30年前笔者曾写过一本名为《不断扩大的圈》的书，书中写道，从历史角度看，被我们纳入道德考量的事物圈子一直在扩大，先是从部落到国家，接着是种族或是族群，再到全人类，最后延伸到非人类生物。
Thirty years ago, I wrote a book called The Expanding Circle, in which I asserted that, historically, the circle of beings to whom we extend moral consideration has widened, first from the tribe to the nation, then to the race or ethnic group, then to all human beings, and, finally, to non-human animals.