Download Biodiversity 1.5 million species have been identified on Earth and it

Biodiversity
1.5 million species have been identified on Earth and it is believed that there are millions more to
be discovered. Biologists use a classification system to name organisms and group them in a
logical way. This naming and classification is known as taxonomy.
Binomial nomenclature assigns a two part name to each organism. These names are written in
italics with the first name capitalized and the second name in lower case. The first part of the
name is the genus and the second part is the species.
There are eight taxa, or levels, in the classification system used for organisms. From largest to
smallest, they are: domain, kingdom, phylum, class, order, family, genus, species.
Evolutionary Classification
Evolutionary classification is the grouping of organisms into categories that represent lines of
evolutionary descent or phylogeny. Organisms in the same species are more closely related than
organisms that share higher levels of taxa.
Cladograms are used to show the evolutionary relationships among organisms. They help how
one linage of organisms branched from another during evolution. Characteristics that appear in
recent parts of a lineage are called derived characteristics.
Similar DNA and RNA
The genes in many organisms show similarities. Similar DNA can be used to help determine
classification and evolutionary relationships. It is assumed that the more similar the DNA from
two organism is, the more recently they have shared a common ancestor. A model called a
molecular clock uses DNA comparisons to estimate how long two species have been evolving
independently. The less similarity between the DNA, the longer they have been evolving
independently.