Why aren't we hip-deep in Martians?

The Universe is amazingly hospitable to life.  That may seem an odd statement at first, considering as most of it is made up of hard vacuum.  However, consider that the laws of physics are such that planets with atmosphere can form at all (what if gravity didn't exist?), or taking it even further back, that matter can form at all, and that the amount of matter and antimatter after the Big Bang wasn't precisely balanced so that a decent amount of matter was left.

Some would say that this is evidence of a divine creator, or at least suspicious -- how did we end up with a Universe so hospitable to us?  But this is circular -- what other kind of Universe could there be?  If the Universe were not well-suited for evolving us, we wouldn't be here to complain about it -- instead there would either be no life at all, or perhaps more likely, a completely different form of life that would itself be wondering how it ended up with a Universe so perfectly suited to it.  And it's kind of an odd thing to ponder, the probability of the Universe being any certain way, as we don't have any other universes to compare it to.  Without a baseline, how do we know if our particular set of cosmological constants and matter/energy balances is peculiar?  Maybe all universes are like that.

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