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•  Natural classifications help in identification of species and allow the prediction of characteristics shared by 

    species within a group

Historically, there have been two main classification schemes used to identify living organisms – artificial and natural classification

  • Both use prominent features as the basis for classification, however differ in the way these characteristics are established

Artificial classification involves arbitrarily selecting unifying characteristics first and then grouping organisms accordingly

  • The advantage of artificial classification is that such schemes are easy to develop and relatively stable (unlikely to change)
  • The disadvantage is that they do not generally show evolutionary relationships and for this reason are not commonly used
    • For example, if organisms were classified according to the presence of fins then whales would be grouped with fish
    • If organisms were classified based on the presence of shells then snails would be grouped with turtles and not with squid

Natural classification involves grouping organisms based on similarities first and then identifying shared characteristics

  • According to a natural classification system, all members of a particular group would have shared a common ancestor
  • This means that natural classification schemes can be used to predict characteristics shared by species within a group
  • A disadvantage of such schemes is that they are highly mutable and tend to change as new information is discovered

A third type of classification – phylogenetic classification – is now being used to differentiate organisms based on genetics

  • Organisms who share a greater level of homology in their DNA or amino acid sequences are expected to be more closely related

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•  In a natural classification, the genus and accompanying higher taxa consist of all the species that have evolved 

    from one common ancestral species

An advantage of natural classification is that it identifies traits based on groupings, rather than assigning groups based on traits

  • This means that it can be used to show evolutionary relationships and predict characteristics shared by species within a group

According to natural classification, each taxonomic level includes all species that would have evolved from a common ancestor

  • Species of the same genus would have a common genus ancestor and be more closely related than species of the same order
  • Hence, organisms that share a lower taxa must share all higher taxa (e.g. if the same order then must also be the same class)

Identifying Evolutionary Relationships Using Natural Classification

natural classification

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•  Taxonomists sometimes reclassify groups of species when new evidence shows that a previous taxon contains

    species that have evolved from different ancestral species

A disadvantage of natural classifications is that because they predict evolutionary relationships, they change with new information

  • Taxonomists will reclassify groups of species when new evidence arises to compromise the traditional classification scheme

Groups of species may be separated into different genera if new evidence suggests they evolved from different ancestral species

  • Species originally classified as figworts have been reclassified into different genera based on DNA sequence comparisons

Alternatively, different species may be grouped into a shared taxon if new evidence suggests more recent common ancestry 

  • The Homininae sub-family was created to include gorillas and chimpanzees when it was deduced that they share more common ancestry with humans than with other great apes (e.g. orang-utan)

Reclassification of Hominids

hominid classification