The purpose of Mesoamerican potbelly statues have been the subject of debate among anthropologists for decades: Are they depictions of the ruling elite? A way to honor dead ancestors? Or perhaps portrayals of women giving birth?

As the various theories wound their way through academic circles, the surprising discovery four decades ago that many of the statues, found in Guatemala, are magnetized in certain spots added a new dimension to those discussions.

And a Harvard study suggests that where those areas show up is no accident.

Led by Assistant Professor of Earth and Planetary Sciences Roger Fu, a team of researchers has shown that artisans carved the figures so that the magnetic areas fell at the navel or right temple — suggesting not only that Mesoamerican people were familiar with the concept of magnetism but also that they had some way of detecting the magnetized spots. The study is described in an April 12 paper published in the Journal of Archaeological Science.

“Our direct observation is that there are magnetic anomalies consistently on certain features of these sculptures,” Fu said. “And the question we asked is whether this is consistent with random chance, or does it require some knowledge or some awareness of where those anomalies are?

“There’s some chance it could happen randomly, but as we find more and more sculptures that are aligned like this, the smaller than likelihood is,” he continued. “In this paper, we looked at four, and we found a less than 1 percent chance that this wasn’t intentional.”

A close study of the anomalies, Fu said, showed they could only have been caused by one source — lightning.

“All rocks contain magnetic minerals,” he said. “If you go outside and pick up any random rock, it is magnetic. It’s just very, very weakly magnetic. These rocks are basalts from the highlands of Guatemala, and they happen to contain quite a bit of magnetite, as well as other magnetic minerals.”

Rocks typically become magnetized as they cool, and minerals like magnetite, hematite, and iron sulfides become aligned with Earth’s magnetic field. While that process can create detectable magnetic fields, Fu said they are usually not even strong enough to move a compass needle.

The fields found in the statues, however, are far stronger — in some cases nearly four times that of the Earth’s magnetic field.