Scholars have long argued that the developmental state of the human infant at birth is unique. This volume expands that argument, pointing out that many distinctively human characteristics can be traced to the fact that we give birth to infants who are highly dependent on others and who learn how to be human while their brains are experiencing growth unlike that seen in other primates. The contributors to this volume propose that the "helpless infant" has played a role in human evolution equal in importance to those of "man the hunter" and "woman the gatherer." The authors take a broad look at how human infants are similar to and different from the infants of other species, at how our babies have constrained our evolution over the past six million years, and at how they continue to shape the ways we live today.