The notion of ever more old people needing ever more young people, who will in turn grow old and need even more young people, and so on ad infinitum, is an obvious ecological Ponzi scheme.

The fact is that no species has ever had such wholesale control over everything on earth, living or dead, as we now have. That lays upon us, whether we like it or not, an awesome responsibility. In our hands now lies not only our own future, but that of all other living creatures with whom we share the earth.

You can cry about death and very properly so, your own as well as anybody else's. But it's inevitable, so you'd better grapple with it and cope and be aware that not only is it inevitable, but it has always been inevitable, if you see what I mean.

Clearly we could devastate the world... as far as we know, the Earth is the only place in the universe where there is life. Its continued survival now rests in our hands

Terrorism is an immediate problem that people are very concerned about, and I am as concerned about that as anyone else. But it isn't an either or situation.

What humans do over the next 50 years will determine the fate of all life on the planet.

I often get letters, quite frequently, from people who say how they like the programmes a lot, but I never give credit to the almighty power that created nature.