The book's title refers to the 1856 discovery of a clearly very old skull cap in Germany's Neander Valley. The possessor had a brain as large as a modern human, but a heavy low braincase with a prominent brow ridge. Scientists tried hard to explain away the inconvenient possibility that this was not actually our direct relative. One extreme interpretation suggested that the preserved leg bones were curved by both rickets, and by a life on horseback. The pain of the unfortunate individual's affliction had caused him to chronically furrow his brow in agony, leading to the excessive development of bone above the eye sockets.
The subsequent history of human evolutionary studies is full of similarly fanciful interpretations. With tact and humor, Tattersall concludes that we are not the perfected products of natural processes, but instead the result of substantial doses of random happenstance.