Cool, I like these sorts of discussions.

It is certainly relevant to think about whether intrinsic worth does guide our ethics, and looking at my last posting I have noticed an apparent inconsistency in extrapolating from the worth an animals life has to him/her to intrinsic worth. But the point I was trying to make is that we use the same extrapolation in our (often unstated) assumptions that human life somehow has intrinsic worth.

In other words we use the maxim "do unto others as you would have them do unto you", and apply it to other humans. But this maxim could equally be applied to any sentient being with an interest in staying alive, experiencing pleasure and avoiding pain. So if we are basing morality on the "golden rule" we are assuming intrinsic worth.

I teach environmental science and one of the debates I use is whether nature and ecosystems have intrinsic worth or are just instrumentally valuable to humans and other animals. Trees and ecosystems cannot feel pain, or pleasure (or so most would believe), so the "golden rule" argument would not apply to them. But most people intuitively believe that it would be morally wrong for the last sentient being on earth to cut down the last Kauri tree. Environmentalists therefore also seem to base decisions on intrinsic value. And in fact the intrinsic value of biodiversity is part of the government's biodiversity strategy.

Phil