Encyclopedia of Evolution.pdf - Online Reading Center

migrated into Europe and displaced the Neandertals during
the interglacial period. The Neandertals were extinct by
the time the most recent glaciation reached its maximum.
Some anthropologists consider not just the genus Homo
but the modern species H. sapiens to be children of the Ice
Age, because the glacial advances forced previously scattered
tribes to come in contact in southern Europe. This is the
period of the great Cro-Magnon cave paintings of southern
Europe.
Further Reading
Bonnicksen, Thomas M. “The Great Cold.” Chap. 1 in America’s
Ancient Forests: From the Ice Age to the Age of Discovery. New
York: John Wiley, 2000.
Broecker, Wallace S. “Was the Younger Dryas triggered by a flood?”
Science 312 (2006): 1,146–1,147.
Gould, Stephen Jay. “The freezing of Noah.” Chap. 7 in The Flamingo’s
Smile: Reflections in Natural History. New York: Norton, 1985.
———. “The great Scablands debate.” Chap. 19 in The Panda’s
Thumb: More Reflections in Natural History. New York: Norton,
1980.
Macdougall, Doug. Frozen Earth: The Once and Future Story of Ice
Ages. Berkeley: University of California Press, 2004.
Petit, Rémy J., et al. “Hybridization as a mechanism of invasion in
oaks.” New Phytologist 161 (2003): 151–164.
Pielou, E. C. After the Ice Age: The Return of Life to Glaciated
North America. Chicago: University of Chicago Press, 1992.
Raymo, Maureen E., L. E. Lisiecki, and Kerim H. Nisancioglu. “Pliopleistocene
ice volume, Antarctic climate, and the global δ 18 O
record.” Science 313 (2006): 492-495.
Scher, Howie D., and Ellen E. Martin. “Timing and climatic consequences
of the opening of Drake Passage.” Science 312 (2006):
428–430.
Stanley, Steven M. Children of the Ice Age: How a Global Catastrophe
Allowed Humans to Evolve. New York: Harmony Books, 1996.
inbreeding depression See Mendelian genetics.
inclusive fitness See altruism.
Inherit the Wind See Scopes Trial.
instinct See behavior, evolution of.
intelligence, evolution of Intelligence is highly overrated.
Most species do not have very much of it. Eighty percent
of animal species are arthropods (see invertebrates,
evolution of), which do not have high levels of intelligence
and show no evolutionary trend toward increasing it.
High levels of intelligence evolved in the few species that do
have it as a result of special circumstances that are still not
understood.
Intelligence has proven impossible to define in a manner
that all scientists can accept. If intelligence requires only a
coordinated response to complex environmental factors, then
plants have intelligence, as explained in the article by biologist
Anthony Trewavas. Most scientists restrict the concept of
intelligence to animals, which have nervous systems. Human
intelligence, evolution of 0
intelligence includes consciousness, self-awareness, and the
ability to form abstract concepts. Evolutionary scientists recognize
a whole range of levels of animal intelligence.
There are evolutionary reasons why intelligence has
evolved only in animals. Microbes and protists (see archaebacteria;
bacteria, evolution of; eukaryotes, evolution
of) could not have evolved intelligence, since they are
primarily single-celled. Plants and fungi could not evolve
intelligence, which requires a nervous system for the acquisition,
processing, and storage of information.
In some groups of animals, such as the arthropods,
a large body size and therefore a brain as large as that of a
human is unlikely to evolve. But in many other animal lineages,
intelligence could have evolved if it had provided a
significant fitness advantage (see natural selection). The
fact that high levels of intelligence have evolved so seldom
during the history of animal life on Earth suggests that the
circumstances that favor intelligence are rare. Therefore, as
evolutionary biologist Stephen Jay Gould (see Gould, Stephen
Jay) pointed out, if complex life were to evolve all over
again, it is unlikely that a human level of intelligence would
evolve. Furthermore, science fiction notwithstanding, scientists
should not expect to find highly intelligent life on every
planet that is capable of supporting complex life. Gould
strongly rejected the idea that structurally simpler organisms
are evolving toward higher intelligence (see progress, concept
of).
High levels of intelligence require big brains, and big
brains are very expensive. The human brain consumes a tremendous
share of the food and oxygen that is available in
the blood. Humans have an encephalization quotient, which
compares human brain size with that of an average mammal
of the same size, of about 6. The encephalization quotient of
humans compared to other primates is about 3 (see allometry).
Big brains, and high intelligence, are simply not worth
the cost for most animal species.
Biologists use the encephalization quotient rather than
absolute brain size to compare animal species because brain
size is correlated with body size. Big animals require bigger
brains because their larger bodies have more sensory information
to process (particularly the internal sensory information
that informs the brain what is happening inside the body) and
more muscles to control. In fact, beyond a certain size limit,
centralized nervous control of a body may be biologically
impossible. The largest dinosaurs appear to have had a somewhat
large brain in their heads, that processed information
to and from the front end, and a smaller swelling of the spinal
cord near their tails, which processed information to and
from the rear end. Nerve transmissions are rapid (particularly
in nerve cells, or gray matter, that have fatty sheaths, or white
matter) but apparently not rapid enough for the head end of
the dinosaur to take full control of the entire body.
Intelligence is not perfectly correlated with brain size.
Within the size range of the modern human brain, from about
80 to over 120 cubic inches (1,200 to 2,000 cc), there appears
to be no correlation between brain size and intelligence. Men
have larger brains than women, on the average, but are also
larger than women. Even when differences of body size are