This doesn't imply there is one beginning, I think (with no attempt at proof) it's possible there were multiple, but it's pretty easy for things to get wiped ou

This doesn't imply there is one beginning, I think (with no attempt at proof) it's possible there were multiple, but it's pretty easy for things to get wiped out and to lose part of the chain. The last universal ancestor is just the one that you can get to by not breaking the chain. As to your questions, they have vexed scientists and philosophers for ages, so there're no easy answers, but I am assuming you didn't expect one! The conditions for life as we know it are bounded, so that reduces the surface area of possible places life could exist. Add to that, the requirement that the bounds not change dramatically for long periods of time, and they reduce further. The universe is pretty huge, though, so there's a lot of opportunity for life out there, but because it's so huge, and because life is so fleeting, there's a lot less opportunity for two unique forms of life from different planets, solar systems, or galaxies to actually cross paths at the same time, or even to do so before one dies off. For further reading, check out the Drake Equation [1] and Fermi's Paradox [2]. [1] http://en.wikipedia.org/wiki/Drake_equation http://en.wikipedia.org/wiki/Drake_equation [2] http://en.wikipedia.org/wiki/Fermi_paradox http://en.wikipedia.org/wiki/Fermi_paradox