How Did The Giant Sperm Whale Get It's Name?

The "Giant" part is obvious - weighing in at up to 45 tons and reaching sizes of 59 ft (18 meters) it is indeed massive. But why "Sperm Whale"?

Their heads hold large quantities of a substance called spermaceti. Whalers once believed that the oily fluid was sperm, but scientists still do not understand the function of spermaceti. One common theory is that the fluid—which hardens to wax when cold—helps the whale alter its buoyancy so it can dive deep and rise again.

The Giant Sperm Whale also has the largest brain of any creature known to have lived on the face of the Earth. Why didn't anyone think to integrate that fact into his name somehow? Like "The Giant Sharp-Witted Whale", or "Mr. Wise Guy Whale"? But no, it always has to be something about sex, doesn't it.

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