And that sample of one actually shows that intelligent life can exist for evolutionarily long periods without advancing much technologically. We spent over 3.3 million years using stone tools. The Neolithic only ended about 6.5 thousand years ago. The period we spent slowly refining stone tools was over 500 times as long as the entire period from discovering how to use copper to landing on the moon. Whole new species of humanity evolved and died out in that timeframe.

And animal life had been around for about 500-600 million years before the first humans popped up. It took until a couple hundred million years ago for the first mammal-like species to show up. And there's evidence that single-celled life first showed up about 3 billion years before the first animals, about as soon as Earth could support it.

From that single example, it looks like a planet could potentially spend a very long time without animal life, with only non-tool-using animal life, or with intelligent life but very primitive technology, and that none of these steps are particularly inevitable. Or it could have gone much faster than it did here. Other examples, if we ever find them, are likely to have quite different histories.