[cgriswald]

The main problem we have in the search for extraterrestrial life is that we really do not know much about life. We know a reasonable amount about Earth life, but that's about it. I have read only portions of Rare Earth for my research and plan to return to read it through. But some of the arguments made seemed to rest on a lot of supposition. I'm not convinced they're wrong exactly.

I think there may be many "Great Filters" to explain the Fermi paradox, and the rise of metazoans may be one of those filters. But I'm not necessarily convinced that complex life requires, for instance, a large moon to stablize the tilt of the planet. Evolution seems a little more robust to me.

I do not know if they mention this in the book or not, but I am afraid that the transition to land may be infrequent (many worlds may not even have land above sea level). Even if dolphins or whales were as intelligent as people want to believe, they are unlikely to ever develop space travel or even radio communication.

I'm equally on the fence about the mediocrity principle. Maybe complex life takes a long, long time and Earth somehow got lucky. We are already freaks because we orbit a G-type star. Most stars are M-type (red dwarfs). They are very long lived and have plenty of time for life to form and evolve on planets around them. Put another way, maybe somehow we are just "first".