I strongly agree with you about human hubris. I think it's very unlikely we're the smartest living things in the universe. Also, we're not as different from other living things on Earth as some of us have supposed. Hubris can lead to think our intelligence makes us invulnerable, which we're certainly not... Though right now I think we have much more to fear from harmful side effects of our own technologies, especially climate change, than from alien invaders. Regarding Darwin, I'd agree that he didn't know everything. Does any scientist know everything? I haven't read the Tangled Tree, but I understand it is largely about the work of Carl Woese, another important scientist who certainly contributed to our understanding of micro-organisms and early evolution. Regarding the start of life, it's been one of the great unanswered questions. Darwin said very little about it. Do you know of the recent work by Bruce Damer and David Deamer on the land hot springs hypothesis? It looks very promising.