An Unplanned Experiment
In January 1871, a French farmer from Réunion named Heurtin attempted to settle the remote, uninhabited Amsterdam Island. His agricultural plans on the 55-square-kilometer volcanic island failed. After just seven months, Heurtin and his party departed, abandoning their livestock, which included a small herd of five cattle (Bos taurus). This group—likely one bull, two cows, and two calves—became the founding population of a unique evolutionary event. Against all odds, in a harsh environment with relentless winds and limited fresh water, the cattle survived and became feral. The population grew dramatically, reaching an estimated peak of 2,000 animals by the late 1980s. This isolated group provided a rare opportunity to study feralization and rapid adaptation.
Adaptation in Isolation
Over the next century, the Amsterdam Island cattle developed distinct traits. They became smaller than their ancestors, a phenomenon some researchers described as one of the fastest recorded cases of insular dwarfism, with the cattle shrinking to about three-quarters of their ancestral body size. Other studies suggest their small stature may have been inherited from the original breeds. Genetic analysis revealed the founders had a mixed heritage, with about 75% from European taurine cattle (related to the modern Jersey breed) and 25% from Indian Ocean Zebu. This mixed ancestry likely provided a diverse genetic toolkit that aided their survival. The most significant evolutionary changes were neurological and behavioral. Genetic scans reveal that genes related to the nervous system and stress response changed most, allowing the cattle to develop complex social hierarchies and behaviors better suited for a wild existence.
Ecological Impact and Resolution
The success of the cattle came at a high cost to the island's fragile ecosystem. Their grazing and trampling destroyed much of the native vegetation, including the island's unique Phylica arborea trees, which were important for trapping fog and replenishing the island's water sources. The environmental damage threatened the habitats of native species, most critically the endemic Amsterdam Albatross (Diomedea amsterdamensis). The breeding population of this rare bird had been reduced to just five pairs. To save the island's ecosystem, a fence was built across the island in 1987 to confine the cattle to the northern section. Between 1988 and 1989, the 1,059 cattle south of the fence were culled. After studies showed that vegetation recovered in the protected areas, a controversial decision was made to eradicate the entire remaining population. The culling was completed in 2010, bringing the unique evolutionary experiment to an end.