That's ignoring an anthrophenic argument and the finiteness of the observable universe. The probability for life to evolve on any given planet may be 10^-100. B

That's ignoring an anthrophenic argument and the finiteness of the observable universe. The probability for life to evolve on any given planet may be 10^-100. But because we obviously observe the planet where life happened to evolve, we cannot tell whether the probability is 10^-100 or 1/10. That would mean that it would most likely only happen once in the observable universe, and the next instance may be many universe distances away. That would make us alone, even if we assume that the universe is infinite.