Classification, binomial naming & dichotomous keys

There are millions of different living things, so biologists need a tidy, agreed way to name them and sort them into groups. In this lesson we meet the binomial system — the two-word Latin name every organism is given, like Homo sapiens — and the rules for writing it. We build the hierarchical classification system, the nested ladder of groups from kingdom down to species, and see why a natural classification (one based on homologous features and shared ancestry) is better than an artificial one. We look hard at what the word species really means, using the biological, morphological, ecological and behavioural ideas. Finally we learn to build and use a dichotomous key — a chain of paired either/or questions that lets anyone name an unfamiliar organism.