Like humans, dolphins have relatively large brains compared to their body sizes—in fact, dolphins are second only to humans in the ratio between body and brain size. (Related: "Brain Region for Overcoming Fear, Anxiety Found.")



Scientists know that humans need plenty of a sugar called glucose to keep their brains functioning. Some researchers think the same might be true for dolphins, since both species send high amounts of glucose through their bloodstreams.

Dolphins, however, primarily eat fish, which are high in protein and low in sugar. To get enough glucose from this diet, dolphins have evolved a mostly harmless form of insulin resistance, according to Stephanie Venn-Watson, director of clinical research for the U.S. nonprofit National Marine Mammal Foundation.