"Butterflies" also allude to the idea that even a flower's petal falling on the ground or, in this case, a gentle flutter of wing, can have a profound impact on the universe.  Allende dramatizes the heroic possibilities of the ordinary, of the seemingly obscure, which is the traditional way many would have viewed women in the Dominican Republic during the time of the events in the novel. Science speaks of an idea called the butterfly effect that argues "a butterfly's wings might create tiny changes in the atmosphere that ultimately cause a tornado to appear (or prevent a tornado from appearing). The flapping wing represents a small change in the initial condition of the system, which causes a chain of events leading to large-scale phenomena. Had the butterfly not flapped its wings, the trajectory of the system might have been vastly different."  Such might be said of the apparently ordinary lives of these very heroic women.

Butterflies are the beautiful yet remarkably strong, tenacious creatures who, despite their outward fragility, are capable of remarkable feats. Butterflies can travel hundreds of miles, a seemingly impossible ability given their apparent delicateness; likewise, the very feminie Mirabal sisters are able to withstand challenges to their lives few could match.

Not many creatures on earth can maintain such a veneer of fragility but possess such interior strength.  Like butterflies, the accomplishments of these remarkable women seem "impossible for us, ordinary men and women" (from the postcript, page 324).