Quotes About Life prolongation

Why are they so stupid?' asked Human. 'Not to know the truth when they hear it?' 'They aren't stupid,' said the Speaker. 'This is how humans are: We question all our beliefs, except for the ones that we really believe, and those we never think to question. They never thought to question the idea that the original Speaker for the Dead died three thousand years ago, even though they know how star travel prolongs life.

What is "rational" consists in prolonging life, avoiding pain, satisfying the appetite for hunger and sex. Only some such definition sheds any light on the discourse of the last centuries.