Text copy of the article
The two massifs that make up the bulk of New Zealand – the North Island and the South Island – are less than 25 kilometers apart but they couldn’t be more different. The North Island hosts Auckland, the country’s largest city, and is known for its towering volcanoes, legendary surfing beaches, and relatively mild climate. In the cooler and quieter South Island, rugged landscapes are pierced by glassy lakes, glaciers and snow-capped mountains – familiar backdrops for fans of Lord of the rings movie trilogy. Recent research reveals that the differences between carrots extend all the way back to the rodents. The findings could change our understanding of history.
It all began two decades ago, when zoologist Caroline King and one of her students were unraveling the origins of invasive rats in New Zealand through genetic analysis. As expected, the researchers found that the North Island house mice are descended from European mice that walked on the ships of British colonists two centuries earlier.
But when King and her team analyzed South Island rats, they discovered that the animals were related to a rat from Southeast Asia, a subspecies common in China but not found outside Asia. Stray rats baffled King, who works at the University of Waikato in New Zealand. “We couldn’t think of where they came from,” she says.
The rodent mystery deepened in 2019, when researchers at New Zealand’s University of Auckland discovered the same tendency in Norway rats. The South Island rats correspond to a breed known only from China, while the North Island rats are the closest to England.
Mounting evidence suggests that rats and mice traveled from China to the South Island in the 19th century, when New Zealand was still part of the British colony of Australia. But there were no historical records – at least in English – of direct contact between China and the South Island that would explain how the rodents arrived. King began to suspect that the rodents’ traveling conditions were not perfect.
In 2022, King co-authored a study that offers a tantalizing explanation: the lemmings arrived with traders who sailed to China to illegally sell New Zealand fur seal pelts, and then returned to the South Island. In the 19th century, plentiful fur seal deposits dotted the rugged coast of the South Island, and leather was the only profitable commodity on the island. And in Canton (present-day Guangzhou), a bustling port city in southern China that formed the backbone of international trade, fur seal skins gained value as sea otters were rare in the world and their valuable fur. Those daring enough to skirt the rules by hunting fur seals could make a fortune.
At the turn of the nineteenth century, conditions were ripe for shady dealings to flourish. The profit-hungry British East India Company tightly controlled its monopoly on maritime trade by forbidding the colony from doing direct business with China and India. Most of the official merchant ships from London, England, stopped in Sydney, Australia, on their way to supply New Zealand’s main port on the North Island.
King theorized that unscrupulous fur traders passed Sydney on their way to and from Canton to avoid the authorities. “Those who wanted to bypass the regulations did so very calmly,” she says. Such clandestine trips would also have escaped official record-keeping.
To determine whether the invading rodents arrived in the South Island on official flights, or via a clandestine shipping route directly from China, King and her colleagues compared the rodents’ DNA with genetic material from 19th-century mice and mice samples discovered near Sydney Harbour.
The results reinforced King’s suspicions. The Sydney house mice had European ancestry and the mice’s genes matched those of the Norway rats found in Britain and the North Island. There was no trace of the genes of the Southeast Asian domestic rat or of the Chinese rat strain – evidence that ships carrying the rodents from China did not pass through Sydney. Or most of them didn’t.
There is some evidence of nefarious dealings across the port, says Philippa Main Smith, a historian at the University of Canterbury in New Zealand who was not involved in the research. In 1806, Simeon Lord, a former businessman and sealed businessman based in Sydney, was caught by colonial authorities for shipping 87,000 sealskins collected in the Antipodes Islands, south of New Zealand, to Canton via Sydney. But by some small miracle, Lord’s journey must have left no ferrets to waste.
Rogue merchants who evaded detection by avoiding official shipping routes would never suspect that the genes of disguised mice and rats could reveal their movements centuries later. “the [rodents] says King.
King’s conclusion is plausible, says Main Smith, given that many Sydney merchants were at least as dodgy and profit-hungry as Lord’s. “There were all kinds of hidden deals going on,” she says.
Although historians had an idea of a secret trade in fur seal pelts between Australia and China, the paucity of historical evidence made it difficult to confirm.
Genetic evidence can reveal information about the past that cannot be found in historical records or accounts, says study co-author Andrew Veale, a vertebrate pest ecologist and geneticist at Manaaki Whenua Landcare Research. “DNA has this ability to tell the story of what really happened.”