Excerpts from Robert Nozick's "Invariances" Necessary truths are invariant across all possible worlds, contingent ones across only some. No wonder necessity lures philosophers. It is the flame, the philosopher the moth. Our intuitions that certain statements are necessary do not powerfully support this claim when natural selection would produce strong intuitions of their self-evidence, even were these statements (only) contingently true. Contemporary philosophers who give great weight to intuitions need to offer some account of why such intuitions are reliable and are to be trusted. Of course, if the purpose of such philosophy is merely to codify and systematize the intuitions that (for whatever reason) are held, then a philosophy built upon intuitions will need no further basis. And it will have no further validity. You might think that an insight into metaphysical impossibility could save the physicists much useless work by thereby excluding something as physically possible. Things seem to have worked in the opposite direction, though. Driven by a need to explain strange data, physicists formulate theories that countenance what previously was held to be metaphysically impossible. . . The physical tail wags the metaphysical dog. Why is there an objective world? Within evolutionary cosmology scientific laws might be viewed as the heritable structure of a universe, akin to what in biology would be an organism's genetic endowment. . . Suppose that the reproductive process of a universe produces transformed offspring universes that differ from their parent. The greater the transformations that a law is invariant under, and the wider their number, the greater is that law's heritability. The vast majority of the universes that exist through the processes of evolutionary cosmology, therefore, will exhibit laws that are invariant under a wide range of significant transformations. Such invariance, we have seen, is exactly what constitutes objectiveness. Evolutionary cosmology gives us objective worlds.