Download - Available at Evolution: Patterns of Similarity and Divergence Vanessa Couldridge Richard Knight
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Evolution: Patterns of Similarity and Divergence
Vanessa Couldridge
Richard Knight
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Species are grouped according to their similarity or evolutionary history
First performed by Linnaeus on the basis of physical characteristics
Molecular techniques more widely used today
Classification of OrganismsClassification of Organisms
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Assignment of a unique two part scientific name to each species of organism
Example: Homo sapiens
Scientific name is written in italics and the genus name begins with a Capital Letter
Can be abbreviated, e.g. H. sapiens and H. habilis
Homo sp. means a single species in the genus Homo
Homo spp. means more than one species in the genus Homo
Binomial NomenclatureBinomial Nomenclature
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GenusGenus SpeciesSpecies
Corresponding structures in different species are the result of a shared common ancestor
HomologyHomology
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Anatomical features in different species resemble each other, but did not arise from a common ancestry
Example: Spider leg and mammal leg
HomoplasyHomoplasy
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Non-homologous features share the same function, but not necessarily the same structure
Example: Fish gills and human lungs
AnalogyAnalogy
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Convergent evolution
Unrelated species become similar
Parallel evolution
Related species continue to evolve similar characteristics
Divergent evolution
Related species become dissimilar
Patterns of EvolutionPatterns of Evolution
Unrelated organisms evolve similar features and come to resemble one another
Example: Marsupials and placental mammals
Convergent EvolutionConvergent Evolution
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Thylacine (marsupial)Thylacine (marsupial) Golden jackal (mammal)Golden jackal (mammal)
Two or more species from a similar evolutionary history continue to evolve similar characteristics
Example: Social behaviour in bees, wasps and ants
Parallel EvolutionParallel Evolution
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Two or more species that share a common ancestor become progressively dissimilar due to differing environmental pressures
Example: Red fox and kit fox
Divergent EvolutionDivergent Evolution
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Method of classifying organisms according to common ancestry, based on their dichotomous branching in an evolutionary tree
Uses shared derived characteristics
Tree of relationships is called a cladogram
Subset of related organisms is called a clade
CladisticsCladistics
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CLADOGRAMCLADOGRAM
Cladogram of five vertebrates: lizard, cow, seal, dog, cat
The presence of hair can be used as the first branching point to separate the lizard from the others
Cladistics: ExampleCladistics: Example
The presence of involuted cheek teeth in the cat, dog and seal, but not the cow, determines the next branching point
The cat and dog can be separated from the seal based on the presence of carnassial teeth
Retra
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Invo
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Hair
Hair
CATCAT DOGDOG LIZARDLIZARDCOWCOWSEALSEAL
Finally, retractable claws in cats separates them from dogs
Method of classification that takes into account:
Splitting of branches in the phylogenetic tree
Major evolutionary changes
Systematics differs to cladistics in that it weighs derived characters according to their degree of evolutionary significance, whereas cladistics treats all derived characters equally
SystematicsSystematics
LUNGFISHLUNGFISHCOWCOW TROUTTROUT
CLADISTICCLADISTICCLASSIFICATIONCLASSIFICATION
Consider the relationship between the cow, lungfish and trout as an example
In the cladistic approach, cows and lungfish are more closely related to each other than either is to the trout, because they share a novel feature (internal nares)
In the systematic approach, the lungfish and the trout are more closely related to each other than either is to the cow, because the cow is a mammal and the other two are both fishes
SystematicsSystematics
LUNGFISHLUNGFISHCOWCOW TROUTTROUT
EVOLUTIONARYEVOLUTIONARYCLASSIFICATIONCLASSIFICATION
Organisms classified according to a series of ranks that become progressively less inclusive
Originally proposed by Linnaeus, who identified
Three kingdoms:
Animal, vegetable, mineral
Five ranks:
Class, order, genus, species, variety
Systematic HierarchySystematic Hierarchy
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Eight major ranks:
Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species
Classification may be further divided, for example, superorder (above order) and suborder (below order)
Systematic HierarchySystematic Hierarchy
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FRUIT FLYFRUIT FLY
DomainDomain EukaryotaEukaryotaKingdomKingdom AnimaliaAnimaliaPhylumPhylum ArthropodaArthropodaSubphylumSubphylum HexapodaHexapodaClassClass InsectaInsectaSubclassSubclass PterygotaPterygotaOrderOrder DipteraDipteraSuborderSuborder BrachyceraBrachyceraFamilyFamily DrosophilidaeDrosophilidaeSubfamilySubfamily DrosophilinaeDrosophilinaeGenusGenus DrosophilaDrosophilaSpeciesSpecies melanogastermelanogaster