Sex and Handwriting

I was doing some grading and TheWife was looking over my shoulder. Without looking at the names, she was able to correctly determine the sex of the writer in 29 out of 30 cases. While she is quite a detail-oriented person, my guess is that this experiment could be successfully repeated with most people. If anyone can, in the majority of cases, pick out male from female handwriting, what accounts for the difference, nature or nurture?