Species Divergence
Based on comparisons between mtDNA of the dusky seaside sparrow and its close relative, Scott's seaside sparrow, John Avise and William Nelson were able to estimate the last time that the dusky sparrow and the seaside sparrow came in contact. Since it has been established that the dusky sparrow had a very small locale which it inhabits, it was isolated from other sparrows for a very long time. Assuming that the mtDNA in sparrows evolves at the rate which is estimated for mammals and other birds (approximately 2-4% every million years), then the last time the dusky sparrow was in contact with Scott's seaside sparrow was approximately 250,000-500,000 years ago, giving plenty of time for the dusky sparrow to establish differences between other varieties of species, such as its unique plumage and call.
Read more about this topic: Dusky Seaside Sparrow
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“Not only does every animal live at the expense of some other animal or plant, but the very plants are at war.... The individuals of a species are like the crew of a foundered ship, and none but good swimmers have a chance of reaching the land.”
—Thomas Henry Huxley (1825–95)