The Origins of the Arctic Fox

The arctic fox lives in the far northern Arctic region with other well-known arctic animals like the caribou, musk ox, and polar bear.Scientists aren’t sure exactly when the arctic fox first evolved. Arctic fox bone fragments from the Pleistocene epoch (2.6 million-11,700 years ago) are rare, and the ones that do exist are difficult to date with any degree of accuracy. The oldest confirmed arctic fox bone is believed to be 200,000 years old. There are other bones that may be 400,000 years old, but whether they belonged to an arctic fox or some other fox remains under debate. “It’s still an open question,”says Love Dalen,a Swedish biologist who has been using genetics in an attempt to understand the evolution of the arctic fox. “Right now the best estimate is that arctic foxes emerged somewhere between 200,000 and 400,000 years ago, presumably during one of the ice Ages.”

For many years researchers believed the species arose in Europe,basing this conclusion on the location of those 2000-year-old fossils. Since the early 1980s, however, genetic comparisons between different fox species have revealed some surprising results. For example, research done by Robert Wayne at the University of California at Los Angeles has found that the arctic fox, despite its unique appearance and adaptations, is actually much more closely related to other foxes than had previously been thought. Its closest living relative, according to the genetic studies, is the North American swift fox.

The result suggests one of two scenarios. One is that arctic foxes gave rise to swift foxes, an evolutionary sequence that would depend on the arctic fox being much older than the fossil record currently indicates. The second possibility is that swift foxes gave rise to arctic foxes, likely during the height of a period of glaciation when tundra forming to the south of the ice sheets may have met the grassland habitat of the swift fox.

On the one hand, the latter scenario could hardly seem more implausible. Swift foxes, after all, live on the arid, sun-baked prairies and open desert, where temperatures can top 120°F (49°C). It’s hard to imagine a greater environmental leap from this environment to the frozen tundra. To have acquired over the course of a few hundred thousand years all the adaptations necessary for survival in such an extreme environment suggests a rapid rate of evolution. And for the early species to have so rapidly conquered such a large territory in a polar region seems equally mystifying.

In other ways, however, this scenario works. As one of the smallest foxes, the swift fox can survive on very little food, a trait that would have helped its ancestors gradually stray farther and farther into the biologically barren tundra. And being a nocturnal hunter that seeks shelter in a den during the day, the swift fox is not overly adapted for life at high temperatures. Indeed, in the northern parts of their range, modern swift foxes have faced winter temperatures every bit as severe as those encountered in the Arctic.

From what researchers know about the evolution of other polar species, there seems to be a pattern of evolution in which species living in the biologically rich temperate zone give rise to animals that are more specialized for survival in the more extreme Arctic. Polar bears, for instance, are thought to have evolved from a northern population of brown bears that learned to hunt seals out on the sea ice. As for the rapid evolution and widespread dispersal, one must remember that the arctic fox is no ordinary species when it comes to both reproductive efficiency and migratory tendency; rapid genetic change and rapid migration would both appear to be well within the species’ capabilities.

According to Love Dalen, most of the arctic species evolved during the Quaternary Period (the last 2.6 million years) and they all seem to have evolved from temperate species. In evolutionary terms, arctic species are quite young, including, presumably, the arctic fox. Dalen adds that if that is true, then the arctic fox would have evolved in North America, though he notes that there is no solid proof either way.

1.The arctic fox lives in the far northern Arctic region with other well-known arctic animals like the caribou, musk ox, and polar bear.Scientists aren’t sure exactly when the arctic fox first evolved. Arctic fox bone fragments from the Pleistocene epoch (2.6 million-11,700 years ago) are rare, and the ones that do exist are difficult to date with any degree of accuracy. The oldest confirmed arctic fox bone is believed to be 200,000 years old. There are other bones that may be 400,000 years old, but whether they belonged to an arctic fox or some other fox remains under debate. “It’s still an open question,”says Love Dalen,a Swedish biologist who has been using genetics in an attempt to understand the evolution of the arctic fox. “Right now the best estimate is that arctic foxes emerged somewhere between 200,000 and 400,000 years ago, presumably during one of the ice Ages.”