Human beings have distinguished themselves from other animals, and in doing so ensured their survival, by the ability to observe and understand their environment and then either to adapt to that environment or to control and adapt it to their own needs.

　　These expenses , however, usually involve the rent of a small office , expenses for stationary, and possibly , the salary of a secretary.

　　He must assume that you have lived in the tropics , have never seen a coat worn or put on, and that he is to tell you verbally how to do it.

　　要点分析和参考译文

　　要点：此句为一个多层次的并列结构，“by” 以前的部分为句子的主体部分，由“and”连接的两个并列的分句组成。第二个分句的主语和一部分谓语省略了以避免重复。In doing so可以理解为in the process of distinguished themselves from other animals.第二个分局的完整句子应为and in doing so （they have） ensured their survival.By 所引导的短语里ability带了多个动词不定式做修饰，这些不定式又存在着一个并列的结构，to observe and （to） understand与either……or引导的to adapt to……，to control and （to） adapt it……得并列，and连接。
　　参考译文：人类已把自己和其他动物区别开了。人类具有观察和了解周围环境的能力，能适应环境，控制环境和根据自己的需要改造环境。人类就是这样生存了下来。

　　要点：在谓语动词involve 后面是由三个平行的名词短语构成的宾语：he rent of a small office , expenses for stationary, the salary of a secretary.副词however及possibly 为插入语。
　　参考译文：然而，这些费用通常包括租赁一间小小的办公室和办公用品的支出，或许还要包括秘书的工资。

　　要点：本句中, that 引导的宾语从句共有三个，have never seen……，是一个省去了引导词that及主语you的宾语从句；过去分词worn or put on作宾语coat的补语。
　　参考译文：他肯定以为，你一直居住在热带从来没有见过穿在身上的外衣或怎样穿外衣，故而他要告诉你如何穿外衣。