Classification

What is Classification The grouping of objects or organisms based on a set of criteria. Scientist use classification as a way to communicate and retain information about organisms. Grouping organisms in classification methods makes this easier.

Aristotle Greek Philosopher Developed the first accepted system of biological classification. Classified organism as either plant or animal Classified animals further by grouping them based on the presence or absence of “red blood”. Classified plants further by grouping them based on size and structure(tree, shrub, herb).

Aristotle’s Classification Limitations Based on his view that species are distinct, separate and unchanging. We now know that species change. Aristotle’s system did not account for evolutionary relationships. Many organisms do not fit easily into this system.

Linnaeus Swedish Naturalist Took Aristotle’s classification method and formalized it into a scientific system. Based his system on observational studies of the morphology and the behavior of organisms. First system of taxonomic organization. Taxonomy: identifying, naming, and classifying species based on natural relationships.

Binomial Nomenclature Linnaeus’s method of naming organisms. Uses Latin to give each species a scientific name that has two parts. First part of the name is the Genus name Second part of the name is the species name.

Rule for Naming Species in Binomial nomenclature The first letter of the genus name is always capitalized but the rest is lower case. The species name is written in lower case letters as well. If the name is written in a book it should be italicized. When a scientific name is hand written both parts are underlined.

Examples of Binomial Nomenclature. Cardinalis cardinalis Rosa rugosa Canis lupus

Modern Classification System Uses Linnaeus’s classification system but have been modified to reflect evolutionary ancestry. Scientist today use Eight categories to identify species. The modern classification system starts with domain and then goes all the way down to species.

Modern Classification Taxonomic System There are eight taxa that the modern classification system uses to organize species. These taxa range from having broad characteristics to having very specific characteristics. Domain Order Kingdom Family Phylum Genus Class Species

Three Domains Domain is the broadest taxa and a domain can contain one or more kingdoms Three Domains Bacteria Archaea Eukarya

3 ways of determining a species Typological species concept: classification is determined by the comparison of physical characteristics with a type specimen. Type specimen: an individual of the species that best displays the characteristics of the species.

2. Biological species concept: classification is determined by similar characteristics and the ability to interbreed and produce fertile offspring. Most used concept, still used today. 3. Phylogenetic species concept: classification is determined by evolutionary history.  Phylogeny—the evolutionary history of a species.

Evidence used to determine Phylogeny Use evidence from many sources: 1) fossils 2) morphology (physical appearance) 3) embryological development 4) chromosomes & DNA

Dichotomous Keys Scientist group organisms based on their characteristics. These characteristics are used to make classification tools called dichotomous keys. Dichotomous keys are a series of choices that lead the user to the correct identification of on organism.

Dichotomous Key Example

Cladograms Cladistis: a method that classifies organisms according to the order that they diverged from a common ancestor. Reconstructs phylogenies based on shared characters. Cladogram: a branching diagram that represents the proposed phylogeny or evolutionary history of a species or group.

Cladogram Example

Molecular Clocks A model that is used to compare DNA sequences from two different species to estimate how long the species have been evolving since they diverged from a common ancestor.