Text Version of Human Evolution Activity

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Text Version of Human Evolution Activity
Ardipithecus ramidus
The most primitive hominid yet found, this species has more chimpanzee-like
features than any other human ancestor. Ardipithecus ramidus may have walked
upright. Other fossils discovered with A. ramidus suggest that the species lived in
the forest.
4.4 mya
first fossils found 1992
Australopithecus anamensis
Exhibiting some chimp-like characteristics, A. anamensis' jaws are more
primitive than those of later hominids. And yet, its humerus (an arm bone) is
quite human-like. Characteristics of its tibia (a lower leg bone) indicate that A.
anamensis walked on two feet.
4.2 - 3.9 mya
first fossil found 1965
Australopithecus afarensis
This species includes "Lucy," the 3.2 million year old fossil found by Donald
Johanson. A. afarensis' small braincases and relatively large teeth and chewing
muscles are similar to those of chimpanzees. However, their teeth, as well as their
leg and pelvis bones, exhibit human-like characteristics. They ranged in height
from three and a half feet to five feet and walked upright.
3.5 - 2.9 mya
first fossils found 1973
Australopithecus africanus
Although similar in many ways to A. afarensis, this species had a slightly larger
brain (but still only slightly larger than a chimp's brain), smaller canine teeth, and
larger molars. The wear of the teeth suggests that A. africanus ate fruits and
foliage.
3.0 - 2.4 mya
first fossils found 1924
Australopithecus robustus
Believed to be roughly the same size as A. afarensis, A. robustus had a large,
"robust" (heavier, thicker) skull, as well as a jaw and large teeth that were well
adapted to chewing. Like some present-day apes, this species had a "sagittal
crest" (a ridge running from front to back on the top of the skull) from which
muscles running to the jaw were attached.
2.1 - 1.6 mya
first fossil found 1938
Australopithecus boisei
A. boisei is similar to A. robustus, except that its skull and teeth are even larger.
Some experts consider the two closely related, both branching from another
species called A. aethiopicus. Others believe A. robustus evolved from A.
africanus. Like all of the other Autralopithecus species, A. boisei walked upright.
2.3 - 1.1 mya
first fossil found 1959
Homo habilis
Homo habilis, which actually means "handy man," is apparently the first species
to make and use primitive stone tools. About five feet tall and weighing 100
pounds, H. habilis had a brain that was larger than the largest Autralopithecus
brain, but smaller than the Homo erectus brain.
2.4 - 1.5 mya
first fossil found 1960
Homo erectus
The first example of Homo erectus, known as "Java Man," was discovered in
Indonesia in 1893. Fossil remains of Homo erectus have since been found
throughout Africa and Asia, making it the first wide-ranging hominid. Despite the
primitive appearance of its skull, the erectus skeleton is very similar to that of
modern humans, although more robust (thicker and heavier). Homo erectus was
probably the first hominid to use fire.
1.8 mya - 300,000 years ago
first fossil found in 1893
Homo sapiens (archaic)
Also known as Homo heidelbergensis, this species has a brain that was larger
than H. erectus' and smaller than that of a modern human. The brain was enclosed
in a skull that was more rounded than H. erectus'. Fossil remains of archaic Homo
sapiens have been found in Africa and Europe.
500,000 - 200,000 years ago
first fossil found in 1921
Homo sapiens neanderthalensis
Averaging five and a half feet in height and possessing short limbs, Neanderthals
were well-adapted to living in a cold climate. Attached to their robust (thick and
heavy) bones were powerful muscles. The Neanderthal's brain was larger than the
brain of living humans, although its shape was longer from front to back and not
as rounded in the front.
230,000 - 30,000 years ago
first fossil found in 1856
Homo sapiens (modern)
Modern Homo sapiens, also known as Homo sapiens sapiens, have been around
for the past 120,000 years. Homo sapiens living about 40,000 years ago made
elaborate tools out of bone, antler, ivory, stone, and wood, and produced fine
artwork in the form of carvings and cave paintings.
120,000 years ago - present
first "Cro-Magnon" specimens found in 1868
Lucy in the Earth
Discovered in 1974 by Donald Johanson, Lucy is special because she lived
so long ago (3.2 millions years) and because almost half of her skeleton was
found. (Most fossil finds are just fragments -- sometimes a tooth or a piece
of a skull.) Johanson named her after the Beatles' song, "Lucy in the Sky
with Diamonds."
