If sperm whales can capsize boats, it is due to their large forehead filled with a substance once mistakenly called "false sperm." What the American novelist Herman Melville described in Moby Dick is now explained scientifically. The whale's forehead is capable of delivering a fatal blow to a rival or even a large boat. To write Moby Dick, Herman Melville was partly inspired by real events. As the BBC explains, the New York writer was notably based on the wreck of the whaling ship Essex, which occurred on November 20, 1820. According to the account given fifty years later by Thomas Nickerson, who was 15 years old at the time, a first whale pierced the ship's hull. Then another, larger one, charged at the ship. The violence of this impact was so great that all the men were thrown to the ground. After moving away a few hundred meters, the cetacean turned around and came back at full speed, this time breaking the bow of the whaling ship. Result: the ship sank. If this may seem very romantic, science has nevertheless shown that some cetaceans are indeed capable of causing shipwrecks. Moreover, it has even managed to understand where this ability comes from: 1,900 liters of spermaceti. In fact, everything happens in the head of the mammals, which represents about a third of their total length. Weighing up to 9 kilograms, their brain is the largest of all land animals. But the main action takes place at the level of the forehead: sperm whales have a large fatty and soft organ called spermaceti, which is unique to their species. Filled with a fatty substance also called spermaceti, it got its name because whalers long thought it was sperm. The volume of this liquid is impressive, as it can reach 1,900 liters. As early as the 18th century, some whalers — and notably Owen Chase, the second officer of the Essex — claimed that the forehead of the sperm whales constituted their main weapon. "We decided to check it," explains Dave Carrier, an evolutionary biologist now retired. He estimates that if this theory has long been ignored, "the intuition and experience of the whaler were probably correct." In a study published in 2022, Dave Carrier suggested that the forehead of the sperm whale had evolved to become a kind of ram, capable of delivering a fatal blow to a rival, like the hippopotamus. "Sperm whales are mammals, close relatives of deer and rams, among which males compete by colliding. This behavior could therefore be inherited from their ancestors." Another study, dating back to 2015, indicates that this organ has sufficient shock absorption capacity for whales to use it without risk of injury. Alec Burslem, an ecophysiologist at the University of Hawaii, has observed this behavior several times in young sperm whales. He was even able to record some impacts. According to his calculations, an adult large sperm whale is likely capable of exerting a force equivalent to a collision with a bus traveling at 65 km/h. The BBC takes the opportunity to recall that there are other theories about the role of spermaceti, which could well have multiple functions. Sperm whales do indeed produce sounds through "monkey lips," a pair of vocal lips located at the front of the nose. In water, these sounds propagate both forward and backward, up to the terminal wall of the spermaceti, at the back of their head. According to Alec Burslem, when a female hears the combination of these two sounds, she can assess the size of the male's spermaceti and determine whether it is a large specimen with which she would like to mate.