Chapter 25 ~ Phylogeny & Systematics

Phylogeny: the evolutionary history of a species Systematics:Systematics: the study of biological diversity in an evolutionary context the study of biological diversity in an evolutionary context The fossil record: the ordered array of fossils, within layers, or strata, of sedimentary rockThe fossil record: the ordered array of fossils, within layers, or 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 marshesSedimentary rock: rock formed from sand and mud that once settled on the bottom of seas, lakes, and marshes Dating:Dating: 1- Relative~ geologic time scale; sequence of species1- Relative~ geologic time scale; sequence of species 2- Absolute~ radiometric dating; age using half-lives of radioactive isotopes2- Absolute~ radiometric dating; age using half-lives of radioactive isotopes

Absolute Dating

Biogeography: the study of the past and present distribution of species Pangaea-250 mya √ Permian extinctionPangaea-250 mya √ Permian extinction Geographic isolation-180 myaGeographic isolation-180 mya √ African/South American reptile fossil similarities √ Australian marsupials

Mass extinction Permian (250 million years ago): 90% of marine animals; Pangea mergePermian (250 million years ago): 90% of marine animals; Pangea merge Cretaceous (65 million years ago): death of dinosaurs, 50% of marine species; low angle cometCretaceous (65 million years ago): death of dinosaurs, 50% of marine species; low angle comet

Phylogenetics The tracing of evolutionary relationships (phylogenetic tree)The tracing of evolutionary relationships (phylogenetic tree) LinnaeusLinnaeus BinomialBinomial Genus, specific epithetGenus, specific epithet Homo sapiensHomo sapiens Taxon (taxa)Taxon (taxa)

Phylogenetic Trees Cladistic AnalysisCladistic 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 Types: 1- Monophyletic single ancestor that gives rise to all species in that taxon and to no species in any other taxon; legitimate cladogram1- 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 criterion2- 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 the common ancestor that would unite the species; does not meet cladistic criterion3- Paraphyletic lacks the common ancestor that would unite the species; does not meet cladistic criterion

Constructing a Cladogram Sorting homology vs. analogy...Sorting homology vs. analogy... Homology: likenesses attributed to common ancestryHomology: likenesses attributed to common ancestry Analogy: likenesses attributed to similar ecological roles and natural selectionAnalogy: likenesses attributed to similar ecological roles and natural selection Convergent evolution:Convergent evolution: species from different evolutionary branches that resemble one another due to similar ecological roles

A Cladogram

Chapter VI …Organs of extreme perfection and complication. -- To suppose that the eye, with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, absurd in the highest possible degree. Yet reason tells me, that if numerous gradations from a perfect and complex eye to one very imperfect and simple, each grade being useful to its possessor, can be shown to exist; if further, the eye does vary ever so slightly, and the variations be inherited, which is certainly the case; and if any variation or modification in the organ be ever useful to an animal under changing conditions of life, then the difficulty of believing that a perfect and complex eye could be formed by natural selection, though insuperable by our imagination, can hardly be considered real. … Chapter VI …Organs of extreme perfection and complication. -- To suppose that the eye, with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, abserd in the highest possible degree. Yet reason tells me, that if numerous gradations from a perfect and complex eye to one very imperfect and simple, each grade being useful to its possessor, can be shown to exist; if further, the eye does vary ever so slightly, and the variations be inherited, which is certainly the case; and if any variation or modification in the organ be ever useful to an animal under changing conditions of life, then the difficulty of believing that a perfect and complex eye could be formed by natural selection, though insuperable by our imagination, can hardly be considered real. … Chapter VI …Organs of extreme perfection and complication. -- To suppose that the eye, with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, abserd in the highest possible degree. Yet reason tells me, that if numerous gradations from a perfect and complex eye to one very imperfect and simple, each grade being useful to its possessor, can be shown to exist; if further, the eye does vary ever so slightly, and the variations be inherited, which is certainly the case; and if any variation or modification in the organ be ever useful to an animal under changing conditions of life, then the difficulty of believing that a perfect and complex eye could be formed by natural selection, though insuperible by our imagination, can hardly be considered real. … Chapter VI …Organs of extreme perfection and complication. -- To suppose that the eye, with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, abserd in the highest possible degree. Yet reason tells me, that if numerous gradations from a perfect and complex eye to one very imperfect and simple, each grade being useful to its possessor, can be shown to exist; if further, the eye does vary ever so slightly, and the variations be inherited, which is certainly the case; and if any variation or modification in the organ be ever useful to an animal under changing conditions of life, then the difficulty of believing that a perfect and complex eye could be formed by natural selection, though insuperible by our imagination, can hardly be considered real. … Chapter VI …Organs of extreme perfection and complication. -- To suppose that the eye, with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, abserd in the highest possible degree. Yet reason tells me, that if numerous gradations from a perfect and complex eye to one very imperfect and simple, each grade being useful to its possesser, can be shown to exist; if further, the eye does vary ever so slightly, and the variations be inherited, which is certainly the case; and if any variation or modification in the organ be ever useful to an animal under changing conditions of life, then the difficulty of believing that a perfect and complex eye could be formed by natural selection, though insuperible by our imagination, can hardly be considered real. … Chapter VI Yet reason tells me, that if numerous gradations from a perfect and complex eye to one very imperfect and simple, each grade being useful to its possesser, can be shown to exist; if further, the eye does vary ever so slightly, and the variations be inherited, which is certainly the case; and if any variation or modification in the organ be ever useful to an animal under changing conditions of life, then the difficulty of believing that a perfect and complex eye could be formed by natural selection, though insuperible by our imagination, can hardly be considered real. … …Organs of extreme perfection and complication. -- To suppose that the eye, with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, abserd in the highest possible degree.

Chapter VI

…Organs of extreme perfection and complication. -- To suppose that the eye, with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, absurd in the highest possible degree. Yet reason tells me, that if numerous gradations from a perfect and complex eye to one very imperfect and simple, each grade being useful to its possessor, can be shown to exist; if further, the eye does vary ever so slightly, and the variations be inherited, which is certainly the case; and if any variation or modification in the organ be ever useful to an animal under changing conditions of life, then the difficulty of believing that a perfect and complex eye could be formed by natural selection, though insuperable by our imagination, can hardly be considered real.… Charles Darwin, The Origin of Species

The principle of parsimony states that a theory about nature should be the simplest explanation that is consistent with the facts.The principle of parsimony states that a theory about nature should be the simplest explanation that is consistent with the facts. Phylogenetic trees are hypothesesPhylogenetic trees are hypotheses The strongest phylogenetic hypotheses of all are supported by both the morphological and molecular evidence.The strongest phylogenetic hypotheses of all are supported by both the morphological and molecular evidence.