Seals and whales are able to dive underwater for extended periods of time because they are able to better store oxygen in their systems. While humans store 36 percent of their oxygen in their lungs and 51 percent in their blood, seals store only approximately 5 percent of their oxygen in their lungs and 70 percent in their blood. They also store more oxygen in the muscle tissue—25 percent compared with only 13 percent in human muscle tissue. While underwater, these mammals’ heart rates and oxygen consumption rates decrease, allowing some species to remain underwater for up to twenty minutes at a time.

In 2013, researchers finally uncovered how diving mammals evolved their underwater endurance. They found that marine mammals, such as the sperm whale, all have high concentrations of oxygen-binding protein called myoglobin—the protein that gives red meat its color—in concentrations so high that the muscles of these mammals are almost black in color. The scientists knew that the protein tends to stick together in such high concentration and cuts down on their function to carry oxygen. They found that deep-diving mammals—and even aquatic mammals such as beavers—had more of an electric charge on the surface of their myoglobin. The researchers further speculated that such an electric charge causes “electro-repulsion”—similar to trying to put two magnets with the same pole together (it’s not possible)—thus preventing the stickiness of the protein in the mammals and allowing for more oxygen in their muscular systems for those deep, long dives.