Iodine deficient?

Neandertal’s prehistoric diet may have lacked a crucial element, says ORNL researcher

Neandertal’s brutish brow and other features are identical to an iodine-deficient human condition called cretinism.
One of the most mysterious creatures that ever walked the earth was Neandertal, a prehistoric human-like being who first appeared about 230,000 years ago in Europe. Scientists have been debating since the first remains were found in 1856: Was he one of us or a separate species?

Neandertal, who looked very human but was burly and stocky, developed a far less sophisticated culture than Cro-Magnon, the first modern humans in Europe, who emerged about 40,000 years ago. Cro-Magnon apparently existed alongside Neandertal, but no one knows whether they made contact or not, either culturally or sexually. After a 200,000-year run, Neandertal vanished.

No one can say for sure what distinguished Neandertals from modern humans, but Computational Physics and Engineering Division researcher Jerry Dobson has a theory. In an article soon to be published in the Geographical Review, he suggests that Neandertals may have been iodine deficient. A single genetic difference in the thyroid gland, which controls iodine extraction from food, could account for many other differences in bone structure and body shape.

The bones of Neandertal (the spelling scholars prefer over Neanderthal) were first unearthed in Germany but since have been found in inland areas throughout Europe and Western Asia. They reveal numerous similarities to modern humans who suffer from iodine deficiency disorder—in its most severe form, cretinism.

“Distinctive Neandertal traits—overall body proportions, heavy brows and muscles, dental development and wear and propensities for degenerative joint diseases—are identical to those of modern humans suffering from cretinism,” Dobson says. “Whether it was biological—a genetically restricted ability to process iodine—or pathological—a dietary deficiency—I can’t say.

“Neandertals lived in areas away from the coast that are iodine deficient even today. If you and I took up residence in those same sites without a supplemental source of iodine, we’d suffer from iodine deficiency. Our children would suffer even more, and our grandchildren would be physically deformed and mentally retarded, as many Alpine Europeans were in the late 1800s. I suspect Neandertals were even more susceptible than we are.”

Some 30 percent of the world’s current population is at risk from iodine deficiency disorder, and 750 million suffer from goiter, which is caused by lack of iodine in the diet.

“I’ve concluded that a single factor, iodine, can account for most differences between modern humans and Neandertal, and the mechanism of change may have been a single genetic modification that improved the efficiency of modern thyroid glands to extract iodine,” he says.

So how did Dobson, a geographer who specializes in geographic information systems, get onto Neandertal’s case?

“I started with geographic questions about sea-level rises associated with global warming. Typical projections run from a few centimeters to a meter or more, but geologists have firmly established that sea level has risen 125 meters since the last ice age,” Dobson says.

“I asked myself: If the ice age coast of 18,000 years ago is missing, what does that imply about the archaeological record? Is what archaeologists find on dry land today identical to what existed in coastal lowlands, now tens of meters beneath the sea? Is there, perhaps, some factor that would cause a systematic difference between coastal and interior populations?

“It was my brother, Jeff, who suggested iodine as a distinguishing factor between coastal and inland populations. Iodine comes almost entirely from three sources—saltwater fish, shellfish and seaweed—all coastal. People who didn’t know to take iodine with them when they moved inland would suffer goiter and cretinism. Jeff also learned that, even today, the most iodine-poor regions on earth are those that are mountainous or formerly glaciated. That, in turn, led me to ask, ‘Neandertals lived in mountainous, glaciated Europe. How did they get iodine?’ I compared the bones of Neandertals to the bones of modern-day cretins and found they matched.

“Most investigation of the ice ages focuses on glaciers. But what about tropical lowlands? During the ice ages, those would have been the most hospitable habitats on earth. As the glaciers retreated, sea level rose, inundating those habitats and forcing people inland. That would create tremendous population pressure and force coastal people to compete for resources. Those who moved inland would have suffered a terrible fate without sufficient iodine. Most Neandertal fossils correspond with periods when sea level was high, so they may have been refugees from that coastal competition.”

Much of the archaeological evidence of early humans probably lies undersea. Even today, Dobson points out, most people live near the sea, which provides ample iodine in the diet. If Neandertal did suffer an iodine deficiency, either through a dietary dearth or physiological inability to extract it, it would have spread through generations because iodine is very important to fetal development. Babies, although apparently normal at birth, soon develop the large head and bones, curved spine, mental and physical retardation, achy joints and other infirmities we know as cretinism.

Cro-Magnon, living in those same sites, may have been equipped with a more efficient thyroid gland and undoubtedly obtained iodine from some additional source, perhaps by trading with the iodine-rich coast. They were able to outcompete Neandertal and prosper, but they, too, suffered from cretinism.

Their sites contain carved squat “Venus” figurines that look precisely like mature women cretins. They apparently worshiped that particular form, Dobson says, but it’s impossible to say whether they knew those figurines looked like Neandertals.

In his November 1998 column in GeoWorld magazine, Dobson called for better data on iodine’s global distribution that could be achieved by geographic information system techniques.

The iodine theory evolved out of an Laboratory Directed R&D-funded project to explore the coastal-change aspects of global warming since the ice ages. The Geographical Review article has attracted a number of media requests.—B.C.