Clades and cladograms
Branching trees of ancestry.
Clade. A group of organisms that includes a common ancestor AND all of its descendants.
Cladogram. A branching tree-like diagram showing inferred evolutionary relationships:
- Root β the most recent common ancestor of everything on the tree.
- Nodes β points where lineages diverge.
- Branches β lineages connecting nodes.
- Leaves (tips) β the present-day organisms or taxa being compared.
Monophyletic group ("good" clade) β includes the common ancestor and ALL its descendants. Examples: mammals, birds.
Paraphyletic group β includes the common ancestor and SOME of its descendants. The traditional "reptiles" (excluding birds) is paraphyletic because birds evolved from reptilian ancestors and should be included to be monophyletic.
Polyphyletic group β groups organisms that do NOT share a recent common ancestor (e.g. "warm-blooded animals" lumps mammals + birds whose warmth evolved independently). Avoided in modern classification.
- Clade = ancestor + all descendants.
- Cladogram: root, nodes, branches, tips.
- Monophyletic = true clade; paraphyletic = incomplete.