A new study from the American Society of Plastic Surgeons suggests that marital stress, smoking, and heavy drinking disproportionately affect women's hair loss. The study, conducted on 42 sets of female identical twins, found that the major predictor of female hair loss was divorce or widowhood, but that heavy drinking and smoking also contributed significantly. In contrast, the primary predictor for male hair loss is genetics, followed by smoking, sun exposure, and dandruff.
Female hair loss, then, would appear to be driven far more by physical and emotional stress than genes. Interestingly, we know that marital stress like divorce does have plenty of other negative effects for men, including shortened lifespans. So if you want a full head of hair well into old age, don't smoke, drink moderately, and stay single.