Early Biological Classification

Biologists have long recognized the need to classify living things. In fact, humans have been classifying living things for thousands of years. The earliest humans probably classified organisms as plants and animals. They may have further classified plants as edible or poisonous, and the animals as harmful or harmless. However, it was 300 BC before the first serious attempt was made to classify all the organisms known. This attempt was made by the Greek philosopher and scientist, Aristotle and his students.

Aristotle’s Classification System

Since only about 1000 kinds of organisms were known at that time, a very simple classification scheme could be used. Aristotle and his students first classified the organisms as plant or animal. They then classified the animals according to where they lived. This resulted in three groupings: air animals, water animals, and land animals. They classified the plants according to the structure of stems. Those with soft stems were called herbs; those with a single woody stem were called trees; and those with many small woody stems were called shrubs.

Aristotle’s classification system survived for almost two thousand years. However, by the beginning of the 18th century, over 10,000 kinds of organisms were known and Aristotle’s system was unable to classify them all. Many of newly discovered organisms would not fit into any category of Aristotle’s simple system. A new system was obviously needed.