IGCSE Biology - 1.2 Concept and uses of classification systems

Objective: Explain that classification systems aim to reflect evolutionary relationships.

What is a Classification System?

A classification system, also known as taxonomy, is a way of organizing and grouping organisms based on shared characteristics. It helps us understand the diversity of life on Earth and the relationships between different species.

Why do we use Classification Systems?

Classification systems are essential for several reasons:

• Organization: They provide a logical framework for organizing the vast number of species.
• Communication: They allow scientists worldwide to communicate clearly about specific organisms using a standardized naming system.
• Prediction: Understanding the classification of an organism can help us predict its characteristics and behavior.
• Evolutionary Relationships: Modern classification systems are designed to reflect the evolutionary history of organisms.

Evolutionary Relationships and Classification

The primary aim of modern classification systems is to reflect the evolutionary relationships between organisms. This means grouping organisms together based on how closely they are related through common ancestors. Organisms that share more recent common ancestors are classified together.

This concept is often represented as a phylogenetic tree or evolutionary tree. These trees show the branching patterns of evolutionary lineages.

Levels of Classification

Classification systems use a hierarchical system of categories, from broad to specific. The main levels of classification, from broadest to most specific, are:

1. Domain
2. Kingdom
3. Phylum (Division - used in plants)
4. Class
5. Order
6. Family
7. Genus
8. Species

Example of a Classification

Consider the classification of humans:

Level	Classification
Domain	Eukarya
Kingdom	Animalia
Phylum	Chordata
Class	Mammalia
Order	Primates
Family	Hominidae
Genus	Homo
Species	Homo sapiens

This classification shows that humans are closely related to other primates, such as chimpanzees and gorillas, because we share a more recent common ancestor with them than with, for example, insects.