33,000-year-old wooly mammoth tusk confirms testosterone-driven aggression in elephants

"Temporal patterns of testosterone preserved in fossil tusks show that, like modern elephants, mature bull mammoths experienced musth," said Michael Cherney, lead study author, and a researcher and a researcher at UM Medical School, in an official release.

The tusk is a promising source of information 

Generally, scientists study increased testosterone levels during musth in modern elephants from their urine and blood samples. When it comes to mammoths, their injured remains and damaged tusk tips serve as hints of the musth battles in ancient times. 

Authors of the current study argue that tusks can be used as a reliable resource for studying hormone levels during musth in both modern and ancient elephants. This is because when an elephant is alive, new growth layers keep on adding naturally to its tusk throughout its life. These growth layers have information related to physiological, environmental, and hormonal changes that the animal experiences.

This information stays preserved in dentin, one of the hardest bony tissues found in a mammal’s body. The records in dentin can be used by scientists to track the hormonal changes a mammoth or elephant experiences throughout its lifetime.      

"This study establishes dentin as a useful repository for some hormones and sets the stage for further advances in the developing field of paleoendocrinology. In addition to broad applications in zoology and paleontology, tooth-hormone records could support medical, forensic, and archaeological studies," said Cherney.

Dentin is also found in the teeth of other mammals including humans. Currently, hormone levels in humans and animals are examined using bone, hair, or nail samples. However, these methods are not widely accepted and raise several doubts.

The current findings suggest that since teeth remain preserved for a long time like tusks, they could act as a reliable and long-lasting source of information on steroid hormone levels in other mammals as well.

The study authors note, "With reliable results for some steroids from samples as small as 5 mg of dentin, these methods could be used to investigate records of organisms with smaller teeth, including humans and other hominids."

Comparing musth in woolly mammoth and modern elephant

During the study, the UM researchers analyzed three tusk samples; the first sample was from Siberia and it belonged to a woolly mammoth (Mammuthus primigenius) that lived between 38,866 to 33,291 years ago.

The second tusk was of an adult African bull elephant (Loxodonta africana) that died in 1963, and the third sample was from a female woolly mammoth that survived between 5,597 to 5,885 years ago.

The CT scan results revealed that during musth, testosterone levels were 10 and 20 times high in male woolly mammoth and African elephants respectively. The researchers believe that low levels in woolly mammoth may be due to a higher degradation of its tusk sample. 

On the other, the level of testosterone well as other hormones such as progesterone in the female woolly mammoth didn’t show any significant variation during its lifetime. 

Another interesting aspect of the study is that the researchers had to develop novel methods to perform this one-of-a-kind tusk analysis. 

"We had developed steroid mass spectrometry methods for human blood and saliva samples, and we have used them extensively for clinical research studies. But never in a million years did I imagine that we would be using these techniques to explore 'paleoendocrinology,'” said Richard Auchus, one of the study authors.

Hopefully, this research work will uncover new ways of studying life history, biology, hormonal changes, and diseases in detail in both modern and ancient mammals.  

The study is published in the journal Nature.

Study Abstract:

Hormones in biological media reveal endocrine activity related to development, reproduction, disease and stress on diferent timescales1 . Serum provides immediate circulating concentrations , whereas various tissues record steroid hormones accumulated over time. Hormones have been studied in keratin, bones and teeth in modern5–8 and ancient contexts; however, the biological signifcance of such records is subject to ongoing debate, and the utility of tooth-associated hormones has not previously been demonstrated. Here we use liquid chromatography with tandem mass spectrometry paired with fne-scale serial sampling to measure steroid hormone concentrations in modern and fossil tusk dentin. An adult male African elephant (Loxodonta africana) tusk shows periodic increases in testosterone that reveal episodes of musth17–19, an annually recurring period of behavioural and physiological changes that enhance mating success20–23. Parallel assessments of a male woolly mammoth (Mammuthus primigenius) tusk show that mammoths also experienced musth. These results set the stage for wide-ranging studies using steroids preserved in dentin to investigate development, reproduction and stress in modern and extinct mammals. Because dentin grows by apposition, resists degradation, and often contains growth lines, teeth have advantages over other tissues that are used as records of endocrine data. Given the low mass of dentin powder required for analytical precision, we anticipate dentin-hormone studies to extend to smaller animals. Thus, in addition to broad applications in zoology and palaeontology, tooth hormone records could support medical, forensic, veterinary and archaeological studies.