Who among us hasn't marveled at the diversity and beauty of shells? Or picked one up, held it to our ear, and then gazed in wonder at its shape and hue? Many a lifelong shell collector has cut teeth (and toes) on the beaches of the Jersey Shore, the Outer Banks, or the coasts of Sanibel Island. Some have even dived to the depths of the ocean. But most of us are not familiar with the biological origin of shells, their role in explaining evolutionary...