Approaching Charlotte Square from George Street, I spot Ian Rankin. Standing across from me on the traffic island, waiting for the lights to change, talking nicely to a couple of starstruck American tourists in pink jumpers. Then a bus passes between us, and he vanishes.

Inside, a toddler solemnly wades in a mud puddle at the edge of the grass. Everyone is sneezing in the press pod; the perfect order of the novelty igloo has been mildly disrupted by a growing stack of newspapers and a discarded wine glass.

In the Peppers Theatre, Andrew Parker is presenting his book The Genesis Enigma, a peculiar investigation into the possible coexistence of the Darwinian theory of evolution, and the Biblical creation narrative. There are a few similar events at this years book festival, on the 200^th anniversary of Darwin's birth and the 150^th anniversary of the publication of Origin of the Species.

Thankfully, for those of us who aren't sciency, Parker explains his book in pretty simple terms. The project sprung from his earlier book on evolution The Blink of an Eye, which resulted in a pelting of letters from US evangelists who claimed that Parker was actually describing the book of Genesis. Initially dismissing all this, Parker then happened upon an Oxford discussion group set up to find intellectual merit in creationism.

Erm, yes...Parker makes it clear that he doesn't agree with creationism, but presents the idea that the first book of Genesis has glaring stylistic differences from the rest of the Bible, lending interest to the reasons for pasting it right at the front of the book.

Another curiosity is the similarity, if we look at the Genesis story metaphorically, of the stages of creation with the stages of evolution. First there was sky, then there was water, then life. Parker points out that the style of storytelling when the Bible was compiled tended to be metaphorical. He also goes into some detail about the Cambrian Explosion, and Darwin's difficulty with the sudden appearance of fossils.

The casual Ian Rankin spotting echoes a conversation I had last night with my flatmate, an Edinburgh native, who recalls the days when the Book Festival was just a murmur in the larger racket of the Fringe. We both observed, though, that even with the advent of celebrity novelists, Scottish culture doesn't really allow for fawning. I can't quite imagine Liz Lochhead striding along Sauchiehall St with a couple of man-mountain bodyguards.