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Why does the position of two species next to each other on a phylogenetic tree not always show close relatedness?

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A diagram showing the tentative evolutionary relationships among hominid species over the past four million years, with skull images and labeled species names connected by solid and dotted lines to indicate proposed evolutionary pathways. — phylogeny Tentative phylogenetic scheme for the evolution of the human lineage. Solid bars indicate the time ranges during which species are thought to have existed, based on fossil evidence. Dotted lines signify evolutionary relationships between hominin species that have been proposed on the basis of the fossil evidence.

The position of two species next to each other on a phylogenetic tree does not always indicate close relatedness because these diagrams depict lines of descent rather than physical similarity or proximity.1

In phylogenetics, relatedness is defined strictly by the recency of a common ancestor, represented by a node where branches intersect. Because the branches of a tree can be rotated at any node without altering the underlying evolutionary information, two species may appear adjacent simply due to the specific layout chosen by the illustrator.12

To accurately determine how closely related two organisms are, you must trace their respective branches back to the most recent common ancestor they share. Proximity at the tips of the tree is often a visual artifact of the diagram's orientation and does not necessarily reflect the true evolutionary distance between the organisms.12