The argument I've seen is that microlending works better when it's offered to women. Women are claimed (I haven't checked this) to be much more likely to put the money into supporting their families rather than spending it on personal consumption.
I have seen a study that supports this. One of the leading uses men made of money was throwing parties to show how well off they were.....
This is interesting, I wonder if there's anything to it: International variation in IQ – the role of parasites (paper) by Christopher Hassall of U. Carleton.
It strikes me as the sort of thing that could be as big an issue as lead in the environment. Raise the sanity waterline: improve health!