Encyclopedia of Evolution.pdf - Online Reading Center

uses a mutant form of lysozyme to digest the bacteria. This
adaptation has evolved separately in cows, langur monkeys,
and hoatzin birds.
In many cases, convergent evolution does not require a total
reinvention of an adaptation.
• Limonene has evolved separately in several lineages of
plants (see above), but most flowering plants have terpene
synthases, the enzymes that produce the immediate chemical
precursors of limonene.
• Ornithologist N. I. Mundy explains that the evolution of
similar color patterns in separate bird lineages has resulted
from the modification of an underlying genetic pattern that
they inherited from their common ancestor.
• Eyes have evolved perhaps 40 separate times in the evolutionary
history of animals (see above). All of these animals
share an organizer gene, called pax, that stimulates the
development of eyes. In each of these lineages, the actual
structure of the eye has evolved separately. There is a
marine worm that has compound eyes, like those of other
invertebrates, but also has brain lobes that have photosensitive
chemicals similar to those of vertebrate eyes. Apparently
vertebrate eyes evolved from invertebrate brain lobes
rather than from invertebrate eyes.
In modern organisms, scientists can recognize convergence,
because despite the external similarities, the organisms
are internally different and have achieved the convergence in
different ways. In looking at fossils, scientists cannot always
tell whether organisms shared a characteristic because they
inherited it from a common ancestor, or because they evolved
it separately by convergence. This sometimes makes reconstructing
fossil history difficult. Sometimes in the fossil record
a species appears to have become extinct then reappears. Is it
because the species was rare for a long time, then reappeared
in greater abundance (what paleontologist David Jablonski
calls Lazarus taxa, because they appeared to rise from the
dead), or because another lineage evolved similar features
by convergence, and it just looked like a reappearance (what
paleontologist Douglas Erwin calls Elvis taxa)?
Every evolutionary scientist understands that there are
many examples of convergent evolution. They differ in how
much importance they give convergence in the overall pattern
of the evolution of life. Some evolutionary scientists claim
that evolution has so many different possible directions that
the actual course taken by evolution is a matter of historical
contingency, a viewpoint expressed by evolutionary biologist
Stephen Jay Gould (see Gould, Stephen Jay; progress,
concept of). Gould said that evolution produced a bush of
different forms, not a ladder leading upward to human perfection.
These scientists consider convergence to be details
that have occurred at the tips of the branches of the bush of
life. Others, like paleontologist Simon Conway Morris, insist
that convergence is so frequent that it constitutes one of the
major features of evolution. They point out that even though
there may be an almost infinite number of possible biological
adaptations, there are only a limited number of strategies
that work, and evolution keeps finding these strategies over
Copernicus, Nicolaus
and over. Conway Morris agrees with Gould that evolution
is a bush, not a ladder; but in this bush, he says, many of the
branches are parallel. Conway Morris cites the parallel evolution
of large brains in cetaceans (such as dolphins) and in
humans. In the human lineage, there was a separate increase
in brain size in the lineage that led to Homo sapiens, the lineage
that led to Neandertals, perhaps also in the lineages
that led to Asian Homo erectus; and in the robust australopithecines.
Agriculture and civilization in humans evolved
separately in East Asia, the Middle East, and America. Intelligence
does not always offer an evolutionary advantage (see
intelligence, evolution of), but when it does, one would
expect that the large processing center for the nerves would
be near the front end of the animal, where most of the sensory
organs are located (a big brain in a head with eyes and nose).
Conway Morris says that the evolution of intelligence is a rare
event, but that if humans encounter an intelligent life-form
somewhere else in the universe it would probably be something
that they would recognize as a person, perhaps even as a
human. This is why he refers to “inevitable humans in a lonely
universe” (see essay, “Are Humans Alone in the Universe?”).
Further Reading
Conway Morris, Simon. Life’s Solution: Inevitable Humans in a
Lonely Universe. Cambridge University Press, 2003.
Mundy, N. I., et al. “Conserved genetic basis of a quantitative plumage
trait involved in mate choice.” Science 303 (2004): 1,870–1,873.
Summarized by Hoekstra, Hopi E., and Trevor Price. “Parallel evolution
is in the genes.” Science 303 (2004): 1,779–1,781.
Patterson, Thomas B., and Thomas J. Givnish. “Geographic cohesion,
chromosomal evolution, parallel adaptive radiations, and consequent
floral adaptations in Calochortus (Calochortaceae): Evidence
from a cpDNA phylogeny.” New Phytologist 161 (2003): 253–264.
Pichersky, Eran. “Plant scents.” American Scientist 92 (2004): 514–
521.
Shadwick, Robert E. “How tunas and lamnid sharks swim: An evolutionary
convergence.” American Scientist 93 (2005): 524–531.
Weinrech, Daniel M., et al. “Darwinian evolution can follow only
very few mutational paths to fitter proteins.” Science 312 (2006):
111–114.
Copernicus, Nicolaus (1473–1543) Polish Astronomer
Mikołaj Koppernigk (who Latinized his name to Nicolaus
Copernicus) was born February 19, 1473. He attended university
in Krakow, Poland, and appeared to be headed for
a church career. But he also studied astronomy, geography,
and mathematics and was particularly interested in planetary
theory and patterns of eclipses. He was offered a church
administrative position but delayed taking it so that he could
continue scientific studies in astronomy and medicine, which
he undertook in Italy. He then returned to Poland and continued
studying astronomy while he performed church duties.
At the time, astronomers considered the Earth to be the
center of the universe. The Sun and the planets circled the
Earth. This belief made it difficult to explain the apparent
movements of the planets in the sky, especially when the planets
appeared to reverse their motion temporarily. Astronomers