Chemistry’s the limiting factor for most of it. You’ll need a lot of energy for complex life. The list of things that can naturally provide enough without havi

Chemistry’s the limiting factor for most of it. You’ll need a lot of energy for complex life. The list of things that can naturally provide enough without having extremely-hostile side effects is pretty much limited to stars, and then only if you get really lucky in a whole bunch of ways. Then you need to turn that into chemical energy to actually do anything with it. That’s gonna turn useful chemicals from the environment into waste you can no longer use. If you’re lucky the waste is chemically useful, and if something can evolve to use it, maybe it can turn it back into what you need (happened with oxygen). If the waste isn’t useful, you better hope your planet’s recycling it somehow. Ideally with some kind system that adjusts with a feedback-loop so it doesn’t limit your growth too much. Our one example sure looks extremely fragile, in that if you mess with any of several things a little bit, you might still get life, but it’ll cyclically wipe itself out, or never be able to harvest enough energy to support complex life, or any number of other problems that end in not seeing intelligence arise.