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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 Evolution
Convergent 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 Evolution
These 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 Evolution
Humans and chimpanzees last had a common ancestor about 6 million years ago
The 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