We need to learn how to capture and kill wild fish humanely - or, if that is not possible, to find less cruel and more sustainable alternatives to eating them.

Take for example providing a guide dog for a blind person. That's a good thing to do, right? All right. It is a good thing to do. But you have to think what else you could do with the resources. It costs about $40,000 to train a guide dog and train the recipient so that the guide dog can be an effective help to a blind person. It costs somewhere between 20 and $50 to cure a blind person in a developing country if they have trachoma. So you do the sums, and you could provide one guide dog for one blind American or you could cure between 400 and 2,000 people of blindness.

Somebody who eats twice as much factory-farmed products as he or she needs to is clearly doing twice as much damage to the planet. From a utilitarian point of view, that's twice as bad.

My work is based on the assumption that clarity and consistency in our moral thinking is likely, in the long run, to lead us to hold better views on ethical issues.

Well the real concept of basic needs if you cut it right down are simply the physical needs that are unavoidable for all of us. So to have enough calories to keep our bodies going. Have shelter from extreme elements. To have water that is safe to drink, So I think that's the core of it.

If you're buying animal products and can go to the farm and actually see how the animals are looked after, yes, that's an important point. That's definitely the best way of assuring yourself that the animals are being well treated.

There has been opposition to experimenting on animals for a long time. This opposition has made little headway because experimenters, backed by commercial firms that profit by supplying laboratory animals and equipment, have been able to convince legislators and the public that opposition comes from uninformed fanatics who consider the interests of animals more important than the interests of human beings.