A mysterious organ in the sperm whale's head gives it the power to sink ships

A survivor of the shipwreck that inspired the novel Moby Dick had a theory about how a sperm whale could destroy a vessel many times its size – 200 years later, he's been proved right.

On the morning of 20 November 1820, 15-year-old Thomas Nickerson had just escaped from one whale punching a hole in the side of his boat. Rowing quickly back to the main whaling ship as the boat took on water, Nickerson and his companions thought they were safe.

But, taking the helm of the whaleship Essex, Nickerson saw another, much larger whale speeding straight towards them. Alerting Owen Chase, the ship's first mate, there was shouting and alarm among the crew followed by "a tremendous crash", Nickerson wrote 50 years later. 

The whale struck the Essex with such force that all the men were knocked off their feet. The whale swam 900ft (270m) away from the boat, turned around sharply and came back at its utmost speed. With that second collision, it stove in the entire bow. The whaleship Essex was sunk. 

If it sounds like a novel, it's because the shipwreck of the Essex inspired Herman Melville's Moby Dick. Today, 175 years after publication of the book, research has revealed the mystery of how a sperm whale can take down a ship several times its size. As it turns out, the answer was correctly predicted more than 200 years ago by none other than Chase, the first mate of the Essex. 

Ironically, the whales' superpower seems to reside in the same place as the precious oil chased by the whalers: inside its head.

Sperm whales have a huge head. In fact, their heads make up around a third of their overall body length. Weighing up to 9kg (20lbs), they boast the biggest brain of all animals on Earth.

Within the forehead is a large fatty, squishy organ called the spermaceti – unique to their species. This organ is filled with an oily substance also called spermaceti, which gained its name because whalers thought it was semen.

The spermaceti was highly sought after by whalers as the oil provided a high-quality fuel, and could be congealed into products like soaps and candles. During the 18th and 19th Centuries, around 300,000 sperm whales were killed worldwide.

Despite this extensive harvesting of the sperm whales' spermaceti, we still don't fully understand its function.

One theory sees the spermaceti as a combat tool.

"This wasn't originally our hypothesis, it was Owen Chase's", says retired evolutionary biologist Dave Carrier. "An 18th-Century whaler argued that the forehead was a weapon, and we set out to test that."

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For the past two centuries, biologists had largely ignored Chase's ideas, but from Carrier's perspective, "the whaler's intuition and experience were probably correct". 

In a 2002 study, Carrier suggested that the sperm whale's greatly enlarged melon – a fatty organ located in the forehead of all toothed whales – evolved as a battering ram, able to deliver a fatal blow on a rival, just like a hippo. "Whales are mammals, closely related to animals like deer and rams, where males compete by ramming – so this behaviour may be inherited from their ancestors."

Recently, Alec Burslem, an ecophysiologist at the University of Hawaii, caught sperm whales on camera while they were head-butting not a whaling ship, but each other. It was "a lucky coincidence" he captured the behaviour, he says, which took place around the Balearic Islands and the Azores.

It might seem strange that whales would use their head to fight – why would anyone endanger a vital body part to hit an adversary? But a 2015 study says that the organ has enough buffering that whales could use their head as a ram without risking damage.

Burslem observed this behaviour multiple times, by a number of young sperm whales. The biggest impact he recorded was made by a juvenile male who sped towards another whale at 15ft per second (4.5m per second) and hit its companion with a force of about 460kN. Burslem estimates a large fully-grown sperm whale closing in at the same speed would hit with a force of approximately 1,200kN – that would feel like being hit by a bus travelling at 40mph (65km/h).

Turned on a ship, this is a considerable force.

"In history, only three whaling ships were attacked by whales," says Michael Harrison, chief curator at the Historical Society in Nantucket, which hosts an impressive collection of original logbooks and artefacts. But whales would routinely attack the smaller, open boats that were lowered overboard from the main ship when a whale was spotted.

"The logbooks don't often do justice to the drama of this," says Harrison.

In all three cases when a whale attacked the mother ship, the attacker was a sperm whale. In 1851, in the South Pacific, a sperm whale charged the Ann Alexander and completely wrecked it. In 1902, too, a sperm whale wrecked the Kathleen, which was sailing off the Galapagos Islands. But it was the fate of the Essex that became perhaps the most infamous survival ordeal in maritime history. 

That day, 20 men abandoned the sinking mother ship and clambered onto three whaleboats. They were 1,300 miles from land and what followed became one of the most gruesome stories in maritime history, and inspiration for Melville's Moby-Dick.

Of course, we don't know how often sperm whales use their heads as battering rams in nature, when no drone is watching, says Burslem. Neither do we fully understand the purpose of their uniquely enormous melon. 

There are other theories on the role of spermaceti, and it may have more than one use. Whales produce sound with "monkey lips", a pair of phonic lips located at the front end of the nose. The sound travels both forwards into the water and backwards, to the end wall of their spermaceti at the back of their head. 

When a female hears the combination of these two sounds, she can judge how big the spermaceti of the male is, and whether it is a large specimen she'd like to mate with, says Burlsem.

"We have a huge amount still to learn about these animals. We need to prioritise keeping them around, " says Burslem. "We're really only just starting to understand."

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