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AP Biology 2/28/13. Chp.25 ~ Phylogeny & Systematics (& Chp.26~Review the Origin of Life, Dating Fossils). Phylogeny: the evolutionary history of a species. Systematics : the study of biological diversity in an evolutionary context The fossil record :
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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 species • Systematics: • 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 record • Sedimentary 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 species • Absolute~ 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)
It 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 RNA World Hypothesis
The 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” The First Cells
Biogeography: the study of the past and present distribution of species • Pangaea-250 mya • Geographic isolation-180 mya
Extinctions 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*** Extinctions
Mass extinction • Cretaceous(65 million years ago): death of dinosaurs, 50% of marine species; low angle comet (maybe?)
Phylogenetics • The tracing of evolutionary relationships (phylogenetic tree) • Use Linnaean Classification • Binomial nomenclature • Homo sapiens
Phylogenetic Trees • CladisticAnalysis: 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
Analyzing the distribution of these derived characters can provide insight into vertebrae phylogeny 0 = character is absent 1 = character is present
Phylogenies • Types: • Monophyletic: single ancestor that gives rise to all species in that taxon and to no species in any other taxon; legitimate cladogram • Polyphyletic: members of a taxa are derived from 2 or more ancestral forms not common to all members; does not meet cladistic criterion • Paraphyletic: lacks some descendants of the common ancestor; does not meet cladistic criterion
Sorting homology vs. analogy... • Homology: • likenesses attributed to common ancestry • (shared ancestry) • Analogy: • likenesses attributed to similar ecological roles and natural selection (convergent evolution) Constructing a Cladogram
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 Convergent Evolution
Analogy – Convergent Evolution • These structures are analogous, because they did not come from a common ancestor but were evolved separately
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) Patterns of 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 Evolution
Bipedalism (walk upright) • “Lucy” – nearly complete skeleton of Australopithecus afarensis – 3 million years ago • Large brain, good reasoning skills, tool-making (not exclusively human) • Extended childhood • Speech (hyoid bone) Human Traits (not exclusive to Homo sapiens)
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 = Orangutan Hylobates = gibbons
Ancestor or subspecies of H. erectus • Lake Turkana, Kenya (“Turkana Boy”) discovered by Richard Leakey • Used tools Homo ergaster