Not far from the Lucy site, another significant find was made, this one also
by Donald Johanson. Known as "The First Family," the find consisted of
many fossils that originated from at least thirteen individuals. The evidence
indicates that the thirteen died together some 3.2 million years ago, possibly
in a flash flood. This is the first evidence of an ancient species living in
groups.
Fossilized Footprints
How do we know if an early ape-man or woman walked upright? An
examination of certain bones -- a tibia (leg bone) or a pelvis, for
example -- can reveal the answer. So can fossilized footprints.
In 1976, members of a team led by Mary Leakey discovered the
fossilized footprints of human ancestors in Laetoli, Africa. The
footprints were formed 3.5 million years ago when at least two
individuals walked over wet volcanic ash. The wet ash hardened like
cement and was then covered by more ash.
The footprints show that the individuals had perfect, two-footed
strides. They also reveal that one hominid was larger than the other.
And because the
footprints fall next to
each other, they indicate that the two hominids were
walking side by side and close enough to each other
to be touching.
Apes sometimes walk on two legs. How, then, can
we be sure that the footprints weren't left by a
couple of apes that decided to walk upright for a few
yards? When an ape walks upright, weight is
transmitted from the heel, along the outside of the foot, and then through the middle toes. A
human foot transmits weight from the heel, along the outside of the foot, across the ball of the
foot, and finally through the big toe -- this is a much more efficient way to transfer energy when
walking upright. The imprints left behind at Laetoli clearly show the weight distribution of true
upright walkers.
The footprints also look remarkably like a human's. In fact, they looked so human-like, some
scientists had a hard time believing that they were made by Australopithecus afarensis (Lucy's
species), the only human ancestor known to have lived at the time.
Taung Child
In the distant past, perhaps seven million years ago, chimpanzees and hominids branched from a
shared ancestor. The hominids evolved and branched into at least twelve distinct species. Today,
only one kind of hominid remains: Homo sapiens sapiens.
The story of human evolution has emerged slowly over the century. The first significant
discovery was that of the "Taung child" in 1925. Found in South Africa, the skull belonged to a
child who was at a stage of development of a present-day six year old. (Early hominids, such as
the Australopithecines, grew at a faster rate than modern humans.) This fossilized skull was the
first Autralopithecus specimen. With a brain larger than a chimp's but smaller than a human's, it
was a true missing link.
Raymond Dart, the discoverer of the Taung child, realized its significance. But because the
skulls of young humans and young apes are so similar, and because the skull was so different
from other found fossils, including the phony Piltdown Man, other scientists ignored the find as
well as Dart's interpretation. With the discovery of several more Australopithecus fossils in 1936
and 1947, this time of adult specimens, Dart's view began to see acceptance.
Libby introduces radiocarbon dating
1947
In 1940 Martin Kamen discovered radioactive carbon-14 (an isotope of carbon) and found that it
had a half-life of about 5,700 years. Scientists had also found that some of the nitrogen in the
atmosphere was turned into carbon-14 when hit with cosmic rays. Thus, an equilibrium was
reached, the newly formed carbon-14 replacing the carbon-14 that decayed, so that there was
always a small amount in the atmosphere.
In 1947 American chemist Willard Libby (1908-1980) figured that plants would absorb some of
this trace carbon-14 while they absorbed ordinary carbon in photosynthesis. Once the plant died,
of course, it couldn't absorb any more carbon of any kind, and the carbon-14 it contained would
decay at its usual rate without being replaced. By finding the concentration of carbon-14 left in
the remains of a plant, you could calculate the amount of time since the plant had died. With this
technique scientists could determine the age of plant-based artifacts -- wood, parchment, textiles
-- up to 45,000 years old. This has allowed estimates of the age of Egyptian mummies,
prehistoric dwellings, and so forth.
For his work on carbon-14 dating, Libby received the Nobel Prize in chemistry in 1960
4.4 million-year-old human ancestor is found
1994
Tim White, Berhane Asfaw, and Gen Suwa, who have long worked together unearthing and
analyzing fossils in Africa, made a new and remarkable discovery in 1993. In Ethiopia, they
found hominid skull, jaw, and arm bones plus a few teeth that dated back to 4.4 million years
ago. That would make these the oldest hominid ancestors yet identified, and the most primitive
hominid species known.
