Thank you for your thoughtful comment and for pointing out a potential blind spot in my story. You are correct in highlighting that not all humans made migrations to colder climates, which indeed suggests that not all individuals would necessarily have developed the fructose/uric acid infirmity as a result. I appreciate your perspective and will write a story about it. But my point in that short sentence is that anthropologists observed this genetic mutation for the first time when our ancestors started migrating from Africa to Europe continent. It is a long and complex topic, so it is not possible to mention it in that story; therefore, I encapsulated it to give a quick clue about its origin. There are several other factors like dietary and lifestyle changes of our early ancestors for losing this capability.