Re: Leslie's "The End of the World"

Nick Bostrom (
Sat, 15 Aug 1998 01:52:36 +0000

Robin Hanson wrote:

> >If postbio and bio intelligences all belong to the same reference
> >class (just as tall people and short people, black and white etc.)
> >then the fact that you find yourself being a bio intel. would
> >indicate that the postbios don't vastly outnumber the bios.
> >
> >Whether postbios and bios should be in the same reference class is
> >not clear. That's a deep problem, and I suspect but am not yet
> >certain that there might be some kind of loophole for the
> >transhumanist here, if the postbios are fundamentally different from
> >bios.
> I reread Leslies book on this issue last night, and object to
> putting bios and postbios into the same ref class in exactly the way
> that Leslie envisions one might object:
> It might perhaps be complained that making the reference class into
> humans-after-splitting-away-from-Neanderthals would be coming too
> near to imitating the man who makes his reference class into
> people-born-as-late-as-himself-or-later [p. 261, The End of the World]

The complaint that Leslie is refering to is that the reference class should not be unduely *narrowed*, that it would be wrong to leave out the pre-Neanderthal people. What you are saying is that the reference class should not be *widened* to include postbios. So why do you say that you object in exactly the same way as Leslie envisions? As far as I know, Leslie has never considered ruling out postbios from the reference class on the ground that they would be too different.

> If you do a Bayesian analysis of all your information carefully, the DA
> effect will be embodied in your analysis, and should not need to be added
> in seperately.

True. The reason why we might want to add it in separately is to more clearly see what effect it should have on our belief system.

> I'm now reading your paper on the DA, and hope to write a summary
> of my opinions on DA soon.

I look forward to that.

[I should say that the formulae in my "Investigations"-paper apparently don't display properly. But it is possible to download the document as a Microsoft Word file from I also have two shorter papers there.]

Nick Bostrom
Department of Philosophy, Logic and Scientific Method London School of Economics