From Creatures Wikia
Multi-lobed creatures are those with an abnormally high brain lobe count for their species and/or game. Multi-lobedness occurs when a new brain lobe gene is formed, though many are simple duplications and so they occupy the same space in the brain and don't make the creature any smarter. In Creatures 1, where the normal brain lobe count is 9, creatures have been reported to have lobe counts of 36 or more. This mutation can occur in Creatures 1 or 2, but Creatures 3 norns' brains do not mutate.