It sounds like something straight out of an adventure novel. A piece of buried treasure on a sunken ship leads a group of intrepid researchers to a groundbreaking discovery with modern-day implications.
But this is no fiction. In a study published Thursday in Current Biology, researchers describe a trove of shipwrecked ivory, lost to time hundreds of years ago. From these historic elephant tusks, the researchers reveal not only the origin of these 16th-century elephant remains, but also new information about the Elizabethan ivory trade, and how the trade continues to affect the lives of animals today.
Here's the background — In 2008, the Portuguese trading ship Bom Jesus — the oldest-known shipwreck off the coast of southern Africa — was discovered, lying on the seabed near Namibia.
Hidden amongst the forty-ton plunder of gold and silver coins on board were 100 elephant tusks. Ivory tusks are essentially huge teeth, which protrude from elephants' mouths. Now, the ivory trade is done on the black market. But it was once a hot commercial product, leading to the over-hunting of elephants and other creatures.
What's new — The key to the study is the analysis of genetic material preserved in the tusks. DNA analysis can reveal hidden details about an elephant's life — where it came from, what kind of environment it lived in, and what it ate. The ivory trove is hundreds of years old, but it is only with this modern-day technology that researchers can piece together what actually happened to these elephants.
How they did it — The reason why the tusk DNA is so rich in knowledge is partially to do with elephants' behavior. Female elephants tend to stay with their herds in relatively limited geographic areas, not venturing too far afield. Mitochondrial DNA, passed from mother to offspring, can reveal where each individual came from. In this case, the ivory appears to have come from elephants which once lived in Africa.
By comparing the tusks' DNA with reference data, the researchers found matches with forest elephants in West Africa. Next, they conducted an isotope analysis of the ivory to learn more about the elephant's diet and further confirm its origins.
"We analyzed the stable isotope ratios of carbon and nitrogen in the tusks, as these elements come from drinking water and plant foods that the elephant eats," Ashley Coutu, a co-author on the study from the University of Oxford, tells Inverse.
"Knowing about an elephant's food and water sources gives us clues about their habitat and where they originated."
Fun fact: elephant tusks grow throughout their lifetime. By taking multiple samples from a single elephant tusk, the researchers were able to determine "seasonal variation in the diet," according to Coutu.
"This elephant ate more grass on a seasonal pattern, which is the same pattern we see in elephants living in savanna and mixed woodland habitats today," Coutu says.
Why it matters — Discovering the origins of these 16th-century animals can help scientists better understand how the range of modern-day elephants is similar to that of these ancestral populations.
"Today, some West African forest elephants live outside of the tropical rainforest; these results show that West African forest elephants have been living outside of tropical forest for hundreds of years," Coutu says.
One of the most unexpected findings in the study is that modern-day elephants appear to lack some of the haplotypes found in their 16th-century predecessors.
The reason why may have to do with elephant conservation. The population of West African elephants has declined by 90 percent since the 16th century, according to Alfred Roca, a co-author on the study from the University of Illinois at Urbana-Champaign.
"These sample show a higher degree of genetic diversity than has been detected in modern-day West African forest elephants. This suggests that the ivory trade removed much genetic diversity from the population in West Africa," Roca says.
Digging into the details — The study also helps fill in the gaps in the history of global trade, include how the ivory trade linked far-flung nations via specific trading networks.
The Bom Jesus, for example, set sail from Lisbon on an Indian trading route — but the study establishes connections between the Portuguese capital and West Africa as far back as the 1530s. Ultimately, it reveals the extent of human trade, long before the age of globalization.
The researchers hypothesize the ivory tusks came to be on the Bom Jesus via a Portuguese trading post known as São Jorge de Mina (Elmina) on the southwestern edge of the Dahomey Gap. Guinean forests and savannah surround that area.
The study states:
Analyzing historic and archaeological ivories affords a window into human-animal relationships across thousands of years and can reveal the formative and changing patterns of exchange between people who lived oceans apart.
What's next — The tusks may be 500 years old, but the study's findings may be able to help law enforcement officials targeting illegal poaching of ivory today. The reason is the DNA in the tusks — with it added to the reference bank of DNA from West African elephants, it becomes more possible to trace any subsequent ivory finds to this region or other areas of the world.
The researchers previously developed software from mitochondrial elephant DNA samples, allowing them to analyze DNA sequences and place them on a map of Africa where similar sequences have been reported.
"There are a limited number of sequences from West African elephants, and the ivory has increased the number of sequences available from this region," Roca says.
"If the DNA in confiscated poached ivory matches the sequences found in the shipwreck ivory, that would be an indication that the modern day poaching had occurred in West Africa," he adds.
"This allows law enforcement and forensics labs to examine where the elephant ivory may have originated," Roca says.
Abstract: The oldest known shipwreck in southern Africa was found in Namibia in 2008.1–4 Forty tons of cargo, including gold and silver coins, helped identify the ship as the BomJesus, a Portuguese nau (trading vessel) lost in 1533 while headed to India.4–6 The cargo included >100 elephant tusks,7 which we examined using paleogenomic and stable isotope analyses. Nuclear DNA identified the ivory source as African forest (Loxodonta cyclotis) rather than savanna (Loxodonta africana) elephants. Mitochondrial sequences traced them to West and not Central Africa and fromR17 herds with distinct haplotypes. Four of the haplotypes are known from modern populations; others were potentially lost to subsequent hunting of elephants for ivory. Stable isotope analyses (d13C and d15N) indicated that the elephants were not from deep rainforests but from savanna and mixed habitats. Such habitats surround the Guinean forest block of West Africa8 and accord with the locations of major historic Portuguese trading ports.9,10 West African forest elephants currently range into savanna habitats;11–13 our findings suggest that this was not consequent to regional decimation of savanna elephants for their ivory in the 19th and 20th centuries. During the time of the Bom Jesus, ivory was a central driver in the formation of maritime trading systems connecting Europe, Africa, and Asia. Our integration of paleogenomic, archeological, and historical methods to analyze the Bom Jesus ivory provides a framework for examining vast collections of archaeological ivories around the world, in shipwrecks and other contexts.