When individuals at one end of the curve have higher fitness than individuals in the middle or at the other end, directional selection takes place. The range of the phenotypes shifts as some individuals fail to survive and reproduce while others succeed. An example of a directional selection is when a population of seed-eating birds experiences directional selection when a food storage causes the supply of small seeds to run low. When individuals near the center of the curve have higher fitness than individuals at either end of the curve, stabilizing selection takes place. This situation keeps the center of the curve at its current position, but it narrows the overall graph. An example of a stabilizing selection is when a human babies that is born at an average mass, it is more likely to survive than the ones that are born either smaller or the ones that are born much larger than average. When individuals at the upper and lower ends of the curve have higher fitness than individuals near the middle, disruptive selection takes place. In such situations, selection acts most strongly against individuals of an intermediate type. An example of a disruptive selection is when an average-sized seeds become less common, and the ones that are larger or smaller seeds becomes more common.
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