@Setanta,
Setanta wrote:
As for the rest of Mr. Cox's thesis, i agree that complex life forms are far less probable than has commonly been thought, but i don't see any reason to assume that the odds against it are almost insurmountable. Complex life forms may be extremely rare, but i see no reason to assume that they're nearly impossible.
If I understand correctly, I think his claim is based on his understanding about the probability of single cellular organisms evolving into multi-cellular organisms. But I don't have access to the data he may have used to calculate that.
However, that particular evolutionary step would seem to be critical in the evolution of technological intelligence (at least if we keep our view of "life" to the narrow band of water based organics which we are familiar with), so if for some reason the probabilities of that happening are small enough, then the stability period for planets or moons may be too short to allow for it in a single Galaxy.