In the 1700s, there was a naturalist in Switzerland who studied hibernating animals. Conrad Gessner found an organ between shoulder blades that looked like brown fat. A researcher at UCLA later discovered it's made out of fat and has been used to study human tumors. When babies are born, there's a little lump of brown fat that actually is there. It serves a function because it harbors gut microbiome - which we know now can help fight cancer.