Devin O'Branagan, Author

The dog exists because Ice Age hunters could not live on lean meat. Wolves and people wanted the same animals, and for a long time nobody could explain why a band of hunters would feed a rival through a winter. In 2021 a team of Finnish researchers did the sums for the coldest stretch of the last Ice Age and found the answer in the human liver. By late winter a reindeer or a horse has burned through its fat and is nearly all muscle. A person can only clear so much protein. Push it much past a third of what you eat and you get sick, then weak, then worse, however full your stomach is. So a hunting band took what it needed, the marrow, the brain, the tongue, every scrap of fat, and was left sitting on a heap of lean meat it could not safely finish. A wolf can live on lean meat for months. The surplus went to the pups by the fire. Nobody was competing for it. A few thousand winters of that and you have a dog. So the oldest friendship on earth rests on one fact about your metabolism: you are the fat-eater in the partnership. Your ancestors dealt with the skinless chicken breast twenty thousand years ago by throwing it to the wolf. Today the lean cut is on your plate with a health sticker on it, and his descendant gets a brown biscuit made of maize. He was better fed in the Ice Age. So were you.