Macroevolution: Races and Race Formation

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Cline: Gradual changes in the phenotype along an environmental gradient.

Differentiation in stature (sizes in cm) among yarrowplant populations (Achillea lanulosa) in the Sierra Nevada, California.

Cline in human skin color

An example of a stepcline. Changes between forms occur abruptly, without any obvious environmental change.

Race: Groups of populations with similar allele frequencies that are different from other related populations.

Genetic variation within and among human races. Notice that although phenotypic differences among races seem to be pronounced, the underlying genetic differences are very minor. Perhaps, our sensory systems are fine tuned to detect even very slight differences in our own species.

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