> Hence either foreign life form X were far more likely to develop and we would see it all over the place (actually, maybe not), or it were far less likely and

> Hence either foreign life form X were far more likely to develop and we would see it all over the place (actually, maybe not), or it were far less likely and hence we'd rather find one similar to ours. Yea. The argument is actually independent of whether the probability of abiogenesis is large enough for life to independently arise multiple times in the solar system or (conversely) small enough that it's very unlikely for it to exist elsewhere in the observable universe. I think all it requires is that abiogenesis is a combination of several small probabilities distributed over several orders of magnitude. (If the probability is large enough that multiple forms routinely develop on the same planet, then we probably also have to assume something about, say, the first-mover dominating.) > But how does one estimate probabilities of abiogenesis, or their relative magnitudes? It's really hard. > Are there e.g. scientific papers published on this subject? Yes, but I don't know them off the top of my head, or whether any are any good.