Taxonomy and the hierarchy of life

Understand the idea

Classification arranges living things into groups by similarities and differences. Biologists have named more than 1.8 million kinds, and more wait to be found. Without a shared system we could not identify or talk about them clearly.

Aristotle made an early attempt. Carolus Linnaeus built the method still used to name species. Taxonomy (or systematics) is the study of those principles. Shared important features make a large group; smaller differences split that group again and again.

The ranks from largest to smallest are kingdom, phylum (or division in plants), class, order, family, genus, and species. A species is the smallest unit: members look alike in general and can mate to give fertile offspring. The scientific name has two parts: genus then species.

What to remember

• Taxonomy = principles of classification.
• Kingdom → phylum/division → class → order → family → genus → species.
• Species members can breed and produce fertile young.

Recap

We classify to name and group life. Learn Linnaeus, the seven ranks, and the two-part species name. That ladder is the map for the five kingdoms that follow.