A 2,000-kilometer strip of desert stretching across Namibia is pockmarked with mysterious “fairy circles.” From Angola to South Africa, millions of these bare patches of dirt (which can be seen on Google Earth if you know where to look) dot the landscape, each some five to 10 meters across. And they are not static; they grow and shrink and disappear and reappear.
There have been plenty of ideas about how the fairy circles form. Local legends have attributed the circles to the classic explanations of gods or spirits. Some tour guides more recently have said that a dragon beneath the earth kills the vegetation with his poisonous breath. Some have suggested that various species of insects might be the cause. Others have gone with the ever-popular (though never correct) explanation of aliens. Ask a scientist what causes the fairy circles, and you’re likely to get one of two competing hypotheses: Sand termites remove vegetation and create bare patches, or the circles form as a result of plant competition for the sparse water available in the desert. Under the latter hypothesis, large plants steal water from smaller plants, and this action eventually results in barren spots.
The plant competition argument got a check in its favor last week at the meeting of the Ecological Society of America in Baltimore, Md. Yuval Zelnik of Ben Gurion University in Israel presented data from a simulation that reproduced the birth and death of fairy circles in response to changes in precipitation. In times of drought, when competition for moisture is high, the bare patches grow. When regular rain patterns return, new circles form. In times of heavy rain, when there is plenty of moisture for all the plants, competition lessens and the gaps shrink.
So now we know how fairy circles form, right? Not so fast. Scientists on both sides of the circle have yet to collect enough evidence to convince everyone that either the water competition theory or the termite one is the likely explanation. And researchers are still gathering data. Entomologist Walter Tschinkel of Florida State University, for instance, led a team back to Namibia earlier this year to continue his experiments on the fairy circles; such work may add weight to one of the competing hypotheses — or show that a new one is necessary. That’s how science works.
We often forget that science is a process, not a definitive set of facts. A researcher might spend his or her career pursuing a single hypothesis — and still not confidently land on an answer. Come up with an idea, design an experiment, conduct the experiment, scrutinize the results, wash, rinse, repeat. Scientists publish their findings along the way, and we journalists report them, doing our due diligence to note caveats and use tentative words like “may” and “probably.” But readers might not always pick up on that uncertainty, so that when research contradicts or overturns previous findings, it can look like the royal “science” doesn’t know what it’s doing.The truth is just that science is more difficult and complicated than any single story, or finding, can say.
Science provides a construct for us to explore the world around us. Eventually there will be enough evidence to boldly conclude that fairy circles are probably caused by X. And that “probably” is the important word — it leaves room for being wrong, which is important because even long-accepted scientific theories can get overturned if scientists accumulate the data that will tilt the balance.
The fairy circle tale is a good reminder that we should be more skeptical in general. People need to look at the weight of evidence — not just what one single study, article or person says.
And don’t trust someone who says that they have all the answers — whether they’re a scientist, politician or anyone else — because no one does. This may not be all that important if you’re wondering how fairy circles form, but if you’re going to use science to make big decisions, then it’s good practice.