Creatures Wiki

The details of creatures in games in the Creatures series - such as their brains, biochemistry and appearance - are to a great degree dictated by virtual genetics using a simulated genome; often called Digital DNA.

Things which are defined in genomes include:

Each individual 'gene' of a genome can mutate in various ways and lead to interesting new behaviours which the original designers never thought of.

There are editors available which let you manipulate the genetics directly and birth new creatures with them, such as the Genetics Kit.