How did scientists first classify living things?

Aristotle classified animals according to method of reproduction as did Linnaeus with plants. Both used a similar system as today with species, genus, and genera. Linnaeus was the more detailed and also used phylum and class.

Linnaeus had three Kingdoms: Animal, Vegetable, and Mineral.

Linnaeus' six animal classes were: Mammalia (mammals), Aves (birds), Amphibia (amphibians), Pisces (fish), Insecta (insects), and Vermes (no head). Linnaeus also had 26 vegetable classes.