So, how did this idea of ancient Boskops make it into a book by two neuroscientists in 2008?

If not through science, then possibly from science fiction. The "Boskop race" was immortalized in popular writing by Loren Eiseley, who included an essay on Boskop Man in his collection, The Immense Journey, first published in 1958. As you can see, by this time the entire concept of a "Boskop race" had fallen into scientific disrepute. But Eiseley was undeterred: he conjured the idea that the Boskopoids were advanced in their large brains and small faces -- the apex of a trend toward paedomorphism, the retention of juvenile characteristics. In this state, they resembled what Eiseley suggested would be the "Future Man": We can, of course, repeat the final, unanswerable question: What did this tremendous brain mean to the Boskop people? We can marvel over their curious and exotic anatomy. We can wonder at the mysterious powers hidden in the human body, so potent that once unleashed they brought this more than modern being into existence on the very threshold of the Ice Age. We can ...  more