ClassificationClassification

Finding Order in Diversity

Biologists have…

• identified and named 1.5 million different species

• estimate 2-100 million additional species have yet to be discovered

Why Classify?Why Classify?

• To study the diversity of life, scientists must name each organism

• Scientists use a classification system to name organisms and group them in a logical manner

• Taxonomy is the study of naming organisms– Names are universally accepted– Names have biological significance– Categories go from larger groups to smaller

groups.• Ex) teacher= larger, biology teacher = smaller

Assigning Scientific Names

• Calling things by their common name can be confusing– Names change by region

• Ex) puma, mountain lion, panther & cougar are all regional names for Felis concolor

• In the 18th century scientists used Latin & Greek to assign scientific names, because these languages were common to all.

Early Naming

• In the beginning, scientific names were often detailed physical descriptions– Often names were 20+ words long

• There was difficulty in standardizing names because different scientists described organisms differently– Ex) the blue-winged/red breasted/ white stomached bird

Binomial Nomenclature• Carolus Linnaeus developed a

two word naming system called binomial nomenclature

• Each species is give a two part scientific name:– The name is written in italics– The first word is capitalized and

the second is written in lowercase

– The first word is the genus (closely related species) – The second word is the species (name usually describes an

important trait)

Linnaeus’s System of Classification

• Hierarchal system, with seven levels

• Each level is referred to as a taxon

• From largest to smallest:– Kingdom– Phylum– Class– Order– Family – Genus – Species

“King Philip Cried Out For Good Soup”

Which similarities are most important?

• Organisms that look very similar may not share a common ancestor.

• Their similar appearance may be the result of convergent evolution.

• Darwin’s idea of descent with modification gave rise to the study of phylogeny, or evolutionary relationships among organisms.

Evolutionary Classification• Biologists now group

organisms into categories that represent lines of descent, or phylogeny, not just physical similarities.

• Species within a genus are more closely related to each other than to those in another genus because they share a recent common ancestor.

• The higher the level of the first taxon in common between two organisms, the farther back in time the common ancestor.

Classification Using Cladograms

• Cladistic analysis: identification and consideration of only those characteristics of organisms that are evolutionary innovations (new characteristics that arise as lineages evolve over time)– Characteristics that appear in recent parts of lineage but not

older members are called derived characteristics– These characteristics can be used to construct a cladogram to

show the evolutionary relationships between organisms– Cladograms are useful tools for scientists to understand how

one lineage branched from another in the course of evolution.

Similarities in DNA & RNA

• The genes of many organisms show important similarities at the molecular level.

• Similarities in DNA can be used to help determine classification and evolutionary relationships

• The more similar the DNA sequence of two species, the more recently they shared a common ancestor and the more closely related they are in evolutionary terms.

Molecular Clocks• Comparisons of DNA can

also be used to mark the passage of evolutionary time.

• A molecular clock uses DNA comparisons to estimate the length of time that two species have been evolving independently.

• A molecular clock relies on mutations to mark time.

• The degree of dissimilarity in the DNA of two species indicates how long ago the two species shared a common ancestor.