When permitted to listen to alternative opinions and engage in substantive debate, people have been known to change their minds. It can happen.

In more than one respect, the exploring of the Solar System and homesteading other worlds constitutes the beginning, much more than the end, of history.

When you make the finding yourself - even if you're the last person on Earth to see the light - you'll never forget it.

The secrets of evolution are death and time-the deaths of enormous numbers of lifeforms that were imperfectly adapted to the environment; and time for a long succession of small mutations.

Humans — who enslave, castrate, experiment on, and fillet other animals — have had an understandable penchant for pretending animals do not feel pain. A sharp distinction between humans and 'animals' is essential if we are to bend them to our will, make them work for us, wear them, eat them — without any disquieting tinges of guilt or regret. It is unseemly of us, who often behave so unfeelingly toward other animals, to contend that only humans can suffer. The behavior of other animals renders such pretensions specious. They are just too much like us.

We began as wanderers, and we are wanderers still.

The simplest thought, like the concept of the number one, has an elaborate logical underpinning.