg bones far more closely resemble
those of modern man, and leave no doubt that they were bipedal. Their bones show that
they were physically very strong. Females were substantially smaller than males, a sexual
dimorphism. Height varied between about 107 cm (3'6) and 152 cm (5'0). The finger and toe
bones are curved and proportionally longer than in humans, but the hands are similar to
humans in most other details. Most scientists consider this evidence that afarensis was
still partially adapted to climbing in trees, others consider it evolutionary baggage. 
Australopithecus africanus
A. africanus was found by Raymond Dart in 1925 in a limestone quarry (Tuang) in South
Africa. Africanus existed between 3 and 2 million years ago. It is similar to afarensis,
and was also bipedal , but body size was slightly greater. Brain size may also have been
slightly larger, ranging between 420 and 500 cc. This is a little larger than chimp
brains (despite a similar body size), but still not advanced in the areas necessary for
speech. The back teeth were a little bigger than in afarensis. Although the teeth and
jaws of africanus are much larger than those of humans, they are far more similar to
human teeth than to those of apes. The shape of the jaw is now fully parabolic, like that
of humans, and the size of the canine teeth is smaller compared to afarensis. 
Australopithecus garhi
This species was named in April 1999. It is known from a partial skull. The skull differs
from previous australopithecine species in the combination of its features, notably the
extremely large size of its teeth, especially the rear ones, and a primitive skull
morphology. Some nearby skeletal remains may belong to the same species. They show a
humanlike ratio of the humerus and femur, but an apelike ratio of the lower and upper
arm. Australopithecus afarensis and africanus, and the other species above, are known as
gracile (slender) australopithecines, because of their relatively lighter build,
especially in the skull and teeth. Despite this, they were still more robust than modern
humans. 
Australopithecus aethiopicus
A. aethiopicus existed between 2.6 and 2.3 million years ago. This species is known from
one major specimen, the Black Skull discovered by Alan Walker in 1985, and a few other
minor specimens which may belong to the same species. It may be an ancestor of robustus
and boisei, but it has a confusing mixture of primitive and advanced traits. The brain
size is very small, at 410 cc, and parts of the skull, particularly the back portions,
are very primitive, most resembling afarensis. Other characteristics, like the
massiveness of the face, jaws and single tooth found, and the largest sagittal crest (a
bony ridge on top of the skull to which chewing muscles attach) in any known hominid, are
more like that of A. boisei.
Australopithecus robustus
A. robustus had a body similar to that of africanus, but a larger and more robust skull
and teeth. It existed between 2 and 1.5 million years ago. The massive face is flat or
dished, with no forehead and large brow ridges. It has relatively small front teeth, but
massive grinding teeth in a large lower jaw. Most specimens have sagittal crests. Its
diet would have been mostly coarse, tough food that needed a lot of chewing. The average
brain size is about 530 cc. Bones excavated with robustus skeletons indicate that they
may have been used as digging tools. 
Australopithecus boisei (was Zinjanthropus boisei)
A. boisei was found at Lake Turkana, Northern Kenya and existed between 2.1 and 1.1
million years ago. It was similar to robustus, but the face and cheek teeth were even
more massive, some molars being up to 2 cm across. The brain size is very similar to
robustus, about 530 cc. Some consider boisei and robustus to be variants of the same
species. Australopithecus aethiopicus, robustus and boisei are known as robust
australopithecines, because their skulls are more heavily built. However, in the same
sedimentary layer, another cranium was also found belonging to a species of hominid named
Homo ergaster. This hominid species is believed to be a different geographical population
of Homo erectus 
Homo habilis
H. habilis, handy man, was so called because of evidence of tools found with its remains
by the Leakeys in1961. Habilis existed between 2.4 and 1.5 million years ago. It is very
similar to australopithecines in many ways. The face is still primitive, but it projects
less than in A. africanus. The back teeth are smaller, but still larger than in modern
humans. The average brain size, at 650 cc, is considerably larger than in
australopithecines. Brain size varies between 500 and 800 cc, overlapping the
australopithecines at the low end and H. erectus at the high end. The brain shape is also
more humanlike. The bulge of Broca's area, essential for speech, is visible in one
habilis brain cast, and indicates it was possibly capable of rudimentary speech. Habilis
is thought to have been about 127 cm (5'0) tall, and about 45 kg (100 lb) in weight,
although females may have been smaller. 
