It’s said that history is written by the victors, but it would also be fair to say it typically isn’t written by people who are busy birthing, nursing or tending to babies, victorious though they may be. Such is the challenge faced by Sarah Knott, a historian who sets out to address that imbalance in Mother Is a Verb, her new book that blends memoir and history to tell a story of motherhood through the ages. As Knott describes in an informative note on her methods, traditional history has been summarized as the study of “Men in Public.” Here, under the subtitle An Unconventional History, are women in private.