Taxonomy
Created | Updated Jan 28, 2002
Why Classify?
Apparently the human condition has a built in
fascination with classification.
There are, however, many other compelling reasons to have a "universally" accepted classification system for all life as we know it. One of the most compelling is the need to communicate EXACTLY what organism is meant to people with other languages or common names for the organism. Leaving a clear record for posterity may also be simplified by a clear and planet-wide classification system. Another need is the ability to draw previously unseen similarities across organisms that might be grouped together for a different similarity.
How do we Classify?
Humans classify things in their minds every moment they are alive. The mind is a great pattern recognition device, and groups things of similar patterns together: Things To Eat, Things To Fear, Things To Drool over. These would all be informal classifications. Taxonomy is the formal classification of things (almost always referring to living organisms).
Classification in the past
Several people are responsible for how living things are currently classified. It may be impossible to recognize every scientist who left their mark on the system of classification but some of the biggies are:
Aristotle
He formed a system of classification around 300 BC. It was first based on whether the organism had red blood or didn't have red blood. He then subdivided organisms by physically observable characteristics. This would have been a hierarchal classification system. The idea of a hierarchal system is to start by making broad groups and then subdivide those groups into smaller groups repeating until you have small enough groups to easily handle.
Carolus Linnaeus (1707 - 1778)
A botanist who is considered the Father of Taxonomy for publishing Systema Naturae, a book that contained a classification system (and entries) for living things. His method of hierarchical classification is the base of today's taxonomy of living organisms. Although the structure of his system may be sound he often focused on a single common feature for relating species (such as reproductive organs of flowering plants).
John Ray(1628-1705)
The Father of Natural History, who started the practice of using total morphology to classify species rather than focus on one feature.
Current Classification System
Called Linnaean Taxonomy after Carolus Linnaeus, the hierarchy of classification is:
- Kingdom
- Phylum (or Division in Botanics)
- Class
- Order
- Family
- Genus
- Species
There are five Kingdoms in our current system:
- Animalia- over 1 million known species
- multicellular
- specialized eukaryotic cells1
- self-locomotion
- doesn't produce own food rely on ingestion
- Plantea- over 300,000 known species
- multicellular
- specialized eukaryotic cells
- NO self-locomotion
- produces own food
- Fungi- about 100,000 known species
- multicellular
- specialized eukaryotic cells
- doesn't produce own food rely on absorbtion
- Protista- about 100,000 known species
- single cellular
- eukaryotic cells
- Monera- about 10,000 known species (Often seperated into Eubacteria and Archaebacteria)
- single cellular
- prokaryotic cells2
When referencing a particular organism it is with the last two parts of the hierarchy (Genus and Species) that a unique name is made. This is called binomial (literally "two names") nomenclature. It is general pratice to italicize the Genus and Species, and often the Genus is abreviated to the first letter and capitalized. So that a wolf might be refered to as C. Lupus.
As more organisms were classified certain taxa became uncomfortably large. For instance, 75% of all living organisms are insects. This has led to the practice of having other groups between the levels of the hierarchy, such as subclass and superfamily. These in between levels allow scientists to group organisms in a way that may more easily show evolutionary significance.
The classification of humans:
- Kingdom: Animalia
- multicellular
- specialized eukaryotic cells
- self-locomotion
- doesn't produce own food
- Phylum: Chordata
- bilateral symmetry
- notochord3
- Subphylum: Vertebrata
- segmented spinal column
- central nervous system
- Class: Mammalia
- young nourished by milk
- specialized teeth
- endothermic (warm-blooded)
- Subclass: Theria
- give birth to live young
- Infraclass: Eutheria
- "true" Theria, meaning that live birth happens at an advanced stage
- Order: Primates
- opposable thumbs
- separate and well-developed radius and ulna in the forearm and tibia and fibula in the hindleg
- presence of a clavicle
- several other skeletal traits
- Suborder: Anthropoidea
- All higher primates: apes, monkeys, and humans
- Superfamily: Hominoidea
- apes and humans
- Family: Hominidae
- early man and modern humans
- Genus: Homo
- brain size
- complex tool making
- Species: Sapiens
- humans and sometimes direct ancestors who would be listed as a subspecies
Where did they get Whereus whatus?
When Linnaean Taxonomy was first started the common language of science (other than math) was Latin. A person naming a new species, generally the person who discovered it, would pick a Latin name having some relation to the species. Favorites include the name of the discoverer, the place it was discovered, obvious physical feature, and mythological references. Taxa other than species were generally a description of the morphological differences that defined that group.
The Future of Classification
Many people feel that our current classification system is woefully out of date, especially in light of our DNA sequencing technology. Other options do exist such as Cladistics and Gradistic Taxonomy4. However, moving the scientific community out of traditional practices has often gotten people burned at the stake. Perhaps in this information age the ease of interconnectivity will allow both systems to be used to the fullest extent.
1Eukaryotic: "true nucleus". Cells with a nuclear membrane2Prokaryotic: "before nucleus". Cells without a nuclear membrane3A dorsal rod (typically of cartilage or bone) that acts as support during locomotion4Also called Evolutionary Systematics
