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.such as,if there is a snack with normal venom,another snack has overwhelming venom.but the habitat they live are full with some strong prey who need to be kill by the powerful venom.then,the snack with overwhelming venom will be survive.as the result,the average venom intensity will be increase.
stabilizing selection
when individuals near the center of the curve havee higher fitness than individuals at either end of the curve,stabilizing selection takes place.for example,if there are two extremely lizards,one isyellow,and the other is purple.however,the nomarl lizards should be green.the yellow lizard's struggle is its color will make it die easier in its environment,and the purple one' color causes it can not hide itself perfectly.therefore,the amout of yellow and purple will decrese while the green one will have more offfspring.
disruptive selection
when individuals at the upper and the lower ends of the cureve have higher fitness than individuals near the middle,disruptive selection takes place.here it is,if there are three kind of horse,the first is small,the second is normal,and the third one is big.when they face a lion at the same time,the small one can run away very fast,the big one can threat the lion and make it afraid to attack,while the normal can do nothing.because of that,the population of the small and big one will raise,but the normal size will be decline.
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