Evolution. Starfish also (generally) have 5 arms, so 5 is something that appeared fairly early on. That 5 could just as easily been 4. Look at Disney animals,

Evolution. Starfish also (generally) have 5 arms, so 5 is something that appeared fairly early on. That 5 could just as easily been 4. Look at Disney animals, they usually have 3 fingers and a thumb and seem to get along just fine.