U-shaped developmental functions, and their N-shaped cousins, have intrigued developmental psychologists for decades because they provide a compelling demonstration that development does not always entail a monotonic increase across age in a single underlying ability. Instead, the causes of development are much more complex. Indeed, well-documented U-shaped developmental functions have often led to a re-evaluation of theory and/or a questioning of underlying assumptions. U-shaped developmental functions are evident in much of the authors' own work as well, and they too do not view them as implying loss or regression. It was tempting for the authors to end their commentary with a summary statement about how U-shaped developmental functions do not constitute loss, but instead reveal complex "reorganizations" that likely reflect the operation of a number of developmental forces, including a reconstruct of the same information that the infant has been perceiving all along. But they felt such an ending might prematurely close what should still be an open area of investigation.