How are organisms grouped together?

Organisms grouped together according to similarities listed above.
Natural classification:
- Based on homologous structures.
- These have shared evolutionary origin.
- They have similar structure and position, regardless of function.
- Eg pentadactyl limb – arrangement of 5 digits in limbs of terrestrial vertebrates.
Should not be based on analogous structures.
These have similar function but do not have a common origin.
- Eg. wings in birds and bats.
This is an artificial classification.

Taxonomy

Taxon = a group within a natural classification
When it comes to IBDP Biology, Taxonomy = the study of these groups.
This involves:
- Arranging all organisms into a system of hierarchical groups
- Deciding what groups newly discovered species should occupy.
  - These species may be alive today or extinct fossils.

A series of rank names.
Allows larger groups to be differentiated from larger groups.
When it comes to IBDP Biology, It is hierarchical – large groups are subdivided into smaller groups.
There is no overlap between each group.
The smaller the group that two organisms can be placed into, the closer they are related through evolution.
Eg humans and jelly fish are animals.
Humans and fish are vertebrates (chordata).
Humans and mice are mammals.
Humans and monkeys are primates.
However, It does not demonstrate how closely related 2 groups are within a larger group.

A phylogenetic classification system shows the evolutionary lnks between each taxonomic group with respect to time.
When it comes to IBDP Biology, It can be represented a s a phylogentic tree.

Eg Reptiles, birds and mammals are all chordates.
- Reptiles and birds have a common ancestor.
- Mammals diverged from reptiles before birds evolved.
- This is not indicated by the taxonomic ranks.

That's the end of this topic.