Cladistics is the best method currently available for hypothesizing relationships among organisms. The basic idea behind cladistics is that members of a group share a common evolutionary history, and are “closely related,” more so to members of the same group than to other organisms.
There are three basic assumptions in cladistics:
- Any group of organisms are related by descent from a common ancestor.
- There is a bifurcating pattern of cladogenesis.
- Change in characteristics occurs in lineages over time.
In a cladogram (a cladistics tree diagram), the distance from the root of the tree can be expressed in both physical time and phylogenic distance.
It is via cladistics that we can understand that a Tyrannosaurus Rex is more closely related to modern birds than it is to a Triceratops.