(Brief notice from unhappy robot: I'm left-handed and my left hand is currently in battle with a wrist splint. Typing blog entries is, for the moment, not high on the list of great things to do. I'll post more frequently when it doesn't make me grimace.)
I... yeah, I bought this an embarrassingly long time ago, together with its sequel, and, you know, didn't read it before now. That's just how stuff turns out. Stupid stuff, because The lives of Tao is so much fun. (My first association would be Flex, which I read recently - the pace and tone is something in that direction, though the genre is very much science fiction, and also it is awesome. )
You have no idea, or likely interest, in how much I think about different alien invasion and first contact scenarios. (My cohabitant knows, though. He has a special face for every time I start a sentence with "Heyy, you know what kind of alien would be cool?" Admittedly, you could replace 'alien' in that sentence with 'plague' or 'dinosaur' and it'd still be quite true to life.) Um. I mention this because I've really, really wanted exactly this story to fall into my hands. I've actually said the words "I need more books about aliens guiding human evolution, right? Like, they've been here all along just waiting for us to become useful, and..."
That's The lives of Tao. Tao is an alien lifeform who cannot live in Earth atmosphere without taking a host and thus exist as a symbiont. (This is smoothed over and doesn't go into rock hard science detail, which, honestly, is fine. It's alien.) Once he inhabits a human, Tao can speak in-brain to that person. He's been around for a few geological eras, so he has a lot of stories to tell and stuff to teach, though, unfortunately, a lot of it has to be about combat skills, because Tao is fighting a war with an opposing faction of his own species.
Roen Tan, the accidental host, does not share Tao's clear goals. He couldn't even get himself out of a job he hated, on his own. Or lose the pizza-every-day belly. Becoming invaded by Tao changes this, which is good - but he is now recruited to be a part of the war, which doesn't appeal to Roen at all.
This book was awesome, and I'm going to read the rest of the trilogy ASAP. Highly recommended as a cool parasitic/symbiotic alien thriller full of warmth and laugh and, uh, a bit of Genghis Khan. If you don't like this book, I'm guessing it's because you're even more vehemently bored by gunfight thriller waffle than I am, which is quite a feat, actually.