This Summer I plan on reading:
The Neanderthal Parallax  - A trilogy of novels by Robert J. Sawyer . It depicts the effects of the opening of a connection between two alternate Earths: the world familiar to the reader, and another where Neanderthals became the dominant, sentient hominid. The societal, spiritual and technological differences between the two worlds form the focus of the story.
The trilogy's volumes are titled Hominids, Humans and Hybrids.