The equal ratio of sexes is so common in nature, most people never wonder why it is that way.

雌雄个体数量平衡在自然界中非常常见，多数人从未惊奇为什么会这样。

The population would be in a constant see-saw towards one sex or the other until, finally, a mutation arises that results in an equal ratio of offspring.

人口将会像一个跷跷板一样，两端的分别是雌性和雄性，直到最后某种变异出现，导致雄雌数量平衡的局面产生。