There is a hidden bias in the sex data, one that has never been discussed, perhaps because it has not been recognized. I am not referring to the “biological bias” that was created when ancient events put the sexes on different evolutionary paths, altering the way future generations of men and women would talk, for that is a central issue of the book. Nor am I referring to the “gender bias” of researchers who may have secretly hoped to show that one sex is superior to the other. A century ago, Helen Thompson Woolley thought that no area of science could equal gender studies when it came to “flagrant personal bias, logic martyred in the cause of supporting a prejudice, unfounded assertions, and even sentimental rot and drivel.”

The bias that I have in mind relates to neither of these things, though it may lie somewhere in between human evolution and the practice of science. For it involves the subtle ways our ancestors continue from the grave, as it were, to influence the investigation of women and men???s speech today.