Encyclopedia of Evolution.pdf - Online Reading Center

as deposits of a single gigantic flood, as has been claimed by
creationists (see creationism).
Further Reading
Eldredge, Niles. “Evolution of the Earth.” Chap. 4 in The Pattern of
Evolution. New York: Freeman, 1999.
Murphy, J. Brendan, and R. Damian Nance. “How do supercontinents
collide?” American Scientist 92 (2004): 324–333.
convergence Convergence occurs when similar adaptations
evolve in separate lineages of organisms. Convergent adaptations
have evolved separately (by convergent evolution),
rather than being inherited from a common ancestor. Convergence
can often be recognized because the organisms evolve
the adaptation in different ways. This has been experimentally
demonstrated in bacteria. Scientists grew some populations
of the gut bacterium Escherichia coli in the absence of
the sugar maltose, and the bacteria lost the genes that would
allow them to use maltose as a food source. Then they were
exposed to maltose again. The populations produced bacteria
that had mutations that allowed them to metabolize the
maltose. Each of these populations evolved a different set of
mutations. The reinvention of the ability to use maltose was
a convergence in the separate bacterial populations; but each
population achieved this result in a different way.
The following are just a few of the many thousands of
possible examples, from plants and from animals.
Plant Convergences
Plant adaptations to climatic conditions. Plants have evolved
convergent adaptations to stressful environmental conditions.
convergence
• Bushes that live in dry climates have small leaves. Small
leaves dissipate heat into the air more efficiently than large
leaves, which is important in hot, dry climates where plants
must restrict the amount of water that they use in evaporative
cooling. Small-leaved bushes have evolved within many
different plant families, all of which have species with larger
leaves. Small leaves are therefore a new adaptation in
many different plant families. In some environments, these
bushes are also adapted to sprouting or seed germination
after periodic fires. Habitats that are dominated by bushes
with small leaves, and that experience periodic fires, have
evolved separately in California (chaparral), Chile (matorral),
France (maquis and garrigue), Australia (mallee), and
South Africa (fynbos).
• The succulent growth form, which allows water storage
and CAM (see photosynthesis, evolution of), has
evolved in several plant families, for example the cactus
and lily families in North American deserts and the spurge
family in South African deserts.
• The C 4 form of photosynthesis may have evolved more
than 30 different times.
• Several lineages of plants have evolved the ability to grow
in soil that is toxic due to high concentrations of heavy
metal ions.
Plant adaptations to pollination methods. Plants have evolved
convergent adaptations to the same pollination mechanisms.
• Flowers that attract hummingbirds as pollinators are usually
tubular and red. The tubular red form of flower has
evolved in many different plant families. In one instance, a
single mutation began the process that changed the yellow,