Dear Mr Porritt, I heard you on the BBC the other day, and you had some interesting things to say about population control. I understand that you are the chair of the UK government’s Sustainable Development Commission and so your ideas are not without consequence. Your argument was thus: people use the earth’s resources, and those resources are finite. If we increase the number of people, resources will decrease faster. If resources are finite and numbers of people increase, then at some point in time we will be in danger of running out of resources. Therefore, you conclude, we should limit the growth in numbers of people. In essence you…