The world’s footprint measure seems better. But what exactly counts as environmental virtue? In which important ways will the environment degrade if the total human footprint exceeds the available area? Put another way, should we be making the environment better for humans to live in, or for animals and plants to live in?

Or do we try to minimise our impact and leave the other species to their fates? This amounts to partitioning the earth into two environments and reducing the net flux between them. Domed cities and space bubbles might be cool. But assuming animals aren’t worthless, who manages the natural environment then? Does nature really know best, given that it has destroyed more than 99% of all historical species?

If we refuse to allow existing species to continue to die out, should we preserve them by gardening the earth and, as a side effect, allowing their fitness to deteriorate? Or should we merely collect their DNA, and the DNA of as many extinct species as we can find?