Why Classify?

Why Classify? Organization is necessary when

dealing with large numbers of something

It’s easier to work if there is a system of how to keep track of things

If you have a specific place for something, then you don’t spend time hunting around trying to find it

There are some 10-30 million organisms on Earth!

Biologists organize according to similarities and proposed relationships

Tacitus bellus

A common name can be used by more than one species

A scientific name must be unique

Erithacus rubiculaRobin

Turdus migratoriusRobin

A group of organisms that can reproduce only among themselves and that are usually contained in a geographic region

Asian ElephantElephas maximus

African ElephantLoxodonta africana

Taxonomy, the ordered division of organisms into categories based on similarities and differences

Systematic Taxonomy, commonly called systematics, is the study of the evolution of biological diversity.

Populus tremuloidesQuaking Aspen

Phylogeny is the evolutionary history of a species or group of related species› classifies organisms and

their evolutionary relationships using fossils morphology embryology molecular evidence

Black Swan nestingCygnus atratus

Planet Earth is about 4.6 billion years old.

Oldest known rocks are about 3.8 billion years old.

Oldest fossils (prokaryotes) are about 3.5 billion years old.

All living organisms on this planet share a common ancestor. What is the

evidence? The tree of life reflects

the branching pattern of speciation

A phylogenetic history of life that has occurred since the origin of life.

• Swedish biologist considered the father of modern taxonomy.

• Science of Systematics dates to Linnaeus in the 18th century who devised the basic systems of binomial binomial nomenclature nomenclature and hierarchical classification hierarchical classification

• All organisms have a unique binomial name

• Humans are Homo sapiens

The arrangement of organisms in a series of nested groups, in which similar or related groups at one level are combined into larger and more general groups at the next higher level.

Biological classification is based on shared descent from the nearest common ancestor

Each categorization at any level is called a taxon.

Phylogenetic trees are constructed by studying features of organisms formally called characterscharacters.

Characters may be morphological or molecular.

Character similarity resulting from shared ancestry is called homologyhomology.

In a phylogenetic tree the tips of the branches specify particular species and the branching points represent common ancestors.

The aim is to figure out the evolutionary relationships among species.

Branching diagrams called phylogenetic trees hypothesize evolutionary relationships thought to exist among groups of organisms.

Why a hypothesis?

Cladograms are also diagrams that display patterns of shared characteristics.

Within a tree a clade is defined as a group that includes an ancestral species and all of its descendants.

Cladistics is the science of how species may be grouped into clades.

A cladogram and a phylogenetic tree are similar, but not identical.

Traditional evolutionary taxonomy is subjective and therefore more prone to bias. A phylogenetic tree’s branches put more emphasis on certain characters rather than others. . It is thought that evolutionary success is dependent on high-impact events.

Cladistics treats each character equally. It is more objective by ignoring how some characters have a higher impact on evolution

Mammals Turtles Lizards and Snakes

Crocodiles Birds Mammals Turtles Lizards and Snakes

Crocodiles Birds

CladogramPhylogeneticTree

What’s the difference? Essentially CLADISTICSCLADISTICS and PHYLOGENYPHYLOGENY are the same

Phylogenetic trees and Cladograms are usually based on a combination of these lines of evidence:

    Fossil record

    Morphology

    Embryological patterns of development

    Chromosomes and DNAChromosomes and DNA

The The fossilfossil recordrecord refers to the order in which refers to the order in which fossils appear within layers of rock that mark the fossils appear within layers of rock that mark the passing of geologic time.passing of geologic time.

Comparing physical structural characteristics

Similarities due to shared ancestry

These animals have evolved similar adaptationsadaptations because they occupy similar environments.

Convergent Evolution andConvergent Evolution andAnalogous StructuresAnalogous Structures

Convergent EvolutionConvergent EvolutionSimilar solutions to similar problems

Analogous StructuresAnalogous Structures

Analogous Structures  Traits that are morphologically and functionally similar even though there is no common ancestor.

Chromosomes and DNAChromosomes and DNA

An organism’s evolutionary history is documented in its genome

The rate of evolution of DNA sequences varies from one part of the genome to another

Comparing the different sequences helps us to investigate relationships between groups of organisms that diverged long ago

DNA that codes for ribosomal RNA and

mitochondrial DNA are both used

Amount of genetic difference between sequences is a function of time since separation.

Rate of molecular change is constant (enough) to predict times of divergence

The more alike the DNA sequences of two organisms, the more closely related they are evolutionarily.

Early phylogenetic tree of amniotes based on cytochrome c gene by Fitch and Margoliash (1967).

Note numbers on branches.

These represent estimated numbers of mutational changes in gene.

Ancestral: Trait of the

ancestor

Derived: Trait that is present in

the organism, but not in the common ancestor of the group

A dichotomous key is a written set of choices that leads to the name of an organism.

"Dichotomous" means "divided into two parts". Therefore, dichotomous keys always give two choices in each step.

After each description, the key directs the user to another pair of descriptions or identifies the organism.

Example: 1 a) Is the leaf simple? Go to 2

b) Is the leaf compound? Go to 3

2.a) Are margins of the leaf jagged? Go to 4b) Are margins of the leaf smooth? Go

to 5

A beeOsmia ribifloris on a barberry flower

When the authors of your text book were in high school they were taught two kingdoms: plants and animals.

When your teacher was in high school she was taught five kingdoms: Monera, Protista, Plantae, Fungi and Animalia

Now biologists have adopted a three-domain system › Discovery that there

are two distinct lineages of prokaryotes

Characteristic Bacteria

Archaea

Eukarya

Nuclear envelope No No Yes

Membrane-enclosed organelles

No No Yes

Introns No Yes Yes

Histone proteins associated with DNA

No Yes Yes

Circular chromosome

Yes Yes No