Encyclopedia of Evolution.pdf - Online Reading Center

sils. When he inquired again, they gave him a fossilized bone
they had found and which he identified as a fragment of parietal
bone, from the upper side of a humanlike skull. Later,
Dawson himself found another bone in the quarry, this time
a piece of frontal bone from a humanlike skull. He contacted
prominent British paleontologist Arthur Smith Woodward,
who looked at the fossils himself in 1912. At the quarry, they
were joined by the young French cleric and amateur archaeologist
Teilhard de Chardin (see Teilhard de Chardin,
Pierre). As radiometric dating techniques had not been
developed, it was unclear just how ancient the Piltdown gravel
was. Teilhard de Chardin found an elephant tooth, which
demonstrated the antiquity of the gravels, since elephants lived
in what is now England many thousands of years earlier when
the climate had been tropical. But it was Dawson who just
happened to find yet another piece of humanlike skull. The
three investigators kept finding more skull fragments, which
happened to fit perfectly together. Then, with a single stroke
of his geologist’s hammer, Dawson sent a fossil jawbone flying
into the air. All of the pieces of bone were stained with iron,
like much of the gravel in which they were found. The similarity
of staining convinced the investigators that all the pieces
belonged to the same skull. This could have been proven if the
part of the jawbone that articulates with the skull had been
preserved, but it was missing.
An exciting announcement of the discovery emerged in
the newspapers before Dawson and Smith Woodward presented
the actual fragments for other scientists to observe, at
the 1912 meeting of the British Geological Society in December.
The premature public announcement may have influenced
the scientists in attendance toward believing Dawson.
The reconstructed skull astounded everyone. The brain was
somewhat small but well within the modern human range.
The jawbone was U-shaped like that of an ape, rather than
V-shaped like a human jaw; and the two remaining teeth also
appeared to be very apelike. If this were the case, the scientists
concluded, then Piltdown man must have lived long before
the Neandertals (as Piltdown man had a more primitive jaw).
Both Neandertals and Java man must have been sidelines of
evolution, lineages that never developed into modern humans
and eventually became extinct (which turned out to be true,
but was the only correct conclusion these scientists reached).
Human evolution, it appeared to them, began with the brain
and began in what is now England. They named Piltdown
man Eoanthropus dawsoni, or Dawson’s dawn-man.
Some doubts remained. German anthropologist Franz
Weidenreich said the jawbone looked an awful lot like that
of an orangutan. Smith Woodward said that if only they had
been able to find a canine tooth, then they could be more
certain that Piltdown man really was intermediate between
humans and apes. Smith Woodward predicted that this tooth
would be intermediate between the large canine tooth of an
ape and the small canine tooth of a human. In the 1913 season
in the quarry, Teilhard de Chardin found exactly this
tooth, and it looked exactly as Smith Woodward had predicted.
The tooth was stained just like the other fragments.
For four decades, Dawson’s name was enshrined among
the great investigators of human evolution. In 1953 investiga-
plate tectonics
tors revealed that all of the bones were recent in age, and had
been stained to look old; some had even been filed to have
a convincing shape. The skull fragments were from a modern
human, and the jawbone was, as Weidenreich had suspected,
from an orangutan. Some historians have suggested
that Dawson intended Piltdown as a joke, not a serious hoax,
and that he planned to show the world how scientists can be
as gullible as anyone else. Historians will never know what
he intended to do, as he was killed in 1917 in World War I.
Evolutionary biologist Stephen Jay Gould suggested that Teilhard
de Chardin was also involved in the hoax; this, also, will
remain unknown.
For most scientists and historians, the Piltdown episode
remains an interesting story of how investigators need to be
skeptical when new evidence appears to contradict previous
evidence; as many scientists say, extraordinary claims require
extraordinary evidence. Creationists keep the Piltdown story
very much alive, implying that the entire fossil record of
humans is a patchwork of unreliable fragments and, quite
possibly, hoaxes (see creationism). An episode such as the
Piltdown affair could not happen today. Microscopic, chemical,
and radiometric methods available today would immediately
reveal a modern Piltdown to be filed, stained, and
modern.
Further Reading
Gould, Stephen Jay. “Teilhard and Piltdown.” Section 4 in Hen’s
Teeth and Horse’s Toes. New York: Norton, 1983.
Walsh, John Evangelist. Unraveling Piltdown: The Science Fraud of
the Century and Its Solution. New York: Random House, 1996.
plate tectonics The movement of the crustal plates of the
Earth’s surface is called plate tectonics. The Earth’s surface
is fractured into eight major plates and several smaller ones
(see figure on page 316), which move relative to one another.
The plates appear to be propelled by flowing magma underneath
the surface. The ocean floors are formed of heavier
material, while the continents, formed of lighter rocks, sit on
the surfaces of the heavier rocks. The lighter continental rock
accumulated during Earth’s early history, especially during
the Archaean Eon about 3 billion years ago. Plate tectonics is
now understood as the driving force of continental drift.
The theory of continental drift, now confirmed by the mechanism
of plate tectonics, has had a revolutionary impact on
explaining the evolutionary patterns of life on Earth.
Oceans can form or widen because new ocean floor crust
forms along the fracture (a mid-ocean ridge) where crustal
plates separate. Underwater volcanic eruptions exude new
plate material along the mid-ocean ridge. As a result, the
youngest crust material is right next to the mid-ocean ridge,
and the oldest material is furthest from the ridge. Geologists
can determine the actual ages of volcanic rocks by radioactivity
(see radiometric dating) and the relative ages of rocks
by determining the orientation of the magnetic fields of the
rocks (see paleomagnetism). Both the ages, and the magnetic
field patterns, of the rocks of the Atlantic Ocean floor
form bands of increasing age away from the Mid-Atlantic
Ridge. When geologists Drummond Matthews and Fred Vine