But as the cerebellum degrades with age, so does the quality of memories. The memories are there, but they're not as good.

I've always loved airplanes and flight. The space program was really important to me as a kid. I still have a photo of Armstrong and Aldrin on the moon in my living room.

To leave the world better than you found it, sometimes you have to pick up other people's trash.

Burning carbon-based substances like oil, gas, and especially coal, produces billions of tons of extra carbon dioxide each year. Methane gas from cows and pigs and other animals on our large farms ends up in the atmosphere as well, trapping more of the sun's energy as heat.

For me, the meaning of life is pretty clear: Living things strive to pass their genes into the future.

History is but the record of the public and official acts of human beings. It is our object, therefore, to humanize our history and deal with people past and present; people who ate and possibly drank; people who were born, flourished and died; not grave tragedians, posing perpetually for their photographs.

Evolution is one of the most powerful and important ideas ever developed in the history of science. Every question it raises leads to new answers, new discoveries, and new smarter questions. The science of evolution is as expansive as nature itself. It is also the most meaningful creation story that humans have ever found.