AP Biology2/28/13

Chp.25 ~ Phylogeny & Systematics

(& Chp.26~Review the Origin of Life, Dating Fossils)

Phylogeny: the evolutionary history of

a speciesSystematics:

◦the study of biological diversity in an evolutionary context

The fossil record:◦The ordered arrangement of fossils (generally within strata of sedimentary rock)

The fossil recordSedimentary rock: rock

formed from sand and mud that once settled on the bottom of seas, lakes, and marshes

Dating:Relative~ geologic time

scale; sequence of speciesAbsolute~ radiometric

dating; age using half-lives of radioactive isotopes

Review: The Origin of Life

Early earth atmosphere◦CO2, CH4, NH4◦Very little oxygen◦Water◦Lightning

Miller-Urey Experiment (1953)

Simulated early earth conditions and added electricity (“lightning”)

Successfully created organic compounds (amino acids)

RNA World HypothesisIt is believed that RNA was present

before DNA◦RNA can replicate itself◦RNA can catalyze reactions◦Therefore, RNA could have existed as an early

form of life before DNA

After RNA was present, any organisms who developed the ability to use DNA and proteins would have been selected for, since they are superior to RNA

The First CellsThe first cells were probably

◦Prokaryotic◦Primary heterotrophs (eat their food)

OR◦Maybe simple autotrophs (make their own food)

By the time of the first cell, there would have been many organic compounds in the environment for the cells to “eat”

Biogeography: the study of the past and present distribution of species

Pangaea-250 mya Geographic isolation-180 mya

ExtinctionsExtinctions are always occurring at a low

rate (background rate)Occasionally, mass extinction events will

happen when many more species will go extinct than normally

Example:◦Permian (250 million years ago):

90% of marine animals; Pangaea merge***Human Impact on Ecosystems & Species

Extinction Rates***

Mass extinctionCretaceous (65 million years ago): death of dinosaurs, 50% of marine species; low angle comet (maybe?)

PhylogeneticsThe tracing of evolutionary relationships (phylogenetic tree)

Use Linnaean Classification

Binomial nomenclature◦Homo sapiens

Phylogenetic TreesCladistic Analysis:

taxonomic approach that classifies organisms according to the order in time at which branches arise along a phylogenetic tree (cladogram)

Clade: each evolutionary branch in a cladogram

0 = character is absent1 = character is present

Analyzing the distribution of these derived characters can provide insight into vertebrae phylogeny

PhylogeniesTypes:1. Monophyletic: single ancestor that gives rise

to all species in that taxon and to no species in any other taxon; legitimate cladogram

2. Polyphyletic: members of a taxa are derived from 2 or more ancestral forms not common to all members; does not meet cladistic criterion

3. Paraphyletic: lacks some descendants of the common ancestor; does not meet cladistic criterion

Constructing a CladogramSorting homology vs. analogy...Homology:

◦likenesses attributed to common ancestry

◦(shared ancestry)

Analogy: ◦likenesses attributed

to similar ecological roles and natural selection (convergent evolution)

Convergent EvolutionConvergent evolution:

◦species from different evolutionary branches that resemble one another due to similar ecological role Does not show an evolutionary relationship

When species develop similar adaptations because of similar environments◦Dolphins and sharks◦Flying insects and birds

Analogy – Convergent EvolutionThese structures

are analogous, because they did not come from a common ancestor but were evolved separately

Patterns of Evolution

Coevolution◦Species evolve together because of some relationship Predator/Prey or Parasite/Host:

◦“Evolutionary arms race” Symbiotic relationships

◦Flowers (Plants ) and pollinators (insects, bats, birds)

Human EvolutionHumans and chimpanzees last had a

common ancestor about 6 million years agoThe genus Homo evolved approximately 2

million years ago and included several species (although only Homo sapiens is still alive)

Anatomically modern human is approximately 200,000 years old

Human Traits (not exclusive to Homo sapiens)

Bipedalism (walk upright)◦“Lucy” – nearly complete skeleton of

Australopithecus afarensis – 3 million years agoLarge brain, good reasoning skills, tool-

making (not exclusively human)Extended childhoodSpeech (hyoid bone)

According to this phylogeny, humans are most closely related to chimpanzees (Genus Pan). (split ~ 6 mya)The ancestor of gorillas branched off earlier in evolution (~8 mya).Pongo = OrangutanHylobates = gibbons

Homo ergasterAncestor or

subspecies of H. erectus

Lake Turkana, Kenya (“Turkana Boy”) discovered by Richard Leakey

Used tools

Phylogenetic Trees/Cladograms Practice

Mass Extinctions