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Stabilising selection 稳定化选择

Initially there is a wide range of fur length about the mean of 1.5cm.

最初，毛皮长度的范围很广，平均为1.5厘米。

Due to rapid breeding in either very cold or very warm weather, animals with extreme fur lengths survive.

由于在非常寒冷或非常温暖的天气中快速繁殖，具有极端毛发长度的动物得以生存。

When the temperature remains constant with little variation, the individuals with very short or very long hair become less numerous and are eventually eliminated from the population.

当温度保持不变，变化不大时，毛发很短或很长的个体数量就会减少，并最终从种群中被淘汰。

Directional selection 方向性选择

If the temperature falls, the individuals with longer fur length are at an advantage as they have better insulation against the cold.

如果气温下降，毛发较长的个体处于优势地位，因为它们有更好的绝缘性能来抵御寒冷。

There is a selection pressure favouring the animals with longer fur so these animals are more likely to survive and thus reproduce.

有一种有利于长毛的动物的选择压力，所以这些动物更有可能生存下来，从而进行繁殖。

Over several generations, the average fur length increases as more young have inherited the genes for long fur. When the mean fur length has reached the most advantageous length, the selection pressure ceases.

经过几代人的努力，平均毛皮长度增加，因为更多的年轻人继承了长毛皮的基因。当平均毛皮长度达到最有利的长度时，选择压力就停止了。

Disruptive selection 破坏性选择

If the temperature difference between summer and winter increases, long hair for animals being active during the winter or short hair for animals being active during the summer is advantageous.

如果夏季和冬季的温差增大，在冬季活动的动物的长毛或在夏季活动的动物的短毛是有利的。

Intermediate fur length is disadvantageous. Therefore, two sub populations are formed over time.

中间的毛发长度是不利的。因此，随着时间的推移，会形成两个亚种群。

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