Encyclopedia of Evolution.pdf - Online Reading Center

of some H. erectus. This suggests that there was some evolutionary
advantage to the decrease in brain size. Nobody has a
clue as to what this might have been.
Other possibilities remain. Might the Flores Island hominins
have been descendants not of Java man but of earlier
hominin species such as H. habilis, or even australopithecines?
This is unlikely, since Flores Island is thousands of
miles away from the only places in which H. habilis and australopithecines
are known to have lived, and there is no evidence
that these earlier hominin species knew how to make
rafts. It is always possible that the small-brained skull came
from a pathological individual. Evidence against this interpretation
included the following: First, there are no recognizable
deformities in the skull that would suggest microcephaly,
other than the small size of the brain itself. Anthropologist
Dean Falk explains that even though the brain of H. floresiensis
was small, it had some structural characteristics that
resemble the normal brains of larger-brained hominins, rather
than those of microcephalics. Second, the individual lived
enough years to wear down his or her teeth and was smart
enough to make fire and tools. Third, how likely is it that the
very first skull one happens to find would be of a deformed
individual? Indonesian anthropologist Teuku Jacob insists
that the Flores Island people were not deformed but were
merely dwarf modern humans. But why would there have
been a whole population that consisted only of dwarves?
Another surprise was that the archaeological deposits
associated with the Flores Island hominins were produced as
recently as 18,000 years ago. The hominins might have persisted
even longer than this. Modern humans were certainly
in Indonesia by that time and may have caught a glimpse of
them. Every culture has legends about little people. Indonesian
legend describes “Ebu Gogo” little people. Indonesian
little-people legends might have had a basis in fact. The only
thing of which scientists are certain is that this species no longer
exists on the small and very well explored Flores Island.
Human evolution has produced the biggest brains relative
to body size, and among the biggest brains in absolute
size, that the world has ever known. However, the Flores
Island hominins demonstrate that human evolution can proceed
in the other direction, if conditions permit—a vision that
science fiction writer Herbert George Wells developed when
he invented the Eloi in his novella The Time Machine in the
early 20th century.
Further Reading
Brown, Peter, et al. “A new small-bodied hominin from the Late
Pleistocene of Flores, Indonesia.” Nature 431 (2004): 1,055–
1,061.
Culotta, Elizabeth. “Battle erupts over the ‘hobbit’ bones.” Science
307 (2005): 1,179.
Diamond, Jared. “The astonishing micropygmies.” Science 306
(2004): 2,047–2,048.
Falk, Dean, et al. “The brain of LB1, Homo floresiensis.” Science
308 (2005): 242–245.
Morwood, Michael, et al. “Archaeology and age of a new hominin
from Flores in eastern Indonesia.” Nature 431 (2004): 1,087–
1,091.
fossils and fossilization
———. “The people time forgot.” National Geographic, April 2005,
2–15.
Wong, Kate. “The littlest human.” Scientific American, February
2005, 56–65.
fossils and fossilization Fossils are the physical evidence
of organisms that have been dead for many years, past the
normal duration of decomposition; fossilization is the set of
processes by which they are formed. When volcanic or other
rocks erode, water carries sediment to the continental shelves
at the edges of the oceans, where it accumulates in layers
called strata. This process is occurring right now. As silt and
mud layers are buried, the increased temperature and pressure
transforms them into sedimentary rocks. The layers in
sedimentary rocks are visually distinguishable. Clay particles
become shale, while sand particles become sandstone. Fossils
are usually found in sedimentary rocks, since dead plants
and animals are often buried within the sediment. Intense
heat and pressure can transform volcanic or sedimentary
rocks into metamorphic rocks, in which the fossils are usually
destroyed. Fossils are not always destroyed by metamorphosis.
Structures that may be fossilized cyanobacteria can be
seen in the 3.5 billion-year-old Apex chert of Australia (see
origin of life).
Fossils have been known for millennia; but until the last
three centuries, most people thought fossils were simply peculiar
rocks that just happened to look like plants and animals,
rather than being the remains of actual plants and animals.
Leonardo da Vinci was one of the earliest scholars to recognize
fossils for what they really were, and he puzzled about why
fossils of seashells were found at the tops of mountains. His
solution to the problem reflected more of the medieval than
the modern mind. He conceived of the Earth as an organism,
therefore it must have a circulatory system, which means that
ocean water must circulate underground to the tops of mountains,
where it comes out as creeks and rivers—and sometimes
brings seashells with it. He was right about the fossils, though
wrong about how they got there. Another early scholar to recognize
fossils as remnants of formerly living organisms was
Danish geologist Niels Stensen (Nicholas Steno).
When an organism dies, it almost always decays. Under
some circumstances, decomposition is delayed, such as in the
presence of water and the absence of oxygen. As the organism
decays slowly, the space inside its body, sometimes even
inside of its cells, is filled with mineral deposits from the
water (see figure on page 166). The fossil may be completely
mineralized; alternatively, permineralization occurs when
minerals enter the dead organism without completely replacing
the original molecules. Under conditions of high temperature
and pressure, the sediments surrounding the organism
and the organism itself are both transformed into rock.
Because of chemical differences between the fossil and its surrounding
matrix, fossils usually stand out and may cause a
zone of weakness in the rock that contains them. Fossils are
therefore frequently found by geologists who strike the rocks
with hammers; the fracture reveals the fossils. Mineral deposits
inside of a coal seam (coal balls), rather than the coal itself,
often contain fossils of the plants from which the coal was