How did intelligent life evolve?

It's an interesting question that I had while reading the book too, especially given how short even the "stable" eras were depicted as being. One possible answer is that the repeated extinctions selected for organisms that could retain memories and skills during dehydration and basically pickup where they left off. I settled on thinking of the San Ti as highly evolved tardigrades which, on Earth, can go dormant and survive any number of insanely harsh environments. Now... that said, we don't see any highly evolved tardigrades running around on Earth. Basically down to suspension of disbelief I guess. Honestly I think the author just felt that the three body problem (the astrophysical one) was just really cool and so just used it as a plot device in the book as a way to highly motivate the San Ti to find another planet vs. just making them aggressive/hostile for no explained reason.

I'm going thru reviews of the book and trying to understand what people like in it, because to me the book looks pretty stupid. People point out to few cool ideas, although some of them are pure fantasy obfuscated in scientific terms to make it look plausible ("Oh, my reader, you are too dumb to understand my super smart book, so you better like it to look like a smart chap"). For me cool ideas don't count if the book taken as a whole is lame, but at the same time trying hard to be grand.

Civ emerging in extreme conditions is one of those interesting ideas. My understanding is that sometimes stable eras lasted long enough, or the bad eras were not catastrophically bad, and that allowed the aliens to understand their predicament and try to solve it. We don't really know how much time is needed for a scientific civilization to emerge from primordial soup, because we have only one example. Till 65 millions years ago things were at a dead end, but then things rapidly (in cosmic scale) changed.

As it is situated in the book, the stasis of which this creatures are capable won't help in the most extreme conditions. Actually the planet will be either destroyed in short order or beaten up so badly that even a slug won't evolve. In reality, such planet, if survives, it would lose its water and atmosphere and its surface will be defaced by the volcanic activity caused by the ever changing pull and twist of the three suns. And if I want to be nitpicky, Alpha Centauri is nothing like that and till now there are no triple body problem stars found - either they star formation process leads to stable orbits or one of the stars gets quickly destroyed. It is worse, because if aliens were in Alpha, the would know about us and no need to send signals. Even with our current tech we are aware of planets in Alpha, some potentially habitable. Of course, the author put the aliens there so that the characters can communicate with them. It is this much contrived and I hate it.