My work at MIT had focused on what we could build in space once we had inexpensive space transportation and industrial facilities in orbit. And this led to various sorts of work in space development.

In a sense, artificial intelligence will be the ultimate tool because it will help us build all possible tools.

Plants with leaves no more efficient than today's solar cells could out-compete real plants, crowding the biosphere with an inedible foliage. Tough omnivorous bacteria could out-compete real bacteria: They could spread like blowing pollen, replicate swiftly, and reduce the biosphere to dust in a matter of days. Dangerous replicators could easily be too tough, small, and rapidly spreading to stop - at least if we make no preparation. We have trouble enough controlling viruses and fruit flies.

If you take all the factories in the world today, they could make all the parts necessary to build more factories like themselves. So, in a sense, we have a self-replicating industrial system today, but it would take a tremendous effort to copy what we already have.

Likewise nanotechnology will, once it gets under way, depend on the tools we have then and our ability to use them, and not on the steps that got us there.

Today we have big, crude instruments guided by intelligent surgeons, and we have little, stupid molecules of drugs that get dumped into the body, diffuse around and interfere with things as best they can. At present, medicine is unable to heal anything.

I had been impressed by the fact that biological systems were based on molecular machines and that we were learning to design and build these sorts of things.