Biological classification organizes all life on Earth and allows scientists to study relationships between organisms and build evolutionary trees. The system, developed by Linnaeus, divides organisms into domains, kingdoms, phyla, classes, orders, families, genera, and species. Humans, for example, are in the Eukaryota domain, Animalia kingdom, Chordata phylum, Mammalia class, Primates order, and Hominidae family, with the scientific name Homo sapiens sapiens. Each taxonomic rank reveals more information about an organism.
Biological classification is a system used to organize and codify all life on Earth. There are a number of goals to biological classification, beyond the obvious need to be able to accurately describe organisms. Creating a classification system allows scientists to examine the relationships between various organisms and build evolutionary trees to explore the origins of life on Earth and the relationship of modern organisms to historical examples. You may also hear biological classification referred to as “taxonomy.”
Humans have been giving names to organisms for a long time and have been trying to organize life on Earth into understandable categories for nearly as long. A variety of systems have been developed at various times, with various drawbacks and bonuses. The biological classification system used today was developed by Linnaeus, an 18th-century scientist, although it has been extensively refined over the centuries to reflect new information in the sciences.
The biological classification system divides organisms into a variety of taxonomic categories or ranks, starting with domains, the highest order of life. There are three domains: Eukaryota, Eubacteria and Archaea. After the domains are the kingdoms, which are further divided into phyla, classes, orders, families, genera and species. The development of higher order domains is relatively recent compared to the rest of taxonomic classifications and not all scientists agree on or use the domains in biological classification. You can also see subsets of these basic grades that are used to distinguish subtle differences.
All organisms can be coded using biological classification. Organisms are related to each other by similarities and separated by differences which are highlighted by the plethora of options at each taxonomic rank. Using a specific epithet or scientific name that includes the formal terms for genus and species also ensures that people know exactly which organism is under discussion.
To illustrate how taxonomic classification works, it may be helpful to distinguish the biological classification of a well-known organism: humans. Working from the top down, humans are in the Eukaryota domain and the Animalia kingdom, which places them with other multicellular eukaryotic organisms from cats to cows. The human phylum is Chordata, indicating that they possess an anatomical structure called a notochord during the early stages of their development, and are in the class Mammalia, along with other animals that give birth to live young and suckle their young with milk.
Humans are in the order of primates, placing them in a large group of animals with similar biological adaptations, and the family Hominidae, along with chimpanzees, gorillas, and orangutans. The scientific epithet for man, Homo sapiens sapiens, includes genus and species, as with all organisms, along with a subspecies. The use of a subspecies distinguishes between humans who are genetically distinct enough to be different, but are still capable of interbreeding. Other subspecies of humans are now extinct, but archaeological evidence suggests that multiple subspecies may have coexisted at some point in history.
For people who are knowledgeable about the biological classification and properties of each taxonomic rank, each step lower on the taxonomic ranking ladder reveals more information about humans. Only by hearing that humans are in the Eukaryota domain, for example, does a scientist know that humans have a cellular structure that includes specialized structures, including a cell nucleus, within a protective membrane.
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