This is the second installment in Robert J. Sawyer's Neanderthal Parallax trilogy. In it, Ponter Boddit, the Neanderthal Physicist, returns to our universe and pursues his relationship with geneticist Mary Vaughan. The story is predictable, as is the inevitable climatic scene, and it left me feeling unsatisfied. On the other hand, Sawyer has introduced a new element in this story that's likely to cause a more intense conflict in the 3rd book.
Over all, I enjoyed this novel, but not as much as I enjoyed the first book (Hominids.) As I said earlier, the conclusion was inevitable, and Mary's reactions were too clinical and dispassionate to really engage my interest. The quantum mechanics tie-in is too dubious for me to accept, and I think, if I see where this series is going, it will leave me feeling dissatisfied. On the other hand, speculative fiction writers who struggle to make the science worthy of the story are more engaging than those who struggle to make the story worthy of the science.
Recommendation: Borrow it.
Humans (Neanderthal Parallax) by Robert J. Sawyer