The 9+ month marathon: How pregnancy may have shaped human endurance capacities

Anthropology has long considered the evolution of our uniquely human endurance capacities to be the result of selection upon anatomical and physiological features imposed by the demands of thermoregulation and resource acquisition, particularly during the demands of persistence hunting. Research has focused on the anatomical changes present in our hominin lineage that would have improved endurance economy, and, therefore, our capacity for persistence hunting. However, little work has been done to understand the origins of endurance physiology. Here, I suggest our uniquely human endurance capacities are an exaptation of underlying pregnancy physiology. I review the physiological changes associated with endurance training followed by the changes associated with pregnancy, highlighting the similarities between the two. I then argue that the evolution of bipedalism created a situation in which pregnancy physiology could be exaptated for endurance running abilities. I then present three different possibilities for when and how this exaptation may have come about and how this hypothesis can be tested in the future. Expanding our questions and hypotheses for the origins of human endurance capacities to include an intentional examination of female and pregnancy physiology will provide unique insights into our evolutionary trajectory.