Announcing these fossils in 1994, the group named them Australopithecus ramidus, putting them
in the same genus as the 1.75-million-year-old Australopithecus boisei and the 3-million-yearold "Lucy." But eight months later, the researchers changed the name to Ardipithecus ramidus,
moving the species represented by the fossils into a different genus. They did not fully explain
the change, but were continuing to analyze the fossils and planned publication of their findings
within a few years. (According to naming convention, discoverers have the right to name the
species, but acceptance of the genus they suggest depends upon the agreement of other workers
in the field.)
The species looked to be a link between ancient African apes and Australopithecus.It shared
physical features of both groups. Paleontologists Meave Leakey and Alan Walker write that
"Ardipithecus, with its numerous chimplike features, appears to have taken the human fossil
record back close to the time of the chimp-human split."
Discussion continues over whether Ardipithecus is a hominid or not, whether it walked on two
feet or not, and what its relationship is to the 3.9Ð4.2 million year old fossils found in 1995 by
Meave Leakey and Alan Walker in Kenya (Australepithecus anamensis). These latter show clear
signs of walking upright and of living in a wooded area, throwing into doubt the usual
explanation of bipedalism as an adaptation to living in the savannah. These recent discoveries
provide important evidence in the search for human origins, but points out Walker, "As with so
many scientific discoveries, this one also provokes more fascinating questions."
Piltdown Man is revealed as fake
1953
"Piltdown Man Hoax Is Exposed," announced the New York Times on November 21, 1953.
"Part of the skull of the Piltdown man, one of the most famous fossil skulls in the world, has
been declared a hoax by authorities at the British Natural History Museum," the article said.
The Piltdown fossils, including a portion of the skull, a jawbone, and a few teeth, were found in
1911 and 1912. This "Piltdown Man" was believed by many to be "the earliest Englishman," and
in fact, the missing link between apes and humans. But in 1953, the jawbone was found to be
that of a modern ape -- orangutan, most likely -- that had been treated with chemicals to make it
look as though it had been lying in the ground for hundreds of centuries. The cap of the skull was
still thought to be a genuine fossil, but far more recent than originally believed.
"This declaration . . . has been made after twenty years of rumors and uneasy speculation among
European paleontologists about the authenticity of the bones," the New York Times stated. The
London Star headlines shouted, "The Biggest Scientific Hoax of the Century!"
It was big. Several highly respected and serious scientists were deceived and their reputations
forever tarnished, and years of research and thought had been wasted on trying to analyze and fit
the fake fossils into the record of human evolution. The relics were said to have been found in
Piltdown, England by workers digging a pit. They handed over the bones to Charles Dawson, a
lawyer and amateur geologist. He recruited the help of Arthur Woodward Smith, Tielhard de
Chardin, Arthur Keith, and other notable scientists, who were very excited about the find. It was
easy for them to believe that the bones, a very thick skull about the size of a modern human's and
a large, apelike jaw, were part of the same individual because that physiology was what they
expected from a "missing link." It also suited them -- perhaps subconsciously -- because it was
found in England.
The New York Times in 1953 further reported, "Sir Arthur Keith, famous British paleontologist,
spent more than five years piecing together the fragments of what he called a 'remarkable'
discovery. He said the brain case was 'primitive in some respects but in all its characteristics
distinctly human.' The Piltdown man was named Eoanthropus dawsonii, or Dawn man, in honor
of its discoverer, and paleontologists throughout the world handled it with reverence.
"Although the fossil was generally accepted as the earliest known specimen of sapient man, as
opposed to the apeman of China and Java, many research workers reserved their opinions about
the disputatious jawbone."
Actually, Piltdown Man threw a wrench into the works of investigating human evolution. In
1925, Raymond Dart found the Taung skull, a fossil in South Africa that he believed was the
earliest human ancestor (now known as Australopithecus). But few people accepted his find; it
didn't fit in with Piltdown, for one thing. It had a small brain, yet a human-like jaw. But mostly,
it came from Africa, and many European scientists preferred to have England be the cradle of
humanity. Dart was ultimately proved correct.
Around 1939, paleontologist Kenneth Oakley devised a new chemical analysis called fluorine
testing. Fossil bones absorb fluorine from soil and water, so fossils that have been in the same
soil for the same amount of time should have roughly the same amount of fluorine. To
authenticate that the jaw and skull of Piltdown Man belonged together, the Natural History
Museum had Oakley, a scientist uninvolved in Piltdown's discovery, test them in 1949. As it
turned out, the remains seemed to have similar amounts of fluorine, suggesting they belonged
together, but surprisingly they appeared to be much younger than was originally thought -perhaps only 50,000 instead of 500,000 years old. This made matters even more confusing, since
there were fossil examples of modern humans from 50,000 years ago. That would have made
Piltdown Man a freakish throwback, not a missing link.
