I will review recent research in neuroimaging and computation neuroscience, and present a new paradigm for studying decision making in pairs. Results from this paradigm demonstrate that discussion between the partners is necessary and sufficient for creating an advantage for the group decision and a more accurate picture of the world than can be achieved by either partner alone. I conclude that metacognition - the ability to introspect upon one's own experience and to communicate this to another - is the key to understanding the evolution of human cognition, including consciousness and group decision making. Presented by Chris Frith (Wellcome Trust Centre for Neuroimaging at UCL, UK) Creative Commons Attribution-Non-Commercial-Share Alike 2.0 UK: England & Wales; http://creativecommons.org/licenses/by-nc-sa/2.0/uk/