Why we classify
Classification is the placing of organisms into groups based on shared features. Organisms are grouped so that they can be studied and identified more easily, and the groups reflect how closely related the organisms are. Traditionally organisms were classified using shared morphology (outward form) and anatomy (internal structure); today scientists also compare DNA base sequences, giving more accurate, evidence-based groupings.
Key idea
The main groups, from largest to smallest, are: Kingdom → Phylum → Class → Order → Family → Genus → Species. A species is a group of organisms that can reproduce to produce fertile offspring.
The binomial system
Every species is given a two-part Latin name – the binomial system, devised by Carl Linnaeus. The first part is the genus (capital letter); the second is the species (small letter). The whole name is printed in italics or underlined when handwritten.
Worked example
Humans are named Homo sapiens. Homo is the genus and sapiens is the species. Note the capital H, the small s, and the whole name in italics. Writing “Homo Sapiens” or “homo sapiens” would lose marks.
Remember
- Genus first with a capital; species second with a small letter.
- Species sharing a genus are closely related.
- DNA sequence comparison gives the most reliable modern classification.