Indeed, I infact think that the 4th is certainly true to some degree, the majority of the time when people discuss this they don't even consider things such as silicon based lifeforms, and yeah, I think I wrote the description bad (I'm a physicist, not a biologist :P). However, I don't think that 4 alone completely answers the question. The majority of the physical constants would, if changed give life to different forms of life. I doubt carbon, water, air that we would refer to as breathable, or even an amount of sunlight such as we would consider essential is actually required for life.
But the gravity example, I honestly cant stretch my imagination far enough to allow for intelligent life to evolve in an incredibly short, hot and fiery universe that would exist if gravity was much stronger.