In 1953, Joseph Weiner, an Oxford professor of physical anthropology, met Kenneth Oakley at a
banquet. They got chatting about the Piltdown puzzle and Weiner couldn't get it out of his mind.
He had reports on the research and casts of the fossils and began examining each minutely. He
was amazed to see that the fossil teeth seemed to have been deliberately ground down with
something abrasive to give them a unique wear pattern. He called Oakley, who had access to the
real fossils and asked him to look at them with a magnifier. He too became convinced the teeth
had been purposely changed to fit the Piltdown Man. Weiner and Oakley now undertook new
chemical analyses, including an improved fluorine test, and found that the jaw and teeth were not
the same age as the skull and were not even fossils, just old bones. Some of the bones had been
stained with chemicals and some with ordinary paint to make them match each other and the
color of the soil where they were found. Weiner, Oakley, and Oxford anthropologist Wilfrid Le
Gros Clark were now certain that the Piltdown fossil collection was a fake, and not just that, but
a hoax.
On November 20, 1953, they reported their findings in the bulletin of the Natural History
Museum. The scientists of 40 years before, they explained, had been victims of "a most elaborate
and carefully prepared hoax. The faking of the mandible [jawbone]," they wrote, "is so
extraordinarily skillful and the perpetration of the hoax appears to have been so entirely
unscrupulous and inexplicable as to find no parallel in the history of paleontological discovery."
The newspaper headlines the following day shared the story with the world. At that time, the
skullcap was still believed to be about 50,000 years old. In 1959, however, the recently
discovered carbon-14 dating technique was used to show that it was between 520 and 720 years
old, the jawbone slightly younger! While different individuals have been accused of being the
perpetrator of the hoax, there is no agreement upon who it might have been
Johanson finds 3.2 million-year-old Lucy
1974
Photo: X-ray photo of the "Lucy" skeleton
In 1973, Donald Johanson was in the Afar, part of the Hadar region of Ethiopia, with the
International Afar Research Expedition. He made a dramatic fossil find -- the leg bones of 3million-year-old hominid. The bones' size and shape indicated that this individual walked
upright, making it the oldest hominid on record to do so. This discovery helped Johanson raise
enough money to continue the expedition in the Afar.
On November 30, 1974, Johanson and another member of the expedition discovered small bones
from one individual -- it was a hominid, but looked different from any they were familiar with.
Everyone at the site joined in the search for more of this specimen and collected hundreds of
pieces. The pieces did appear to be from the same individual, and made up 40 percent of a
skeleton. The pelvis showed it had been a female, and the team named her Lucy after the Beatles'
song "Lucy in the Sky with Diamonds."
Lucy had a small brain and was only about one meter tall. Since bones from both left and right
sides were found, mirror images could be constructed to put together 70 percent of her skeleton.
More than one dating technique put her age at about 3.5 million years. (Johanson's earlier leg
bone find was dated at 4 million years old.) The team kept working at the site and found other,
more modern hominids together with stone tools. By 1976, however, Ethiopia's political situation
was unstable, making further excavations unsafe or impossible.
In 1978, Mary Leakey discovered ancient footprints preserved in the ground around what was
once a water hole at Laetoli, Tanzania. These prints showed clearly that small primates walked
on two feet there. This put upright walking even further back in time.
Johanson and his colleague Tim White compared Leakey's finds at Laetoli with theirs from Afar,
and felt that they were very similar, probably representing a stage between apes and humans.
They categorized them both as Australopithecus afarensis. Leakey disagreed, but both of their
finds broke a long-standing assumption: that humans developed big brains before walking
upright. After 1974, scientists realized that this wasn't necessarily true, and that brain size
overlaps between types of hominids, even as modern people's brains vary in size without relation
to intelligence. This meant they had to look again at why hominids started walking upright. It
had been thought that the big-brained creatures started using tools, and to free up their hands,
they had to walk upright. But Lucy walked on two feet, and even had "modern" hands, yet
showed no evidence of using tools.
Opponents of Johanson and White's theory think the Homo genus had a separate lineage from
other primates. Johanson acknowledged that his explanation would be subject to change with
new evidence.
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