I am convinced it is hereditary. I got the genes from both sides of my family as both of my grandfathers were exceptionally huge as was my father, his two brothers, uncles, and cousins, and my mothers brothers, uncles and cousins. I am the oldest son of my father and my younger brothers are also huge, along with the five cousins I know about. I have other cousins, but I have no idea and have seldom seen them, and most I have not seen in decades.