Cladistics reveal the tree of life
As long as there has been life on earth new species have sprung up and old species have gone extinct. A species can be divided into two by isolation of some individuals from the rest of the species. Through this isolation a new species with characters differing from the original species might be formed. In plants new species can also be formed through hybridisation.
The diversity of species we see today has originated through repeated division of species. A tree (cladogram) over the development of species can be made to show how this development has proceeded.
All species look different and have different qualities, characters. To make a cladogram the characters able to divide the species in two or more groups are searched for. When all those grouping characters have been compiled into a table they are run in a computer program that makes cladistic trees to show how the species are related to each other. The program calculates the simplest and most plausible tree.
Sometimes a species can look very different from its nearest relatives. This can be due to adaptations to extreme environments like for example to very dry habitats of a desert. In cladistic studies the characters shared by two or more species are informative, but not characters unique to one species. The shared characters in different constellations will be the basis for a tree and show what species are the closest relatives.