Why men lawyers earn more than women

I just saw on ssrn.com this abstract for a paper that explores that question. Here's the abstract:

Using a dataset of survey responses from University of Michigan Law School graduates from the classes of 1970 through 1996, I find that fathers tend to receive higher salaries than non-fathers (a "daddy bonus"). In addition, mothers earn less than non-mothers (a "mommy penalty"). There is also some statistical support for the inference that there is a penalty associated purely with gender (women earning less than men, independent of parenthood), another result that is unique to the literature.

Analyzing full- or part-time status as well as work hours also suggests a key difference between women and men. Those who take part-time status are almost entirely women who take on child-rearing duties, and they reduce their work hours by an average of approximately thirty percent. These statistical results are, however, significantly less reliable because of the very small numbers of respondents (male or female) who work less than full time.

You can download the full paper, by Neil H. Buchanan, here.