Summary
A classification method grouping organisms by shared derived characteristics into clades.
In depth
Clades are groups sharing a common ancestor and all its descendants. Characters are polarised using an outgroup; shared derived characters (synapomorphies) define clades and shared ancestral traits do not. Parsimony prefers the tree needing the fewest changes.
Birds are a clade within dinosaurs.
A monophyletic group (clade) includes an ancestor and all descendants; paraphyletic groups leave some out (reptiles without birds), and polyphyletic groups combine unrelated lineages (warm-blooded animals as birds plus mammals). Cladistic classification aims to name only monophyletic groups, so birds are within Dinosauria and Reptilia.
Methods include parsimony (the tree needing fewest changes), and today often likelihood or Bayesian methods. Cladograms show branching order but not time. Homoplasy, such as convergence, produces misleading characters, so a good dataset has many. Willi Hennig founded the method in the 1950s.
Example: feathers are a synapomorphy of a clade including birds and many theropod dinosaurs.
Frequently asked questions
What is Cladistics?
A classification method grouping organisms by shared derived characteristics into clades.
Which area of biology covers Cladistics, and how advanced is it?
Cladistics is one of the 53 topics in Evolution. It is rated Intermediate, so it suits learners who already know the core vocabulary. Related topics in this area include Phylogenetic Trees, Macroevolution, Founder Effect and Bottleneck.
Can you give an example of Cladistics?
'reptiles' excluding birds is paraphyletic.
What should I learn before Cladistics?
Work through the Beginner topics in Evolution first, such as Evolution, Natural Selection, Charles Darwin, then return to Cladistics. Intermediate topics assume the Beginner vocabulary.
What topics are related to Cladistics?
The closest topics to Cladistics are Phylogenetic Trees, Macroevolution, Founder Effect and Bottleneck, Maximum Likelihood Phylogenetics. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Cladistics?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Cladistics. To practise the whole of Evolution, use the Evolution quiz.
How is Cladistics different from Phylogenetic Trees?
Cladistics: A classification method grouping organisms by shared derived characteristics into clades. Phylogenetic Trees: Branching diagrams that show inferred evolutionary relationships among species. Read both side by side and note what each one explains.
How should I study Cladistics step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Phylogenetic Trees and explain the difference aloud. Finally, take the Evolution quiz and come back to this page for any question you miss.