It's been proven by quite a few studies that plants are good for our psychological development. If you green an area, the rate of crime goes down. Torture victims begin to recover when they spend time outside in a garden with flowers. So we need them, in some deep psychological sense, which I don't suppose anybody really understands yet.

I see that within each human being there are two extremes: there's the loving, the passionate, altruistic side that has evolved with us, and then there's the violent, brutal side that has evolved with us. The question for each individual is: which side is going to come out on top?

In Tanzania, the chimps are isolated in a very tiny patch of forest. I flew over it 13 years ago and realized that, basically, all the trees had gone, that people all around the park are struggling to survive. It became very clear that there was no way to protect the chimps while the people were in this dire circumstance.

We have to create more and more vegetarians, and help people to understand that it is not only the suffering of the animals (which is what made me vegetarian) but also the incredible harm to the environment, the tremendous amount of greenhouse gas created by the whole vast machinery of intensive animal farming.

Language allows us to talk about the past and plan the future. We can teach children about things that are not present. And above all, we can bring people with different backgrounds and different knowledge together to discuss our problems. This actually gives me hope. I still think we are smart enough to not destroy planet Earth, our only home.

We can't leave people in abject poverty, so we need to raise the standard of living for 80% of the world's people, while bringing it down considerably for the 20% who are destroying our natural resources.

Cultural speciation had been crippling to human moral and spiritual growth. It had hindered freedom of thought, limited our thinking, imprisoned us in the cultures into which we had been born. . . . These cultural mind prisons. . . . Cultural speciation was clearly a barrier to world peace. So long as we continued to attach more importance to our own narrow group membership than to the ‘global village’ we would propagate prejudice and ignorance.