Basic Taxonomic Concepts

Basic Taxonomic Concepts

• Taxonomy is the science of organizing and categorizing living organisms into classes called taxa.
• Systematics is the study of the diversification of life forms over time, including their relationships.
• Systematists and taxonomists both provide scientific names, detailed descriptions, and classify organisms. However, systematists also investigate evolutionary histories and consider environmental adaptation.
• Carl Linnaeus, a Swedish botanist, is known as the "father of taxonomy."
• In 1735, Linnaeus published Systema Naturae ("System of Nature").
• Linnaeus' classification system, which is still used today, has seven levels: Kingdom, Phylum, Class, Order, Family, Genus, and Species.
•  Each level gets increasingly specific from kingdom to species.
• Binomial nomenclature is a two-part scientific naming system.
• The first part is the genus (e.g., Homo), and the second part is the species descriptor (e.g., sapiens).

Three Domain System

• Scientists classify all living organisms based on three domains: Bacteria, Archaea, and Eukarya.
• Bacteria are unicellular, prokaryotic organisms found everywhere.
• Archaea are unicellular, prokaryotic organisms that thrive in extreme environments (e.g., hot springs).
• Eukarya include organisms with a nucleus in their cells.

Eukarya Kingdoms

• Eukarya are divided into four kingdoms: Protists, Fungi, Plants, and Animals.
• Protists include organisms diverse in form and function, which may be classified as plant-like, animal-like, or fungus-like.
• Fungi are heterotrophic, multicellular organisms that feed on dead organisms.
• Plants are autotrophic, multicellular organisms that produce their own food through photosynthesis.
• Animals are heterotrophic, multicellular organisms that move.

Classification Based on Evolutionary Relationships

• Modern classification is based on evolutionary relationships.
• Phylogeny is the study of relationships and their evolutionary development among different groups of organisms.
• A phylogeny is commonly represented by a phylogenetic tree.
• Cladistics is a common method to make evolutionary trees, which places species in order of descent from a common ancestor.
• Clades are identified by snipping branches under a node.
• Clades represent a group of organisms that are derived from a common ancestor.
• Nodes represent the most recent common ancestor of a clade.
• Derived characters are traits shared in different degrees by clade members.
• A cladogram is an evolutionary tree made using cladistics.

Limitations of Phylogenetic Trees

• Closely related species may not always look alike.
• Phylogenetic tree branches usually do not account for length of time and only depict evolutionary order.
• The evolution of one organism does not necessarily imply the evolutionary end of another.

Summary

• To build phylogenetic trees, scientists collect accurate information about organisms (morphological and molecular data) to find connections between them.
• Similarities between organisms can stem from shared evolutionary histories (homologies) or separate evolutionary paths (analogies).
• Scientists use cladistics to organize events resulting from shared characteristics, to create an evolutionary timeline.
• The principle of maximum parsimony is often applied. This means that events likely occurred in the most simple and obvious way, with the least number of major divergences.