I like this idea. I’ve thought of a similar idea at the other end of the limit. How much less intelligent could a species be and evolve to where we’re at? I don’t think much.

Once you reach a point where cultural inheritance is possible, things pop off at a scale much faster than evolution. Still, it’s interesting to think about a species where the time between agriculture and space flight is more like 100k or 1mm years than 10k. Similarly, a species with less natural intelligence than us but is more advanced because they got a 10mm year head start. Or, a species with more natural intelligence than us but is behind.

Your analogy makes me think of boiling water. There’s a phase shift where the environment changes suddenly (but not everywhere all at once). Water boils at 100C at sea level pressure. Our intelligence is the minimum for a global spanning civilization on our planet. What about an environment with different pressures?

It seems like an “easier” planet would require less intelligence and a “harder” planet would require more. This could be things like gravity, temperature, atmosphere, water versus land, and so on.