Homo erectus
H. erectus was first found by Eugene Dubois in 1881 and existed between 1.8 million and
300,000 years ago. Like habilis, the face has protruding jaws with large molars, no chin,
thick brow ridges, and a long low skull, with a brain size varying between 750 and 1225
cc. Early erectus specimens average about 900 cc, while late ones have an average of
about 1100 cc. The skeleton is more robust than those of modern humans, implying greater
strength. Body proportions vary; the Turkana Boy is tall and slender (though still very
strong), like modern humans from the same area, while the few limb bones found of Peking
Man indicate a shorter, sturdier build. Studys of the Turkana Boy skeleton indicate that
erectus may have been more efficient at walking than modern humans, whose skeletons have
had to adapt to allow for the birth of larger-brained infants. Homo habilis and all the
australopithecines are found only in Africa, but erectus was wide-ranging, and has been
found in Africa, Asia, and Europe. There is evidence that erectus probably used fire, and
their stone tools are more sophisticated than those of habilis. 
Homo sapiens (archaic)
Archaic forms of Homo sapiens first appear about 500,000 years ago. The term covers a
diverse group of skulls which have features of both Homo erectus and modern humans. The
brain size is larger than erectus and smaller than most modern humans, averaging about
1200 cc, and the skull is more rounded than in erectus. The skeleton and teeth are
usually less robust than erectus, but more robust than modern humans. Many still have
large brow ridges and receding foreheads and chins. There is no clear dividing line
between late erectus and archaic sapiens, and many fossils between 500,000 and 200,000
years ago are difficult to classify as one or the other. 
Homo sapiens neanderthalensis (was Homo neanderthalensis)
Neandertal man existed between 230,000 and 30,000 years ago and was found in the Neander
Valley in Germany in 1856. The average brain size is slightly larger than that of modern
humans, about 1450 cc, but this is probably correlated with their greater bulk. The brain
case however is longer and lower than that of modern humans, with a marked bulge at the
back of the skull. Like erectus, they had a protruding jaw and receding forehead. The
chin was usually weak. The midfacial area also protrudes, a feature that is not found in
erectus or sapiens and may be an adaptation to cold. Neandertals mostly lived in cold
climates, and their body proportions are similar to those of modern cold-adapted peoples:
short and solid, with short limbs. Men averaged about 168 cm (5'6) in height. Their bones
are thick and heavy, and show signs of powerful muscle attachments. Neandertals would
have been extraordinarily strong by modern standards, and their skeletons show that they
endured brutally hard lives. A large number of tools and weapons have been found, more
advanced than those of Homo erectus. Neandertals were formidable hunters, and are the
first people known to have buried their dead, with the oldest known burial site being
about 100,000 years old. They are found throughout Europe and the Middle East.
Homo sapiens sapiens (modern)
Modern forms of Homo sapiens first appear about 120,000 years ago. Modern humans have an
average brain size of about 1350 cc. The forehead rises sharply, eyebrow ridges are very
small or more usually absent, the chin is prominent, and the skeleton is very gracile.
About 40,000 years ago, with the appearance of the Cro-Magnon culture, tool kits started
becoming markedly more sophisticated, using a wider variety of raw materials such as bone
and antler, and containing new implements for making clothing, engraving and sculpting.
Fine artwork, in the form of decorated tools, beads, ivory carvings of humans and
animals, clay figurines, musical instruments, and spectacular cave paintings appeared
over the next 20,000 years.