My Most Absurd Belief
By Arnold Kling
is that human nature has changed in the last few hundred years. If you could go back to 1708 and replace all of the babies at conception with babies conceived today, my prediction is that the alternative history from 1708 to 2008 would have less violence, more economic growth, and faster scientific progress. Conversely, if you were to replace babies being conceived today with babies conceived in 1708, they would grow up to produce staggering increases in crime and violence, along with severe economic decline.
I take the Flynn effect to be a true indicator that intelligence has gone up over the past few generations. Even if nothing else in human nature has changed, the IQ difference would produce the results I predict in the thought experiment. But other parts of human nature probably have changed as well.
Tyler Cowen is into this question of what is your most absurd belief. It means a belief to which you assign a much higher probability of truth than would other intelligent truth-seekers.