In reviewing the studies surrounding these diverging approaches, Almécija and colleagues with expertise ranging from paleontology to functional morphology and phylogenetics discuss the limitations of relying exclusively on one of these opposing approaches to the hominin origins problem. "Top-down" studies sometimes ignore the reality that living apes (humans, chimpanzees, gorillas, orangutans, and hylobatids) are just the survivors of a much larger, and now mostly extinct, group. On the other hand, studies based on the "bottom-up"approach are prone to giving individual fossil apes an important evolutionary role that fits a preexisting narrative.