23.15 Natural selection produces adaptations, such as those seen in polar bears that inhabit the extreme Arctic environment. These bears blend into the snowy background, which helps them in hunting seals. The hairs of their fur stay erect even when wet, and thick layers of blubber provide insulation, which protects against subzero temperatures. Their digestive tracts are adapted to a seal-based carnivorous diet. (Tom and Pat Leeson/DRK Photo.)

A1 A1 A1A2 A2A2 Selection coefficient (1 — W): sn = 0 s12 = .5 s22 = .8

We usually speak of selection for a particular genotype, but keep in mind that, when selection is for one genotype, selection is automatically against at least one other genotype.

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