1. Aristotle classified life into 14 groups (e.g., mammals, birds, etc.), and subdivided them by size.
2. Ray grouped animals and plants according to how he thought they were related.
3. Linnaeus grouped plants by flower parts; his categories were published in Systema Naturae in 1735
4. Today, taxonomists use seven categories of classification: species, genus, family, order, class, phylum, and kingdom.
a. A higher category, the domain, has recently been added to these seven categories.
b. The higher the category, the more inclusive it is.
c. Members of a kingdom share general characters; members of a species share quite specific characters.
d. Since one taxonomic group exists inside another group, these categories are also termed nested.
A character is any structural, chromosomal, or molecular feature that distinguishes one group from another.
e. Additional levels of classification can be added by adding super , sub , or infra (e.g., suborder); thus, there are more than 30 categories of classification.