So far we have met two principles of phylogenetic inference:

• The parsimony principle

• The distance principle

In easy cases like that of humans, chimps, and amoebas, the distance and parsimony principles give the same result, and it might seem that it does not matter which is used.

But in other cases they differ. The parsimony principle is then more reliable, because it has a better theoretical justification. However, distance statistics are an important method in phylogenetic inference, because there are circumstances in which they are almost as reliable as parsimony - and they can often be collected more rapidly.

In order to know when any given method can be relied on, it is necessary to understand the underlying principle of phylogenetic inference.