Hallucinogens and evolution

From an interview with Graham Hancock
in The Daily Grail's online mag, Sub Rosa:

"It's just amazing the way the archaeological record 'lights up' after 40,000 years ago with incredible symbolism, the appearance of the first art, evidence across a whole spectrum of activities of exactly what we would recognise as completely modern human behaviour, and it seems to switch on very suddenly. I realised that this is where the mystery lies, this is the mystery that I want to explore. Whatever it was, this process that made us human, right there at the very beginning was art, and incredible symbolism...the art of the painted caves of Europe for example, going back 35,000 years.

"When I started to look around in this field, I found that cave art specialists had been squabbling for the best part of a century, but since the 1980s one very powerful and increasingly well accepted theory has been put forward, which suggests that this amazing adventure of art and religion at the beginning of modern behaviour was inspired by taking plant hallucinogens, by inducing altered states of consciousness, and painting the visions that our ancestors saw in those states. Once I realised that was a real possibility, then it opened the door to all the other areas of inquiry in Supernatural: Meeting with the Ancient Teachers of Mankind [Hancock's latest book, which is available now in the UK; US release in 2006]."