 I have no doubt that the fundamental source of all our problems, particularly our environmental problems, is population growth. I can't think of a single problem that wouldn't be easier to solve if there were less people. And the projections now are awesome. In the time when I've been making natural history programs, which of course doesn't seem very long to me, the population of the world has tripled, just in my lifetime, and less than my lifetime. And we all know about geometric growth. And that, if we are able, which of course we can't, if we're able to stem it, we might be able to have a better chance to grapple with the problems that we've got at the moment. But we can't. The best we can do is to slow down the rate of increase. We certainly can't stop it. I suppose the biggest impact on human health I've seen is slums. Slums in South America, slums in India, slums in Africa. Huge areas occupied by people living whole families in tiny little apartments with no sanitation and no future. The one source of comfort, and it's only a tiny thread, is that the knowledge that wherever you empower women, wherever they have the vote, wherever they ever had the education, wherever they have the free will and are in charge of their own lives and not dictated to by men, the birth rate falls, which is a very good reason for getting rid of slums, for increasing education and for dealing with all the other social problems that many people, many people have. And if there is a shaft of light there, but it's only a very thin shaft. Environmental change is not the same all over the world. Desertification is one particular problem. And there's a lot we can do about desertification. There's a lot we can deal in agricultural terms and special terms as to how we deal with it. The production of power, we must be able to solve the problem of solar power in a sensible way. I mean, we're getting better all the time. But the notion that all this power is pouring on the earth, and particularly in the poorer desert regions of the earth and we do nothing with it is just absurd. And of course we will. And of course we are doing. And the economic equations are changing all the time. And people used to say, oh yes, well, we can get fresh water from sea water, but of course it's fast and expensive. It isn't so if you can actually get enough solar power to deal with it. And if you get enough water in parts of the world, from now desert and start watering the desert and making the desert bloom, you can change lots of things. At what stage does human beings begin to understand about the problems of dense populations? That's a job for sociologists and other people who study these things to convince politicians of what we're doing. But convincing politicians is not enough. You have to convince electorates. And there has been, I think, I mean, a lot of people are very pessimistic and doom laden and so on. And so the green movement has got anywhere. The green movement has made huge strides. It is astounding the effects of the green movement. The fact that governments are prepared to make sacrifices to put in place a policy, the benefits of which will not be apparent long after their electoral period. That is a huge advance. And fair play to the electorate. It is the electorate that has demanded that they do that. The green party has demanded that they do that. And the green party has remarkable support. But even more important, perhaps, is the fact that there are green wings, as you might say, to every political party. No party now can get into power unless they could say something about what it was going to do with the environment. Well, that is a huge plus for those who are concerned with educating the British electorate on environmental issues. The Welcome Trust is such a unique organisation, I mean, with the sort of income that it has and the sort of funds that it has. And thank God it has administrators who are wise and who are scientists, which is a crucial thing, and not politicians. And there aren't lots of organised, many organisations in the world that I can think of like that. So, if it's not unique, it's very nearly unique. And to have great economic power and scientific insight is a very powerful pairing that can be, could be, and is very effective. We know it. I mean, it doesn't beat the drum about what it does, but actually the number of places where the welcome name is there unobtrusively at the bottom, whether it's dealing with cancer or whether it's dealing with educational problems and so on, is huge. And I don't know whether Sir Henry had any idea of what he was going to do or how wealthy his foundation was going to become. But he certainly left a great boon into the world.