Thanks Linda,

Rather like the dandelion adapting short stems on mowed lawns. One more piece of evidence that evolution is occurring.
http://www.pnas.org/cgi/content/abstract/0708446105v1
http://en.wikipedia.org/wiki/Crepis

Rates of evolution are dependent on the opportunity and selection pressures in action at any time. Each mechanism could be a topic on it's own, but we can look at the broad picture first:

Observation (1): no two organisms are identical.

Observation (2): some of the differences are hereditary (genetic, genotype), some are due to environmental effects (affect development, phenotype), and some are acquired by the organisms (behavioral, learned, individual traits, memes).

Observation (3): some (not all) of the difference between organisms enable some (not all) of the organisms to survive and breed more than others.

Observation (4) to affect the population of organisms, traits need to be passed from one generation to the next. Genetic traits are passed by genes, environmental traits are passed by the environment, learned traits are passed by memes.

Conclusion (1): hereditary traits that result in differences that enable some organisms to survive and breed better, will become more common in following generations of those organisms than hereditary traits that don't, or that hinder survival and breeding, and evolution - the change in hereditary traits in populations from generation to generation - will occur.

Conclusion (2): traits due to environmental effects that result in differences that enable some organisms to survive and breed better, will become more common in following generations for those organisms that remain in that environment, compared to environmental traits that don't, or that hinder survival and breeding, and also compared to organisms that leave that environment (or the environment changes).

Conclusion (3): traits that are learned that result in differences that enable some organisms to survive and breed better, will become more common in following generations for those organisms that continue to teach them, compared to acquired traits that don't, or that hinder survival and breeding.

Conclusion (4): hereditary traits, environmental traits, and acquired traits, that don't affect survival or breeding can still spread within breeding populations.

Conclusion (5): isolated populations of originally similar organisms over time will become different from each other. After several generations they will have different distributions of genetic traits, different traits due to environmental factors and different learned behaviors.

Theory: this is sufficient to explain the diversity of life we see in the world today, in historical accounts, in the fossil record and in the genetic evidence.

Note that this is how science operates: take observations, develop conclusions from those observations, formulate a theory based on those conclusions, and then test the theory.

Enjoy.
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