Humans, the latest novel from prolific science fiction writer Robert J. Sawyer, is the second book in his Neanderthal Parallax trilogy. The novel begins with Neanderthal scientist Ponder Boddit deliberately reopening the quantum rift that creates a pathway between his world, where Neanderthals developed into the dominant species, and our own. Boddit, accidentally trapped in our world in Hominids, returns as a special envoy, leading a delegation of Neanderthal scientists and artists to create a cultural exchange between the two worlds. Boddit also returns to his fledgeling relationship with human geneticist Mary Vaughan, now working for an American government think tank.

The Neanderthal Parallax is tremendous storytelling, with a convincing (if not always firm) scientific basis, but at its core, it is science fiction as social commentary. Unfortunately, Sawyer’s exploration of the human world is heavy-handed when compared with his depiction of the mores of the Neanderthal culture in Hominids. Where Hominids succeeded brilliantly with a canny, sidelong critique of contemporary human culture through an implicit comparison with Neanderthal culture, Humans is freighted with simplistic, pedantic, and repetitive social commentary that frequently stops the narrative in its tracks.

Sawyer is more successful when he allows emotional relationships to create a more genuine sense of cross-cultural insight. The passage in which Vaughan witnesses a Neanderthal bonding ceremony says more about comparable social fabrics and beliefs than does the far-too-preachy visit to the Vietnam war memorial in Washington. Too often the prose in Humans is gimmicky and rushed, especially when compared to the preceding volume. The concluding events also seem forced and may foreshadow an easy moralizing conclusion that one hopes Sawyer will avoid in the third novel.

Like most of Sawyer’s writing, Humans is worth reading for the things it does right: the quality of Sawyer’s vision and insight, the near-possibility of his scientific departures, and the depth, if not always the execution, of his social criticism.