Chapter 25 ~ Chapter 25 ~

Phylogeny & SystematicsPhylogeny & Systematics

Phylogeny:Phylogeny: the evolutionary history of a speciesthe evolutionary history of a species

• SystematicsSystematics:: the study of biological the study of biological

diversity in an diversity in an evolutionary contextevolutionary context

• The fossil recordThe fossil record: : the ordered array of the ordered array of fossils, within layers, fossils, within layers, or strata, of or strata, of sedimentary rocksedimentary rock

The fossil recordThe fossil record• Sedimentary rockSedimentary rock: rock : rock

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

•DatingDating::•1-1- Relative~ Relative~ geologic time geologic time scale; sequence of speciesscale; sequence of species•2-2- Absolute~ Absolute~ radiometric radiometric dating; age using half-lives of dating; age using half-lives of radioactive isotopesradioactive isotopes

Absolute DatingAbsolute Dating

BiogeographyBiogeography: : the the study of the past and study of the past and

present distribution of present distribution of speciesspecies

• PangaeaPangaea-250 mya -250 mya √ Permian extinction√ Permian extinction

• Geographic isolationGeographic isolation-180 mya-180 mya

√ √ African/South African/South American reptile American reptile

fossil fossil similarities similarities

√ √ Australian marsupialsAustralian marsupials

Mass extinctionMass extinction• PermianPermian

(250 million years (250 million years ago): 90% of ago): 90% of marine animals; marine animals; Pangea mergePangea merge

• CretaceousCretaceous (65 million years (65 million years ago): death of ago): death of dinosaurs, 50% of dinosaurs, 50% of marine species; low marine species; low angle cometangle comet

PhylogeneticsPhylogenetics• The tracing of The tracing of

evolutionary evolutionary relationships relationships ((phylogenetic treephylogenetic tree))

• LinnaeusLinnaeus

• BinomialBinomial

• Genus, specific epithetGenus, specific epithet

• Homo sapiensHomo sapiens

• Taxon (taxa)Taxon (taxa)

Phylogenetic TreesPhylogenetic 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- 1- MonophyleticMonophyletic single ancestor that gives rise to all single ancestor that gives rise to all species in that taxon and to no species in any other taxon; species in that taxon and to no species in any other taxon; legitimate cladogramlegitimate cladogram

• 2- 2- PolyphyleticPolyphyletic members of a taxa are derived from 2 or members of a taxa are derived from 2 or more ancestral forms not common to all members; does more ancestral forms not common to all members; does not meet cladistic criterionnot meet cladistic criterion

• 3- 3- Paraphyletic Paraphyletic lacks the common ancestor that would lacks the common ancestor that would unite the species; does not meet cladistic criterionunite the species; does not meet cladistic criterion

Constructing a CladogramConstructing a Cladogram• Sorting homology vs. analogy...Sorting homology vs. analogy...

• HomologyHomology: : likenesses attributed to likenesses attributed to common ancestrycommon ancestry

• AnalogyAnalogy: : likenesses attributed to likenesses attributed to similar ecological roles and similar ecological roles and natural selectionnatural selection

• Convergent evolutionConvergent evolution: :

species from different species from different evolutionary branches evolutionary branches

that that resemble one another due resemble one another due to to similar ecological rolessimilar ecological roles

A CladogramA 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

Chapter VI

Chapter VI

Chapter VI

Chapter VI

Chapter VI

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 The principle of parsimony states that a theory about nature should be that a theory about nature should be the simplest explanation that is the simplest explanation that is consistent with the facts.consistent with the facts.

• Phylogenetic trees are hypothesesPhylogenetic trees are hypotheses• The strongest phylogenetic The strongest phylogenetic

hypotheses of all are supported by hypotheses of all are supported by both the morphological and both the morphological and molecular evidence.molecular evidence.