Thank you.
This is an excellent question and one that I grapple with in many ways, often in the media, but also just with myself. Why do we care about biological diversity?
One of the answers to that question, of course, was touched on extremely ably by Professor Chan: that species do things that matter and that sometimes they do things that matter to us in ways that we fail to measure in economic terms. This is really important, this notion of externalities: that we derive economic benefits from species in a diffuse manner, but that we don't measure those economic benefits all too often. The consequence is that when we inadvertently drive a species extinct without being aware of what we're doing, the cost of that is zero because it's not something that we measure the impact of. That's something that I think we need to be very careful about. There are better ways to do this.
Another element of this, from my point of view, is that if we reduce everything to the question of whether species X, Y, or Z has sufficient economic value in any given instance to prevent development or to alter the way development is conducted, then in many instances—and I suspect even in most instances—what's going to happen is that the decision will be that in the exact location where development is proposed, the specific economic return of biodiversity in that place is relatively small. We can make that decision a million times, and the consequence is that we find ourselves in the midst of a global extinction crisis that we haven't seen in 65 million years. That is literally true.
I have to say that this is a concerning question, but the thing I would say in conclusion—I know that I have to wrap up—is that it's not really about the money. It's about what kind of world we want to live in, and that's a decision that we take away from our children by continuously conceding that in any given instance we are always going to side with a short-term economic perspective.