Chapter1: Classification

Aristotle’s System

Image from: Wikipedia Commons

Aristotle was not the first observer and classifier of nature, but he was the first to systematically record a methodology for doing so.   He was a great observer of nature, and he formally described and classified hundreds of species. The system he established was based on obvious and visible physical features.  He classified things as either plants (which were green and did not move) or animals (which did move.) He further classified animals by where they lived (land, sea, and air.)   Aristotle further classified animals as ‘with blood’ and ‘without blood’. Animals with blood were divided into live-bearing (humans and mammals), and egg-bearing (birds and fish). Invertebrates (‘animals without blood’) are insects, crustacea, and mollusks. It was a simple system but he was quick to admit it. – “Mine is the first step and therefore a small one, though worked out with much thought and hard labor. You, my readers or hearers of my lectures, if you think I have done as much as can fairly be expected of an initial start. . . will acknowledge what I have achieved and will pardon what I have left for others to accomplish. To read more, or to see the source of this quote, click here.

The Linean System

Swedish naturalist Carolus Linnaeus established clear rules for a two-name system called the binomial system of nomenclature. His Systema Naturae (1735), established the standard of taxonomy that is largely still in use today. Linneaus, whose real name was Carl Linne, was obsessed with classifying and organizing species. Nonetheless his obsession, and indeed his genius, has survived the test of time. With Binomial Nomenclature, similar organisms are grouped into a genus, and each is given a two-word Latin name.  The first word of this name is the genus name, and the second word describes the organism, where it’s from, or it identifies the person who discovered it.  This system circumvents the problem of species with multiple common names in multiple languages. Scientists could now refer to each species by one specific Latin name. To read more about the life and work of Linnaeus, click here.

Two examples of the Linean System of Classification

Mr. Van Arsdale (Homo sapiens) holding a Oncorhynchus kisutch

Pacific White Sided Dolphin, Lagenorhynchus obliquidens, image from Wikipedia

Common name – humans Common name – pacific white-sided dolphin
KINGDOM – Animalia KINGDOM – Animalia
PHYLUM – Chordata PHYLUM – Chordata
CLASS – Mammalia CLASS – Mammalia
ORDER – Primates ORDER – Cetacea
FAMILY – Hominidae FAMILY – Delphinidae
GENUS – Homo GENUS – Lagenorynchus
SPECIES – Homo sapiens SPECIES – Lagenorynchus obliquidens

Three Domains

Biological classification today is based as much on genetic analysis and evolutionary history as it is physical form. Nature is never as black and white as we would like it to be, and some species or groups are very difficult to place in just one group as we have defined them. Hence, the science of biological classification needs to be constantly re-evaluated in the face of new or noteworthy data. Currently, we classify all living things into three large domains based on the structures of their cells and six kingdoms based on other features. It is likely that the near future will bring a reclassification of species into eight or nine kingdoms.

The Six Kingdom System

Kingdom Monera [10,000 species]:

  • Unicellular and colonial–including the true bacteria (eubacteria) and cyanobacteria (blue-green algae).
  • No organelles or nucleus
  • Can be autotrophs (photosynthetic) or heterotrophs (eaters)
  • More information on Monera

Kigdom Archaea [unknown number]

  • Unicellular
  • No organelles or nucleus
  • Have a distinctively different biochemistry that makes them different from Monera
  • Initially, Archaea were seen as extreme bacteria that lived in harsh environments (such as hot springs and salt lakes), but they have since been found in a broad range of habitats, such as soils, oceans, and marshlands.
  • More information on Archea

Kingdom Fungi [100,000 species]:

  • Dominated by a haploid life cycle
  • Multicellular
  • Most have cell walls containing chiton
  • Generally heterotrophic although many could be considered parasitic
  • Includes yeasts, mushrooms, molds, lichens, and a host of other organisms
  • More information on Fungi

Kingdom Plantae [250,000 species]:

  • An alternation of haploid and diploid life cycles
  • Mostly autotrophic
  • Non-mobile
  • All multicellular with specialized tissues
  • All have cell walls containing cellulose
  • Not all green.  Plants may use a variety of pigments to absorb the sun’s rays.
  • More information on Plantae

Kingdom Animalia [1,000,000 species]:

Build Your Own Classification

Procedure: 

  1. Using the fabulous website onezoom.org, search for your favorite species, find out its scientific name, and begin to explore its classification.
  2. Use the link to that species Wikipedia page to identify the organism’s genus, family, class, order, phylum, and kingdom as well as other organisms contained within those groups.
  3. Build an infographic that displays the classification of your favorite species along with a number of its relatives. Include the names of other organisms (both common and scientific names) that belong to each of the groups from number three above.
  4. At each ascending classification level, add to your infographic two other species from its genus, three from the family, four from the order, five from the class, six from the phylum, and seven from the kingdom. If there are no other members of the genus or family shift up, but you should still have at least 25 related species.
  5. At each level, describe one characteristic that links the members of this group together (i.e. all mammals have hair and produce milk from mammary glands.)
  6. At least one species from each level of classification should be accompanied by an image or video.  Besides onezoom.orgArkive.org is a great source for images.
  7. All of these species should be visually and taxonomically organized in a way that is aesthetically pleasing and easy to follow.
  8. Here is a rubric for how you will be graded.