There are millions of species on our planet. Although species can be very different from each other, many have similar features that allow us to put them into groups. This is called classification.
The first big division of living things in the classification system is to put them into one of five kingdoms. These are based on what an organism's cells are like.
The five kingdoms are:
Living things can then be ranked according to:
The binomial system of naming species uses Latin words. Each name has two parts, the genus and the species. For example, human beings belong to the genus Homo, and our species is sapiens - so the scientific name is Homo sapiens.
The binomial system is important because it allows scientists to accurately identify individual species. For example, the European robin is Erithacus rubecula. It is much smaller than the American robin, Turdus migratorius, which belongs to a different genus.
Cladistics is another way to classify organisms. It can use data from DNA or RNA sequences, rather than just physical characteristics. It emphasises the evolutionary relationships between different species.