It's fascinating to me that the complexity of life always goes up. Outside extinction events, complex life generally seems to become more favourable over time. It's interesting that (to my knowledge) we don't see an ecosystem lose complexity in its entirety unless it's dying. Simple organisms make a bedrock for complex organisms, and while the complex organisms have more specific needs, they are better at exploring,…
I would say we have a complex organism bias though, really the most successful life is simple, more than 90% of earth's biomass is plants, ants, fungi, bacteria (obviously some of those are more complex than others, but none of them are posting on HN quite).
Sounds like the complexity of life follows a power law distribution, where most of it is simple to moderately complex, but a few species are orders of magnitude more complex than the vast majority. Eg, the vast majority of complexity among living organisms derives from just a few species.