In Vanuatu, an island nation in the South Pacific to the right of Australia, people are said to share whole-hog barbecue ahead of winter. They bury an entire pig in the ground and steam it covered with hot stones. It is a dish that celebrities tasted and highly praised on an entertainment show last year. Vanuatu's whole-hog barbecue may be a distant relative of Taiwan's pork jokbal dish.
When scientists decoded pigs' DNA genes, they found that pigs had followed people from Taiwan to Pacific islands starting more than 4,000 years ago. Pigs that spread across Southeast Asia and the Pacific islands are also the subject of the oldest cave paintings drawn by humans. Pigs are like a time capsule that will reveal the human migration process.
◇Spread across Southeast Asia and the Pacific starting 4,000 years ago
An international team led by Laurent Frantz, a professor at Queen Mary University of London, said that over thousands of years, as humans moved to Pacific islands, pigs spread throughout the Asia-Pacific. The paper with the findings was published on the 2nd in the journal Science.
Animals spread to surrounding areas over time. That does not mean they can go everywhere. Alfred Russel Wallace, a British evolutionary biologist, discovered the so-called "Wallace line," a biogeographical boundary between Australia and Indonesia where wild animal ranges do not overlap. Leopards and monkeys are found only on the Asian side to the left of the Wallace line, while marsupials like kangaroos and cassowaries, which resemble ostriches, are limited to Australia and Pacific islands.
Unlike other animals, pigs crossed the Wallace line and spread not only through Southeast Asia but across the Pacific, from Papua New Guinea north of Australia to Vanuatu and Polynesia. To trace the routes pigs took, the researchers decoded the genetic information of 117 modern and ancient pigs spanning 2,900 years and compared it with 585 datasets decoding pig mitochondrial DNA.
Mitochondria are small organelles that produce energy in cells, and unlike the cell nucleus, all their DNA comes from the egg. By backtracking changes in this DNA, one can determine the timing and routes of the maternal ancestors that led to today's pigs. The researchers also analyzed tooth information obtained from 401 modern and 313 ancient specimens to increase reliability.
The analysis found that pigs across the Pacific from the Philippines to Hawaii are descendants of domestic pigs that, starting at least 4,000 years ago, departed with farming communities from southeastern China and Taiwan, moved through Papua New Guinea and Vanuatu, and reached the Pacific islands. The team also confirmed the routes by which Javan warty pigs and Sulawesi warty pigs in Indonesia spread to surrounding regions beginning more than 4,000 years ago.
During the colonial era 200 years ago, European domestic pigs were introduced. In the Komodo Islands, domestic pigs escaped and were found to have hybridized with warty pigs that people had brought from Sulawesi thousands of years earlier. The local hybrids are prey for Komodo dragons, which are now endangered, the researchers said. Pigs brought by humans have thus become part of today's ecosystems.
The researchers said the study raises new questions for wildlife conservation. In some places, pigs have taken deep root in local ecosystems and are regarded as almost native, while in others they are still considered invasive alien species that damage ecosystems. Frantz said, "If we have to preserve native animals, we need to answer at what point we consider them native," and asked, "If humans introduced a species tens of thousands of years ago, are they worth preserving?"
◇A time capsule showing modern human migration
Whether they are alien or native, pigs carry enormous meaning in Southeast Asia and the Pacific. They have already shown the human migration process as the subject of the oldest cave paintings drawn by humans.
A team led by Maxime Aubert, a professor at Griffith University in Australia, announced in 2024 in the journal Nature that the Leang Karampuan cave painting found on Sulawesi, Indonesia, was drawn 51,200 years ago. The image of three people with one wild pig has been recognized as the oldest cave painting and as a hunting scene.
Until then, the oldest cave painting was a 40,550-year-old wild pig image the same team released in 2021 in Science Advances. It was also found in the Leang Tedongnge cave on Sulawesi. Judging from the warts depicted on its face, the pig was estimated to be the island's native Sulawesi warty pig.
Most cave paintings were made with mineral inorganic pigments like ocher, so radiocarbon dating, which uses the organic element carbon, did not work. The Griffith team extracted uranium from calcite crusts formed as water seeped over the paintings. They measured age using the rate at which uranium emits radiation over time and transforms into thorium.
The calcite crusts were found to have formed at least 45,500 years ago. That would make the paintings older than that. But uranium dating has limits: it requires breaking off parts of the painted rock and cannot precisely determine the actual production date of the artwork. In a 2019 Nature paper, the 51,200-year-old cave painting also yielded a uranium date of 43,900 years ago.
In the 2024 paper, the Griffith team said it used a technique to date calcium carbonate closer to the actual pigment layer of the paintings. The rock fragments needed for analysis were only 5 mm, helping to prevent damage to the art. Using the new method, the team estimated that the pig image in the Leang Karampuan cave painting was drawn at least 51,200 years ago.
"The recent discoveries support the claim that cave art did not originate in Ice Age Europe, as long thought, but began earlier in the course of human migration," the Griffith team said, adding, "Modern humans likely left Africa, passed through Southeast Asian islands, and reached Australia 65,000 years ago." Pigs preserved in the paintings later evolved from prey into livestock and followed humans to remote Pacific islands. Humanity truly seems to have found a pig of good fortune.
References
Science(2026), DOI: https://doi.org/10.1126/science.adv4963
Nature(2024), DOI :https://doi.org/10.1038/s41586-024-07541-7
Science Advances(2021), DOI: https://doi.org/10.1126/sciadv.abd4648
Nature(2019), DOI: https://doi.org/10.1038/s41586-019-1806-y