Abstract
Since they were first recognized as remains of once-living creatures, fossils have captivated our imagination. In his book On the Origin of Species (1859), Charles Darwin devoted two chapters to one of his most vexing concerns-gaps in the fossil record. From Darwin's day to the present, the completeness of the fossil record (or lack thereof) has remained a centerpiece in the debate over origins. What were Darwin's concerns, and where do we stand 150 years later?