Evidence for Evolution

Comparative genomics compares the molecules of different species to work out how closely related they are. The rule of thumb: more closely related species have fewer differences in their DNA and proteins.

Techniques

• Protein sequencing — comparing shared proteins like cytochrome c.
• DNA–DNA hybridisation — measuring how well DNA from two species binds together (more binding = more similar).
• DNA & rRNA sequencing — comparing base sequences directly.

Because mutations build up at a roughly steady rate, the number of differences acts as a molecular clock — more differences means longer since two species shared an ancestor.

Phylogenetic trees

The results are drawn as a phylogenetic tree: each branch point is a common ancestor, and the closer two species branch, the more recently they diverged.

A phylogenetic tree: A and B branch more recently, so they're more closely related than C.