Discuss the fact that classification systems were based originally on observable features but that more recent approaches draw on a wider range of evidence to clarify relationships between organisms, including molecular evidence. Early classification systems simply used observable features to put organisms into groups, but this is problematic because the fact that some organisms look similar doesnt mean theyre closely related, e.g. sharks and whales look similar and live in the sea, but sharks are fish and whales are mammals! Classification systems today are based on more evidence, like: Molecular evidence protein and DNA similarities, e.g. how its stored, closeness of bases. Anatomical Similarities in structure and function of body parts Behavioural evidence Similarities in behavior and social organization of organisms Compare and contrast the five kingdom and three domain classification systems.