I definitely agree that Andalites probably live longer than humans. Like others have said, Alloran was a full-grown Andalite in HBC, yet he sure didn't seem to be in his 70s or 80s by the end of the series.
I don't think we can trust book #8 for an exact statistic, though. After all, wasn't that also the book where Ax said that the Hork-Bajir have a biological clock that set them warring every however many years? And yet, in HBC, Dak has no idea that he can use his blades to hurt people.
Actually I got to thinking about this at work (don't ask why, it just popped in there) and I realized the Andalites live for a very long time but reach maturity very quickly. If an Andalite year is like 6 earth years and Ax expects to live 200 andalite yers (when he says that he could live to be 200 years old he doesnt say "earth years" so I figure he means Andalite years) simple math says that's about 1200 years. Now given that Ax is born not so long before Tobias, who was 13 at the start of the series Ax would be about 2 or 3 Andalite years old, yet is already an adolescent.
If Andalites reached sexual maturity at, heck lets say 5 years the've got 195 more years to keep on reproducing and reproducing, their birthrate might be slow and their term long but didn't the Ellimist have 3 surviving Andalite children, and others who didn't? That was the prehistoric andalites, they would have technology by now that would better keep most infants from dying at birth or later from illnesses, and while this might explain why present-day Andalites had restrictions on how many children were allowed to be born outside of war (As stated in the Andalite chronicles) in the thousands of years before they reached that point in time with their natural predators wiped out they'd overrun their grazing areas and have to live in the harsher areas or die of stavation.
So in short, Andalites might have a small controlled population now, but you'd think at some point sheer numbers would have forced their ancestors to explore more of their world . . . then again, maybe they fought a lot of wars, they have a proud warrior tradition after all. Even so I think they'd have to have migrated to various parts of their planet early on, so they should have evolved at least some differences . . .
So yeah, this is what came to me at work . . . you can tell how much I love my job when I start considering the lifespans and evolution of alien species -_-
First off, it was pointed out earlier that slow maturation would also slow down evolution. Maybe they couldn't cope with the new environments quickly enough to make the switch. Also, what you said about their technology (and the absence of predators) enabling them to spread to all corners of the world has a flaw . . . Because you know what else slows down, and maybe even stops, evolution? Civilization. In a world where it's no longer survival of the fittest, and just survival of everybody, how can you have evolution? Sure, the outright
vecols are eliminated from the gene pool, but everyone else lives happily ever after. No, I'm talking about evolution that happened in prehistoric times, before civilization happened.
Anyway, next point. We've said that slow-aging could slow down evolution, as would be the case with Andalites and Yeerks. What about the Hork-Bajir, though? They must age insanely quick, because Toby, who was born sometime after book 13, was just about grown up by the end of the series. By the same logic that we're using for the Andalites that they
shouldn't evolve as fast, the other side of the coin is that the Hork-Bajir should evolve at absolutely ludicrous speeds.