Being a man has always been dangerous. 阅读理解有几处不明白

Being a man has always been dangerous. There are about 105 males born for every 100 females, but this ratio drops to near balance at the age of maturity, and among 70-year-olds there are twice as many women as men. But the great universal of male mortality is being changed. Now, boy babies survive almost as well as girls do. This means that, for the first time, there will be an excess of boys in those crucial years when they are searching for a mate. More important, another chance for natural selection has been removed. Fifty years ago, the chance of a baby (particularly a boy baby) surviving depended on its weight. A kilogram too light or too heavy meant almost certain death. Today it makes almost no difference. Since much of the variation is due to genes, one more agent of evolution has gone.
第一句话为什么是being a man，to be a man或be a man可以吗？
But the great universal of male mortality is being changed.最后变成is changing行吗？
when they are searching for a mate，为什么用进行时？
one more agent of evolution has gone。这句是什么意思？怎么还有个more啊？gone的是指的是前面讲的体重原因吗？

being a man 是动名词作主语的用法。而to be a man 则成了“要成为一个男人”的意思，因为不定式表一次性的动作。
第二个问题在于mortality这一名词和change 之间是被动关系，不能用主动形式。
第三个问题主句所表状态是和从句中寻找这一动作是同时发生的。
one more又一个进化的原动力消失了。

BEING 是动词作主语，，要用进行时 IS BEING CHANGED 是被动的进行时，，，IS CHANGING 是主动的进行时，不一样 WHEN 表示当，，当上下文是一般式时用进行时

第一个问题 动名词作主语 和不定式作主语的区别 动名词 经常性 习惯性 一般泛指性 不定式 阶段性 特定性 将来性 具体性 如 teaching english is his job. to teach english is his job today. 第二个问题 change 在这里是及物动词 和主语是被动关系 所以用被动语态。不能变。 第三个问题 因为这里when表示的是时间段 表示动作持续的时间段 和主句的状态一致 第四个问题 more 是另外的 又 的意思 one more 是又一个的意思 gone的主语 是agent. 指的是主张进化的观点

此句中没有宾语 只有表语dangerous being a man 是主语 has been 是谓语