Once a year, adult male Asian and African elephants go through musth, or a period when their reproductive hormone levels—including testosterone—surge, and they act more aggressive and unpredictable.
Paleontologists have long wondered if male woolly mammoths—modern elephants’ extinct relatives—also experienced this condition, which appears to have a breeding purpose. Now, thanks to a cleverly designed study, published Wednesday in the journal Nature, researchers at the University of Michigan have uncovered evidence that suggests mammoths also went through musth when they roamed the Earth during the Pleistocene and Holocene epochs.
Mammoth and elephant tusks are like tree trunks in that they grow in concentric rings and, in the process, capture information about an animal’s diet, lifestyle and condition throughout its lifetime. As Ashley Strickland writes for CNN, they’re like “time capsules.” This information is stored in layers of dentin—the material that’s in all teeth, as tusks are elongated upper incisors. Dentin can contain valuable endocrine data, or traces of hormones, and it doesn’t easily degrade, making it a prime contender for studying the lives of animals, even very old ones.
Armed with this knowledge, scientists suspected that mammoths’ tusks might hold the answer to the musth question. To that end, they took samples from various points along the tusks of an adult male African elephant killed by a hunter in 1963, a male woolly mammoth that lived between 33,291 to 38,866 years ago and a female wooly mammoth that lived between 5,597 to 5,885 years ago, according to a statement. Then, they analyzed the samples, isolated the hormone levels in each one and compared them across time and with one another.
As expected, the female wooly mammoth’s testosterone levels changed very little throughout her life. But both male animals experienced big fluctuations of the hormone: The analysis of the African elephant’s tusk showed its testosterone levels increased to 20 times higher than normal during musth. The male wooly mammoth, meanwhile, periodically experienced testosterone levels ten times higher than normal, which the researchers concluded meant the extinct animal also went through musth.
Susan Alberts, a biologist at Duke University who was not involved in the project, considers the experiment an “exciting and fascinating piece of scientific sleuthing,” as she says to New Scientist’s Riley Black. “The comparison of the elephant and mammoth tusks is compelling evidence that they are picking up the same signals in the two species.”
The results themselves were not a shock. However, the researchers were somewhat surprised—and excited—that their tooth-hormone methodology provided such clear-cut evidence for mammoth musth. When study co-author Richard Auchus, an endocrinologist at the University of Michigan, first saw the results, it was “pretty black-and-white what was going on,” he tells Ars Technica’s Jeanne Timmons.
“There are few times in my scientific career when I’ve been just floored with a piece of data,” Auchus tells the publication. “I never thought we’d be able to see the testosterone changes with such clarity.”
There’s still a lot that researchers don’t know about musth, which comes from the Urdu and Hindi word for “intoxicated.” Similar to the rutting period that deer, elk and other ungulates go through, elephant musth is associated with more frequent or near-constant urination, changes to the fluid secreted from the glands on the animals’ temples and erratic behavior. As Caitlin O’Connell-Rodwell wrote for Smithsonian magazine in 2010, elephants in musth appear to be sending a message to other males along the lines of “don’t even think about messing with me ’cause I’m so crazy-mad that I’ll tear your head off.” Musth appears to be related to sexual selection, as past research has found that female elephants prefer to mate with males in musth.
Moving forward, the tusk analysis technique used in the new study could prove useful for an array of applications in zoology and paleontology. For instance, studying the hormones in the teeth of mammoths and other extinct animals could potentially reveal pregnancies or stressful moments in the creatures’ lives. Researchers might also be able to analyze dentin samples from modern and ancient hominids to understand “reproductive ecology, life history, population dynamics, disease and behavior in modern and prehistoric contexts,” the researchers write in the paper.
Researchers are also curious whether changes in musth over time could offer clues about what contributed to mammoths’ demise and eventual extinction roughly 4,000 years ago. Would hunting by humans or changes to the climate, for instance, have altered their testosterone surges, which would then show up in their teeth? While this and many other questions remain unanswered, for now, scientists have gleaned a bit more knowledge about the mysterious lives of these giant, hairy creatures.