The 2011 world series of poker is going on this week. The commentators observed that the vast majority of players are men. Among top-flight chess players there are relatively few women. When you look at similar activities among girls, such as the National Spelling bee (roughly middle school) or the Intel Science Talent Search (high school), there doesn't seem to be any such disparity. Does anyone have any idea why in the adult activity there is such a disparity, but not before? (The point of comparisons is that these are all competitions requiring brainpower, but not physical skills).