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Because humans can shape their environment, they are not subject to pressures of natural
selection in the same way as other organisms. While they may adapt and evolve,
evolution will probably happen more slowly. For example, humans with very fair skin
can now live in very hot, sunny environments: shelter, clothing, and sunscreen all help to
protect their skin from the sun, so that they will have as much reproductive success as
people with darker skin who are naturally adapted to such environments.
Convergent evolution is when two species develop the same traits or features
independently, even though their last common ancestor did not have this trait. An
example of convergent evolution would be the opposable thumb of opossums, which is
also found in primates but not in common ancestors. Divergent evolution is when a single
species diverges to form two or more related species due to evolutionary pressures that
cause different features to develop, or when two related species become more and more
dissimilar. An example of this would be the red fox and the kit fox. The kit fox is adapted
for a desert environment, with a sandy color for camouflage and large ears to dissipate
heat. The red fox’s color helps it to blend in with trees and dirt.
Adaptive radiation happens when a species colonizes a new area with many
unfilled niches. The species quickly adapts to form many subspecies with different traits
that allow the species to survive across many areas of the ecosystem. For example, in
Lake Victoria, a very deep lake in Central Africa, cichlids evolved from one species to
300 in about 15,000 years (“Adaptive radiation”, n.d.).
Co-evolution is the change in one species in response to a change in another. For
example, the garter snake, a predator, has evolved a resistance to nerve toxins that the
Rough-skinned newt (Taricha granulosa) produces in its skin. The newt, in response, has
adapted more and more toxic poisons (“Co-evolution”, n.d.).
An impact of adaptive radiation for future humans is that human destruction of
species and environments may open up new niches, or introduce species to ecosystems
they did not previously occupy. Previously non-invasive species may adapt to become
invasive and may over time become as damaging as current invasive species such as
kudzu and fire ants. For example, in Hawaii, there is a crisis of invasive species, and
Hawaii, as an island chain, is the perfect environment for adaptive radiation to take place.
As the invasive species crowd out native species, niches will be left unfilled (Loope &
Canfield, 2000). The invasive species may then adapt to fill the niches even more
Adaptive radiation. (n.d.). Retrieved December 13, 2008, from Wikipedia:
Co-evolution. (n.d.). Retrieved December 13, 2008, from Wikipedia:
Loope, L. & J. Canfield. (2000, July/August). Hawaii: A model for addressing invasive
species. People, Land, & Water. Retrieved December 13, 2008, from