Chlorine is a deadly poison gas employed on European battlefields in World War I. Sodium is a corrosive metal which burns upon contact with water. Together they make a placid and unpoisonous material, table salt. Why each of these substances has the properties it does is a subject called chemistry.

We go about our daily lives understanding almost nothing of the world.

Even today the most jaded city dweller can be unexpectedly moved upon encountering a clear night sky studded with thousands of twinkling stars. When it happens to me after all these years it still takes my breath away.

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.

You can get into a habit of thought in which you enjoy making fun of all those other people who don't see things as clearly as you do. We have to guard carefully against it.

There is a report that says that kids who watch violent TV programs tend to be more violent when they grow up. But did the TV cause the violence, or do violent children preferentially enjoy watching violent programs?

The beauty of a living thing is not the atoms that go into it, but the way those atoms are put together.