First, I want to fully admit I didn’t watch the video. Apologies ahead of time if that causes me to be redundant or reductive.

Second, I’m also a biologist, although a molecular one.

Third, I agree with almost all of your premise and train of thought. We’re certainly more likely to get the likes of “bacterial mats” than intelligent life anywhere, and especially within a distance that we will ever realistically encounter.

I do wonder, though, how you (or maybe the video guy, but obviously not enough to watch the source material before making an ass of myself…) conceptually reconcile the small sample number of known planets with life (n=1) with the mindblowingly impossible number of worlds.

You say that intelligent life involving only once indicates that it is difficult for evolution to “discover”, which is surely possible to be true. But given that we haven’t seen the evolutionary conditions on other hypothetical worlds, from what we know, the evolution of intelligent life has a perfect 100% success rate of occurring on planets with life.

In fact, you mention the independent convergent evolution of eyes as an indication that eyes are a “good idea”, and that they must be relatively easy for evolution to discover if they evolve independently, repeatedly. But evolution is subject to the whims of selective forces, so a different world would surely select for different traits. Eyes (or other extremely common evolutionary pathways… looking at you, crab body) might be less frequently selected for or be entirely useless, but intellegent decision making and tool use might evolve in ways we can’t even conceptualize in our context.

This also extends to the claim of how our world is evolutionarily dynamic (which you point out is hard to quantify in context). We don’t know the dynamics of evolution on other worlds, if it happens at all. Recombination could be a unique characteristic of DNA-based life on Earth or it could be extremely common. Other worlds might have longer or shorter evolutionary time lines, also, since our sun’s “working life” is shorter than average due to its size and density. Without another example for reference, we don’t know whether we’re evolving quickly and with diversity or slowly and conservatively.

I guess, I don’t think you are wrong, exactly. I just think you are necessarily making assumptions based on how things work here in order to extrapolate how things might work there– one has to! But the whole discussion (which continues, like this, to this day) revolves around just too many unknowns. We just don’t know, and can’t know.

Climbing down from my high-horse, though, I have to admit I’m biased, since I have a pet-belief that life is basically guaranteed to exist elsewhere (how freakish would it be for it to only happen once out of so, so many chances?). I honestly feel like there’s a good shot that it’s incredibly common, at least in a basic form. In essence, I suspect that if we find bacterial mats (or soup) on Enceladus or Europa then it’s basically certain that life is everywhere. But we won’t even likely know that in my lifetime, so…