For years, a handful of researchers have tinkered away at the mystery of Southern Africa's fairy circles, attempting to discover the pixie responsible for the formations. The barren, circular patches of earth freckle a 1,200 mile strip of land stretching from Namibia to Angola, and many of the people working to understand the circles stumbled on them while on vacation. Their origins, however, have proved elusive.
Last year, a paper published in Science declared the problem solved. The author cited termites as the culprits, and many news outlets reported that the case was closed. Other fairy circle aficionados, however, cried foul, insisting that the paper did not provide convincing enough evidence. Here's ScienceNOW:
Vivienne Uys, a termite taxonomist at the Agricultural Research Council in Pretoria, says that [ecologist Norbert] Juergens's findings on the biology of sand termites are consistent with what scientists know about the species. But she says she needs more evidence to be convinced that the insects create fairy circles. "The link between foraging activity of the termite resulting in the formation of a perfect circle of bare soil is unclear."
[Fairy circle researcher Walter] Tschinkel agrees. "Juergens has made the common scientific error of confusing correlation—even very strong correlation—with causation," he says. "If Juergens claims termites are killing the grass, he's got to show that they're actually attacking living plants. That's not easy to do, and he didn't do it."
Now, a paper published in Ecography provides evidence to counter the termite hypothesis.
The authors of this new paper analyzed the distribution of fairy circles over a range of scales. The fairy circles' patterns, they thought, might reflect the processes that created them. So they looked at areas with radii as small as a few feet and as large as 820 (or, in meters, from 1 to 250).
On a large scale, they found that the seemingly random fairy circles in fact occur in regular, homogenized patterns. They compared those findings to other naturally occurring spatial patterns documented in the scientific literature.
The fairy circles' distribution, they discovered, is too homogenized to represent termite colonies, which tend to occur in random clumps. The authors think that, rather than being produced by insects, those formations are the product of natural, self-organizing patterns of plants competing for water and resources in the arid Namib desert. Such phenomena, they found in their literature search, do occur in other parts in the world—just on a smaller scale.
The team also built a process-based computer model, the results of which further supported this hypothesis. The self-organizing hypothesis was also proposed by another paper, published last year in PLoS One.
However, that paper, too, relied on computer models to back up the new hypothesis. As ScienceNOW points out, "To definitively prove the culprit, researchers will need to go into the field and tinker with fairy circle variables such as moisture and soil chemistry." So for now, the mystery is not completely solved—but it is certainly still under debate.