Read relationships from a tree

Explanation

Biological classification organises species by shared characteristics, increasingly interpreted in the light of evolutionary relationships. A phylogeny represents hypotheses about those relationships and common ancestry. Groups should be based on meaningful shared evidence rather than superficial similarity alone.

In a rooted tree, internal nodes represent inferred common ancestors and branches represent lineages. Two taxa sharing a more recent common ancestor are more closely related than either is to a taxon joining at an older node. Living taxa at the tips need not be ancestors of one another.

Rotating branches around a node changes the drawing order without changing the relationships. Branch length has meaning only if the tree provides a scale, such as time or genetic change. A long line on an unscaled cladogram is not proof of a greater amount of evolution.

Shared derived characters help identify nested groups. A classification can be revised when molecular or anatomical evidence changes the supported relationships. The tree is a testable model based on data, not an image that proves its own accuracy.