Development of Classification Systems

In the 20th century, technological advancements have improved biological classification. This is because scientists have gained a better understanding of:

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• The study of internal structures using microscopes

• Biochemical processes that take place inside cells

• Genetics, such as the sequencing of genomes

As microscopes have developed, scientists can distinguish structures within cells, allowing them to take a more scientific approach to classification.

By comparing DNA sequences in different species, scientists can tell how closely related they are. Research into DNA sequences shows that with closely related species, there are fewer differences within the DNA sequences.

Three-Domain System

In the late 20th century, Carl Woese used evidence from chemical analysis to develop the three-domain system. In this system, all organisms are organised into one of three domains:

• Archaea – Single-celled organisms often found in extreme environments, such as hot springs and salt lakes

• Bacteria – True bacteria

• Eukaryota – Animals, plants, fungi and protists

These domains are divided further into smaller groups: kingdom, phylum, class, order, family, genus and species. Woese found that archaea significantly differ from bacteria, so they should have their own separate domain.