Phylogenetic Trees

Graph Theory · Axiom Academy

How graph theory helps us understand evolution, track diseases, and map the tree of life Every species on Earth is connected through a vast family tree spanning billions of years. But how do scientists map these relationships? The answer lies in phylogenetic trees —mathematical structures that use the principles of graph theory to represent evolutionary history. When COVID-19 emerged, scientists used phylogenetic trees to track how the virus evolved and spread across the globe. From vaccine development to outbreak prediction, these trees became essential tools in the pandemic response. Key Insight: A phylogenetic tree is just a special type of graph where leaves represent living species and internal nodes represent hypothetical common ancestors. The structure reveals evolutionary relationships! Anatomy of an Evolutionary Tree Let's break down the mathematical structure. A phylogenetic tree is a rooted, acyclic, directed graph with special properties: Leaves (Terminal Nodes): Living species or DNA sequences we can observe today Internal Nodes: Hypothetical common ancestors (extinct species) Branches (Edges): Evolutionary pathways showing descent with modification Root: The most recent common ancestor of all species in the tree Here's a real example—let's explore the evolutionary tree of great apes: How do scientists actually construct these trees? The answer lies in comparing DNA sequences. Every mutation in DNA is like a branch point in our evolutionary tree!

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