There is actually a reason for it. Not a well thought out reason, not a scientifically sound reason — but there was a reason.
One day around 1712, a group of English settlers pushed off the Nantucket coast and set about to harpoon any whale they could find that might be carrying around a decent amount of that highly lucrative blubber. But the sea was angry that day. The whalers got caught up in a Nor’easter, which blew them into much deeper waters in the Atlantic. As a result, they came upon what we now know as a sperm whale, becoming some of the first Westerners to ever capture one.
After a lengthy and presumably pretty disgusting struggle, the whalers were finally able to lift the beast’s head onto the ship, followed by the rest of its body in gigantic chunks. They were surprised to find that its anatomy was very different from any other animal they’d ever encountered. In addition to the fact that the sperm whale has the largest brain mass of any creature on Earth (17 lbs.), the whalers also found an enormous structure atop its skull containing up to 500 gallons of some kind of viscous, off-white, semi-translucent goo.
You see where this is going. Do you see where this is going? You see where this is going.
They speculated that the sticky fluid — “spermaceti,” as it’s still called today — was the whale’s semen, just stored in a very odd location. Which kind of makes sense as an initial theory, although it’s still not totally clear why the whaling community decided to go all in on the “sperm whale” name right away, rather than simply waiting to see what a female looked like or inspecting the rest of the male’s anatomy. In any case, they apparently doubled down on the whole jizz motif, later naming the other weird-goo-filled compartment above the whale’s skull its “junk.”
As it turns out — and as you might have guessed by now — the whalers were wildly wrong in their anatomical speculation. The viscous fluid on top of the whale’s noggin wasn’t reproductive material at all, although we’re still not sure what its exact purpose is, even today. Researchers think it has to do with either echolocation or controlling the whale’s buoyancy, or possibly both.
In any case, the spermaceti material turned out to be a valuable commodity, as it could be processed into an extremely effective fuel source for candles. Its light was particularly white and burned twice as bright as earlier candles. Prior to the advent of the not-terribly-humane sperm oil industry, reading at the twilight of day required a light source made from animal fats that gave off a thick, noxious smoke and didn’t last very long.
Which was a total bummer, so we started hunting sperm whales nearly to the point of extinction. In fact, sperm oil was so sought after as a fuel that it created a near monopoly and one of the earliest examples of price-fixing.
Another weird and kind of gross detail of this story is the fact that whaling ships of the day quickly started assigning their most petite crew members to the job of crawling inside the cavernous space atop the whale’s head to scoop out the spermaceti by the bucket. As Steven Johnson explains in How We Got to Now: Six Innovations That Made the Modern World:
“Extracting the spermaceti was almost as difficult as harpooning the whale itself. A hole would be carved in the side of the whale’s head, and men would crawl into the cavity above the brain — spending days inside the rotting carcass, scraping spermaceti out of the brain of the beast.”
Thankfully, the sperm whaling industry began to decline in the late 19th century with the advent of petroleum as well as electric lamps. Nonetheless, sperm oil continued to be used as a lubricant for car transmissions up until the 1970’s.