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Taxonomy and Scientific Classification
The science of taxonomy classifies species into evolutionary relationships to help identify organisms and name species. Taxonomy is also referred to as scientific classification.
Today's classification system was developed by Carl Linnaeus as an important tool for use in the study of biology and for use in the protection of biodiversity. Without very specific classification information and a naming system to identify species' relationships, scientists would be limited in attempts to accurately describe the relationships among species. Understanding these relationships helps predict how ecosystems can be altered by human or natural factors.
Preserving biodiversity is facilitated by taxonomy. Species data can be better analyzed to determine the number of different species in a community and to determine how they might be affected by environmental stresses. Family, or phylogenetic, trees for species help predict environmental impacts on individual species and their relatives.
Linnaean Taxonomic System
Carl Linnaeus was born in 1707 and died in 1778. He created the entire category of systematic zoology and botany as well as a classification scheme—still used by biologists today. His masterpiece was the Systema Naturae. Linnaeus invented the classification system to establish consensus on plant and animal names and to understand complex evolutionary relationships between organisms. The Linnaean taxonomic system begins with the most general category of Domain or Kingdom and becomes increasingly specific until it ends with a specific genus and species name derived from Greek and/or Latin roots.
Based on concepts introduced by his scientist predecessors, Linnaeus developed his system so that each species had a Latin double name. The first name is the genus and the second is the species name. This two-word naming system is called binomial nomenclature. The name is always italicized with the genus capitalized and the species in lowercase letters.
| Kingdom | Animalia |
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Phylum | Chordata |
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Class | Mammalia |
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Order | Primates |
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Family | Hominidae |
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Genus | Homo |
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Species | sapien | ||
There are 8 general taxonomic groupings, starting with the most general and ending at the most specific. The groupings are: Domain, Kingdom, Phylum (or Division for plants), Class, Order, Family, Genus and Species. In some cases, subgroups are included for accuracy such as subclass, superorder, suborder, and infraorder to name a few. The naming of life can become incredibly complex. When the species grouping is not specific enough, subspecies categories are added. Domains are also sometimes added above the kingdom level, if a high level of generality is needed. On the other hand, if more detail is needed, tribes can be added between family and genus categories and sections or series can be added between genus and species categories.
The five Kingdoms are Monera, Protista, Fungi, Plantae, and Animalia. Under each Kingdom, Phylums are listed and under each Phylum there are many Classes (and so on). With over 10,000 species, Kingdom Monera consists of unicellular bacteria and cyanobacteria. Kingdom Monera is also the only kingdom made up of prokaryotic cells or cells without nuclei and organelles not surrounded by a membrane. The other four kingdoms consist of eukaryotes or cells with nuclei and organelles bound by a membrane. Kingdom Protista consists of 250,000 species of single celled protozoans and macroscopic algae. There are 100,000 species in Kingdom Fungi and they are usually either heterotrophic haploid or dikaryotic cells. There are 250,000 species in Kingdom Plantae and they all are autotrophic forms of plants that keep the embryo on the female part of the plant. With over 1,000,000 species, Kingdom Animalia consists of multicellular animals that lack a cell wall (plant cells have a rigid cell wall) and form a blastula early in life.
To demonstrate how an organism is classified, let us use the classification of the commonly named “the blue whale”. The information provided by this common name is not enough to put the whale into any evolutionary relationship with other organisms. Scientists however, call the blue whale by its scientific name—Balaenoptera musculus. An example of how scientists would classify and name a blue whale is as follows:
• All whales are animals because they have more than one cell, eat food and originate from a fertilized egg—so they first are categorized into the most general category—Kingdom Animalia.
• Whales are placed into the Phylum Chordata (the category below Kingdom) because they have a spinal cord and gill pouches. In fact, humans are also in Phylum Chordata.
• Because they are warm-blooded, produce milk for their young and have a heart with four chambers, whales are in the Class Mammalia.
• At the “Order” category, whales begin to be distinguished from humans and other land mammals. Whales are classified as cetaceans because they live in the water all year round. The suborder is Mysticeti due to the baleen plates in the mouths of whales, helping them to filter in food.
• Blue whales have folds around their throat that expand to take in large volumes of water when feeding. Because not all whales have this characteristic, blue whales are placed into the Family “Balaenidae”.
• Within the Family is another group of species more immediately related to each other. The “Genus” for blue whales is Balaenoptera.
• The definition of a species includes many factors, especially the requirement that individuals must be able to successfully breed with each other. The species name for blue whales is musculus, meaning that in addition to other common traits, whales of the species musculus are able to breed with each other and provide viable (living) offspring. The final scientific name is Balaenoptera musculus with the genus capitalized and the species name in lower case letters and both italicized.
Phylogenetic Trees
A phylogenetic tree is similar to a family tree except that it shows evolutionary relationships between species rather than relationships between individuals. Phylogenetic trees contain a lot of information and can reveal how far back in time a species began, along with the most recent common ancestors between species. DNA analysis is used to provide information to support the construction of phylogenetic trees. Every “node” on a phylogenetic tree is referred to as a taxonomic unit and represents a common ancestor. Scientists can zoom in on a particular part of a phylogenetic tree, omitting the “root” of the tree in order to focus on a particular segment. A rooted tree is simply the bigger, zoomed-out picture.
The Science of Classification
Taxonomists are responsible for the discovery of new species, analysis and compilation of collected data, and the release of new information to the public, including other scientists. The research requires valuable identification skills, the ability to categorize and recognize species relationships, an understanding of ecosystems and ecology, knowledge of species distribution, and the ability to determine keystone species. They must also be able to submit data and explain the synthesis clearly for people in communities.
Scientists have relied on Linnaeus's system of classification for the last two hundred years. After Darwin’s time, it became clear that another dimension could be added to the phylogenetic tree so taxonomic groups would represent the principle of common descent. Related taxa (or categories) were moved to occupy what can be visualized as a bunch of leaves on a particular branch. These relatively new and helpful groupings are referred to as monophyletic groups.
A new development in taxonomy is the revelation that using a cladogram can make it easier to view evolutionary relationships. A cladogram is basically an isolated branch of the phylogenetic tree turned sideways with each line indicating the amount of time between the ancestor and the species. Each “clade” represents a monophyletic group. Because it is only a short branch of the entire tree it is not usually necessary to refer to the more general Linnaean form of classification.
Taxonomy is becoming more important as scientists struggle to identify species in order to understand the subtle relationships and complex reactions of ecosystems threatened by human pursuits. The study of taxonomy provides a solid foundation for the research needed for the conservation of marine life.
Sources:
» Scientific Classification - U.S. Department of Commerce/NOAA/NMFS/AFSC/NMML
» Marine Taxonomy in the New Millennium - Discussion Paper for the Oceans Policy Science Advisory Group, Prepared by the Australian Marine Sciences Association (AMSA)
» Wikipedia: Scientific classification
» Wikipedia: Phylogenetic tree
» The Five Kingdoms Of Life, The Amazing Diversity Of Living Systems - Wayne's Word Gee-Whiz Trivia For February 1998
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