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Phylogenetic Thinking

Why It Matters

When reasoning by analogy, it matters whether similarity reflects fundamental necessity or historical contingency. Features shared due to ancestry may not be required for function; features that evolved independently in response to similar pressures probably are essential. This guides what to copy and what to redesign.

The Key Move

When comparing similar things, ask: are they similar because of shared ancestry or because they solve similar problems? If ancestry, the shared features may be optional. If independent convergence, the shared features are likely essential. Build phylogenies (trees of descent) to separate these.

Classic Application

Flight. Birds, bats, and insects all have wings, but these evolved independently (analogy, not homology). The common features (airfoil shape, lightweight structure) are convergent solutions to flight physics - essential. The different implementations (feathers vs. membrane vs. chitin) are historical accidents - inessential. Convergence reveals design constraints.

Surprising Application

Organizational structures. Similar companies may have similar hierarchies because they copied each other (shared ancestry, not necessarily optimal) or because the structure solves similar coordination problems (convergence, probably essential). Phylogenetic analysis reveals which features are cargo-cult imitation versus functional necessities, guiding what to preserve during reorganization.

Failure Modes

  • Assuming all similarity is convergence: sometimes similar solutions are copied, not independently discovered. Horizontal transfer (idea copying) breaks phylogenetic assumptions.

  • Over-interpreting convergence: even independent evolution can produce different solutions to the same problem. Convergence shows constraints, not unique solutions.

  • Building incorrect phylogenies: shared features can mislead ancestry reconstruction. Molecular data often overturns morphology-based phylogenies.

Go Deeper

  • Futuyma & Kirkpatrick, Evolution (4th ed.) - Chapters on phylogenetics and homology/analogy
  • McGhee, Convergent Evolution - limits to form and predictability from convergence