It doesn't need to be the tradition that shaped our biology. It could be our biology that shaped the tradition. Assuming we already have some benefit to fasti

It doesn't need to be the tradition that shaped our biology. It could be our biology that shaped the tradition. Assuming we already have some benefit to fasting, a group who make a tradition of fasting are more likely to survive than a group who does not. Thus the fasting meme takes over as the people who believe in it take over.