Blackwell Publishing

The evidence for evolution - How can evolution be observed?


This example contradicts species fixity

The variation in North American house sparrows has all evolved since 1852, when their common ancestors lived, all looking much like this sparrow opposite; the variation has taken a period of about 100 generations or less. The modern array of forms is all classified within one species; but the example shows how a noticeable amount of change can occur within the relatively short time that humans have been making observations.

The variation we see now must have arisen by change within populations through time; the spread of the population across North America was observable, and it can hardly be argued that each population, with its distinct size and color pattern, was separately created.

Because the house sparrows have not reached the stage of evolving new species, the example does not distinguish between transformism and evolution but it does contradict species fixity.

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