难句解析：
①There 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.
▲该句是由三个递进关系的简单句组成的并列句，句法结构比较清晰。
△第一个分句的关键词在born，表明该比数是婴儿出生时的性别比例；第二个分句的关键词在near balance（接近持平）和at the age of maturity，表示性别比例的持平状态发生在成年时期；第三个分句的70-year-olds指代的是“70岁的人们”，作名词。
②Again, differences between people and the opportunity for natural selection to take advantage of it have diminished.
▲注意differences between people和the opportunity for natural selection to take advantage of it是两个并列的主语，千万不要理解成people与the opportunity是between的并列宾语。
△and连接的两个并列部分是differences between people和the opportunity for natural selection to take advantage of it，而不是people和the opportunity。另外注意句中的it指代的是differences between people。
③The grand mediocrity of today — everyone being the same in survival and number of offspring — means that natural selection has lost 80％ of its power in upper-middle-class India compared to the tribes.
▲该句的主语是The grand mediocrity，谓语是means，其后跟着that引导的宾语从句that natural selection has lost 80％ of its power in upper-middle-class India compared to the tribes，其中compared to the tribes是分词结构作状语，省略了if/when being。破折号中间everyone being the same in survival and number of offspring是典型的插入语，其中survival和number of offspring都是介词in的宾语。
△grand在此处不是“宏伟，壮丽”的意思，而是“程度很深”；mediocrity也非“平庸，平常”，而是“平均化”或“折衷”；offspring是“后代”。另外要理解natural selection has lost 80％ of its power in upper-middle-class India的意思，这里是指在原来的社会不平等的情况下，印度中上层阶级拥有一些能使自己在自然选择中处于优势的特权，而随着医疗和卫生条件的改变，下层人民也拥有同样的生存条件，因此中上层阶级就丧失了80％的自然选择中的优势。
④Darwin had a phrase to describe those ignorant of evolution: they "look at an organic being as a savage looks at a ship, as at something wholly beyond his comprehension."
▲冒号后的句子是主句中a phrase的同位语。该同位语从句中的结构是A does something as B does something（A做某事的样子正像B做某事的样子）。
△those ignorant of evolution指对生物进化过程一无所知的人，其后的they也指代这些人。最后的his指代前面的a savage。beyond his comprehension超出了他的理解范围。
来源:可可英语 http://www.kekenet.com/kaoyan/201406/304431.shtml