How Can We Classify the Enormous Biodiversity of Our Planet?

Traditional Classification Systems

• The classification of biodiversity traditionally involves kingdoms and, more recently, domains. Kingdoms group living beings by evolutionary relationships, while domains categorize them based on cellular characteristics.

• An example illustrates this: species with a common ancestor show shared traits (e.g., furry tails in certain groups), indicating closer evolutionary ties compared to others.

Historical Context of Classification

• Aristotle's early classification divided life into plants, animals, and humans. This system persisted for centuries until new species were discovered during the 16th and 17th centuries.

• In the 18th century, Carl Linnaeus developed a modern classification system. He published works in 1753 for plants and in 1758 for animals, introducing humans into the animal kingdom.

• Linnaeus categorized organisms into broad categories (kingdom, genus, species), establishing foundational taxonomic principles and creating binomial nomenclature still used today.

Evolution of Taxonomy

• Haeckel proposed a new kingdom called Protista in 1866 to classify simpler organisms distinct from plants and animals; bacteria were included within this realm.

• In 1925, Chatton differentiated living beings based on cellular structure into two major groups: prokaryotes and eukaryotes.

Introduction of New Kingdoms

• Copland introduced the Monera kingdom in 1956 to separate prokaryotes from protists. Monera was limited to bacteria due to their unique characteristics.

• Whitaker's five-kingdom classification in 1969 established Fungi as its own kingdom (including mushrooms, molds, and yeasts), separating it from Plantae.

Modern Taxonomic Revisions

• The five kingdoms are widely accepted today; however, Protoctista (now Protista) and Monera have undergone revisions due to their diverse nature.

• The Protista kingdom is often seen as a "catch-all" category for eukaryotic organisms that do not fit neatly into other kingdoms due to their polyphyletic origins.

Advances in Domain Classification

• The Monera kingdom includes two distinct prokaryotic groups: archaea (or archaeobacteria) and bacteria (or eubacteria).

• A higher taxonomic category called "domain" was established above kingdoms. Three domains emerged: Archaea, Bacteria, and Eukarya.

Recent Developments in Taxonomy

• In 1990, Woese proposed classifying life forms into three domains based on genetic data tracing back billions of years to a common ancestor known as progenote or produbionte.