I believe the full paper that this article is based on can be found here: http://www.sciencemag.org/content/334/6062/1518.full http://www.sciencemag.org/conten

I believe the full paper that this article is based on can be found here: http://www.sciencemag.org/content/334/6062/1518.full http://www.sciencemag.org/content/334/6062/1518.full