Introduction: When paleontologists discover fossils, they determine whether they have discovered fossils of recent or early organisms. They then determine the kinds of organisms the fossils represent. If a skull were discovered and determined to be a primate skull, the next step would be to determine whether it is of an ape or a human. Because evolutionary change has occurred in both groups, the skull could be of early or modern ape or early or modern human. Because humans and apes evolved along separate lines, certain physical characteristics can be used in an attempt to classify the fossil skull as belonging to either ape (early or modern), early human, or modern human. Techniques similar to the one used in this investigation are used by anthropologists, paleontologists, and archeologists.