A mutation is a genetic anomaly in a creature's genome. Mutations are divided into two main classes:

• point mutations, which only affect one factor of a gene - for example, how much glucose is needed to make a unit of glycogen
• duplications and omissions, which cause the insertion and deletion of whole sections of genetic code - for example, a chemical reaction, a brain lobe or an organ

Other mutations such as translocation are not modelled with games in the Creatures series.

Mutations are often not beneficial, although they tend to be more beneficial in the games than is usual in real life. Many things in the Creatures games (such as the critical brain lobes) are protected from mutations, as mutations in these would lead to an unacceptably high level of stillborn eggs. However, duplicates of these are typically not protected from mutation.

See the list of known mutations.