Distance measures are used in phylogeny and refer to the quantitatively measured difference between two groups of organisms, such as two species.

Distance can be measured in two ways:

• The difference between the phenetic appearance of two groups (phenetic distance).

• The difference in their gene frequencies (genetic distance).

Distance is simply a more precise method of the 'look more similar' approach which classifies humans and chimpanzees (pictured opposite) as having a more recent common ancestor than humans and rabbits because they share more phenetic characters.