In the story a male character finds themselves being turned into a caveman. As the transformation happens they will find changes occurring physically and mentally. On the physical side their muscles will grow larger, with their shoulders becoming broader, their arms and legs thicker, and chests wider. They will become much stronger. Their arms will also grow longer and they will find it more natural to lean forward and, eventually, knuckle drag walk with their legs bent and their knuckles dragging against the ground. Their feet will become much bigger, as will their hands. Their bodies will become hairier, with their arms and legs growing hair, their chest becoming hairy, and a their pubes becoming more wild. The male's cock will become MUCH larger and thicker and their balls will also inflate to a larger size. Mentally they will feel their minds beginning to regress. First it will be hard for them to focus. Then they will find it impossible to do things they once did. As it continues their brains will focus on basic needs: Eating, Sleeping, and Fucking. They will become more crude and uncultured. Their speech and thoughts will become more caveman-like, with them speaking in broken sentences and using slower, dumber words to describe things. They will also find the are much happier, no longer burdened with their fears and worries. Modern life will no longer concern them and they will be happy being simple and primal.