Gerard has brain damage that has affected his long term memory and ability to navigate in his environment. gerard most likely has damage to his:

Gerard MOST likely has damage to his: hippocampus.

The hippocampus is a small, seahorse shaped structure situated in the temporal lobe part of the brain. The primary function of the hippocampus involves memory and human learning. The hippocampus helps in the formation of new memories and is also associated with emotions. Two hippocampi are present in humans which helps to process and retrieve two types of memory, which are; declarative memories (which involves facts and events), and spatial relationships (which involves routes). Damage to any parts of the hippocampus can make an individual to experience a loss of memory and a loss of the ability to form new long-term memories.

genetic variation can be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring).