The actual paper behind this talk is here: http://www.sciencemag.org/cgi/content/full/316/5827/998?ijkey=9S1Vi6nUWCqY.&keytype=ref&siteid=sci http://www.science

The actual paper behind this talk is here: http://www.sciencemag.org/cgi/content/full/316/5827/998?ijkey=9S1Vi6nUWCqY.&keytype=ref&siteid=sci http://www.sciencemag.org/cgi/content/full/316/5827/998?ijke... There is a decent body of research and references behind it.