Definition
Phylogeny is the branching pattern of evolutionary descent among organisms — the genealogical tree that connects every species to every other through common ancestors. A phylogenetic tree has tips (extant or extinct taxa), internal nodes (last common ancestors), and branches whose lengths can represent time, accumulated change, or both.
In paleoanthropology, the phylogeny of interest is the hominin tree: which fossil species are ancestors and which are side-branches, where each lineage split, and how those splits relate to the splits among other apes. The tree is reconstructed from shared derived characters (synapomorphies) and, where data permit, from molecular comparisons.
Why it matters
How it works
To build a phylogeny, the analyst codes a matrix of characters — each species scored for each trait (e.g. canine size, foramen magnum position, cranial capacity). Cladistic algorithms then search for the tree that explains the observed character distribution with the fewest evolutionary changes (parsimony) or the highest likelihood under a model of evolution.
Molecular phylogenies use DNA or protein sequences instead of anatomical characters and benefit from huge numbers of independent sites. They have rewritten parts of the great-ape tree — confirming that chimps, not gorillas, are our closest living relatives — but most hominin fossils are too old for DNA, so morphology still does the heavy lifting before about 400,000 years ago.