The Doors of Eden by Adrian Tchaikovsky, 627 pages
Four years ago, Mal disappeared while monster-hunting on a moor with her girlfriend, Lee. Lee assumed that Mal was dead, but as it turns out, she was simply trapped on an alternate Earth, living with the dinosaurs there. It turns out that there are several Earths, each with a different evolutionary path that branches off at different catastrophic points in time. Oh, and the walls between them are slowly becoming more and more porous, leading to what may be the final, all-Earths catastrophe.
Massive in scope and insanely creative, this book brings together the smartest (or at least most dogged) beings from several Earths, fending off their own prejudices (and evil opportunists) to try to solve the problems of the multiverse. I particularly liked what Tchaikovsky had to say about human intelligence, as well as our consideration of "the other." The interstitial chapters from an academic book about the multiverse are sometimes a bit plodding, but they're much shorter than the action-filled chapters and they do have a point, so it's better to read them as you go. It's a big book, but for someone looking for a new take on evolution and the idea of parallel universes, it's definitely worth the time.