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
Natural classification is very useful for research into biodiversity. It is easier in identification of new species that do not obviously fit into a specific classification (Kingdom --> Phylum --> Class à etc.)
- Artificial classification involves arbitrarily selecting unifying characteristics first and then grouping organisms accordingly
- Natural classification involves grouping organisms based on similarities first and then identifying shared characteristics.
- A third type of classification – phylogenetic classification – is now being used to differentiate organisms based on genetics
Natural classification is very useful for research into biodiversity. It is easier in identification of new species that do not obviously fit into a specific classification (Kingdom --> Phylum --> Class à etc.)
- A dichotomous key could be used to put an organism into a classification that fits that organism the best
- This would not work as well for artificial classification (eg. Colour of flower petals)
- Since organism evolved from a common ancestor, new species would share similar characteristics (likely internal), allowing for easier identification and classification. For example the pentadactyl limb, or mammary glands in mammals
Understanding:
5.3.U6: In a natural classification, the genus and accompanying higher taxa consist of all the species that have evolved from one common ancestral species.
Objectives:
5.3.U6: In a natural classification, the genus and accompanying higher taxa consist of all the species that have evolved from one common ancestral species.
Objectives:
- Define natural classification.
- List two difficulties in determining the natural classification of species.
An advantage of natural classification is that it identifies traits based on groupings, rather than assigning groups based on traits
According to natural classification, each taxonomic level includes all species that would have evolved from a common ancestor
- 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
Understanding:
5.3.U7: Taxonomists sometimes reclassify groups of species when new evidence shows that a previous taxon contains species that have evolved from different ancestral species.
Objectives:
5.3.U7: Taxonomists sometimes reclassify groups of species when new evidence shows that a previous taxon contains species that have evolved from different ancestral species.
Objectives:
- List two situations in which the reclassification of a species may be necessary.
- Outline an example of a species (or group of species) which were reclassified when new evidence was discovered.
A disadvantage of natural classifications is that because they predict evolutionary relationships, they change with new information
Groups of species may be separated into different genera if new evidence suggests they evolved from different ancestral species
Alternatively, different species may be grouped into a shared taxon if new evidence suggests more recent common ancestry
- 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