The following is obviously true:
- Any world that contains an exact duplicate of the solar system, over all its past, is a world that contains human-type mental states.
But now we see that Humeanism about laws plus naturalism about mind requires us to deny (1). For we could imagine a world with an exact duplicate of the solar system but where the behavior of stuff outside the solar system is so very different from how it is in our world, that the familiar sorts of laws that are crucial to our mental functioning being as it is do not hold, say, the Pauli exclusion principle is false, though by chance the local behavior in the solar system is as if those laws held, so in our solar system, fermions don't share a state. But without such laws we don't have the kinds of functional interconnections that are involved in human-type mental states.
I suppose the Humean might just deny (1). But now we can make it more ridiculous. On Humean views, what laws there are depends on the future course of the universe. Imagine that we have a universe which is just like ours up to tomorrow, but with an infinite future a day later, where everything goes topsy-turvy. None of the regularities that held up to tomorrow are global regularities, and a fortiori none of them are laws. Therefore, in that world, too, there haven't been any human-type mental states. And that's really absurd. For it means that whether there have been human-type mental states depends on how things will be from the day after tomorrow.