I note a recent article at the Harvard Business Review (with Cass Sunstein as one of the two authors) about group decision-making, and one of the passages that sticks out to me
The psychologists Roger Buehler, Dale Griffin, and Johanna Peetz have found, for example, that the planning fallacy is aggravated in groups. That is, groups are even more optimistic than individuals when estimating the time and resources necessary to complete a task; they focus on simple, trouble-free scenarios for their future endeavors. Similarly, Hal R. Arkes and Catherine Blumer have shown that groups are even more likely than individuals to escalate their commitment to a course of action that is failing—particularly if members identify strongly with the group. There is a clue here about why companies, states, and even nations often continue with doomed projects and plans. Groups have also been found to increase, rather than to lessen, reliance on the representativeness heuristic; to be more prone to overconfidence than individual members; and to be more influenced by framing effects.
With agents whose cognitive biases were not skewed toward wrong choices that are easy to justify to others, one might expect groups of such agents to have biases that are — for example, if you have a good "representative" to buttress your argument, you can explain your argument to others in a more effective way than if you could not, such that the group is more likely to reach a consensus around a decision supported by over-reliance on a representative than one that isn't. This is to say that one should naturally expect group decisions to be biased toward decisions that are easier to justify after the fact, and that this appears to involve an intensifying of the cognitive biases of individuals is evidence in favor of Mercier and Sperber's hypothesis.
* Human speech is primarily located in one hemisphere of the brain, though the other hemisphere can read and understand writing; human subjects whose hemispheres had been separated for medical reasons had, for the purposes of the experiment, written instructions shown to the non-speech hemisphere, whereupon they performed an action, whereupon the subject was asked why s/he had performed the action, and a perfectly confident and absolutely false answer was given.