A billion could live off the earth; 6 billion living as we do is far too many, and you run out of planet in no time.

Humans on the Earth behave in some ways like a pathogenic micro-organism, or like the cells of a tumor.

Imagine a survivor of a failed civilization with only a tattered book on aromatherapy for guidance in arresting a cholera epidemic. Yet, such a book would more likely be found amid the debris than a comprehensible medical text.

The entire range of living matter on Earth from whales to viruses and from oaks to algae could be regarded as constituting a single living entity capable of maintaining the Earth's atmosphere to suit its overall needs and endowed with faculties and powers far beyond those of its constituent parts.

Those who fail to see that population growth and climate change are two sides of the same coin are either ignorant or hiding from the truth. These two huge environmental problems are inseparable and to discuss one while ignoring the other is irrational.

If it hadn't been for the Cold War, neither Russia nor America would have been sending people into space.

I'm not religious, but I put it that way because I feel so strongly. It's the one thing you do not ever do. You've got to have standards.