In a study already drawing the fire of controversy, an American geographer has pointed out evidence suggesting, in his view, that little more than the amount of Iodine in their diets may have been responsible for the physical differences between Neanderthals and modern humans and that this might solve the mystery of what happened to the Neanderthals.
According to this interpretation, the skeletons of Neanderthals bear signs of physical deformities and possibly impaired mental health, which could be a result of iodine-deficient diets. This condition may explain why they were so rapidly and completely replaced by modern humans in Europe about 30,000 years ago. It may even mean that Neanderthals could actually have been anatomically modern humans who were pathologically altered by iodine-deficiency diseases, like cretinism.
Perhaps the Neanderthals did not so much disappear as change their diets some time before 30,000 years ago to include more iodine-rich foods. In that case, this could explain why certain Neanderthal physical traits -- heavy brows, thick bones and musculature and propensities for degenerative joint diseases, which are also associated with iodine-deficiency diseases -- did not persist even if their genes continued into later European populations.
These are the provocative ideas of Dr. Jerome E. Dobson, a geographer at the Oak Ridge National Laboratory, in Tennessee, who crossed into the territory of paleontology and the minefield of Neanderthal studies while examining geographic questions about differences between coastal and inland populations. His analysis is to appear this month in Geographical Review, the journal of the American Geographical Society.
''I compared Neanderthal and cretin morphology and ultimately concluded that Neanderthals were iodine-deficient,'' Dr. Dobson said last week.
Paleontologists who specialize in Neanderthal research have raised sharp objections. Dr. Dobson's conclusions, they contend, are a stretch based on highly circumstantial evidence and at odds with evolutionary biology. But some anthropologists and other geographers said that the data seemed impressive and that the interpretations should be taken seriously.
''We sometimes have to rock the boat,'' said Dr. Karl W. Butzer, a geographer at the University of Texas at Austin. ''Even if this just generates papers that argue against the idea, it will have served a purpose, making the fossil people think and rethink their positions.''
For want of the chemical element iodine, a modern human typically suffers from goiter, an enlargement of the thyroid gland that disfigures the neck, or from cretinism, an even worse condition of physical deformity and mental retardation. Cretinism is caused either by dietary Iodine deficiency or by malfunction or absence of the thyroid gland, which processes Iodine into the thyroid hormone.
Although the addition of iodine to table salt has all but eliminated goiter and cretinism in developed countries, the World Health Organization estimates that 750 million people suffer from goiter and that 5.7 million are cretins. About 30 percent of the world's population is at risk of iodine-deficiency diseases, especially people isolated from the principal sources of dietary iodine like saltwater fish, shellfish and seaweed.
It occurred to Dr. Dobson that Neanderthals mainly lived in such areas in interior Europe during the ice ages. So he set about examining some of the 300 Neanderthal skeletons in museum collections and comparing them with medical descriptions of cretinism and with 17 cretin skeletons at collections in Basel, Switzerland, and Philadelphia.
In both the skeletal examinations and the medical literature, Dr. Dobson was struck by the conspicuous similarities in the overall body proportions, skulls and individual bones of Neanderthals and cretins. Many of the cretins had bulging brow ridges much like those common to Neanderthals. They also seemed to suffer many of the degenerative joint diseases of the jaw, spinal column and hip that afflicted Neanderthals.
''Indeed, Neanderthal skeletons resemble cretins far more closely than they resemble healthy modern humans,'' Dr. Dobson wrote in the journal article. ''Conversely, cretin skeletons resemble Neanderthals more closely than they resemble healthy modern humans.''
The research revealed too many similarities to be coincidental, Dr. Dobson said, and the ''key factor in controlling Neanderthal morphology'' appears to be iodine. This suggested to him that perhaps the critical difference between Neanderthals and modern humans was a single genetic alteration that improved the ability of the modern human thyroid gland to extract and use iodine. This would have given the modern humans who arrived in Europe 40,000 years ago, and are known to Science as the Cro-Magnons, a clear advantage over Neanderthals in a low-iodine environment.
Dr. Dobson even sees hints of Neanderthal cretinism in Cro-Magnon art. He speculated that the ''Venus figurines,'' tiny statues of women with huge breats and bellies and conspicuously exposed genitalia, may not have been fertility symbols, as usually interpreted, but actually representations of the cretinous form the Cro-Magnons remembered from their final encounters with the Neanderthals they replaced.
In any event, Dr. Dobson's thesis has unsettling implications for many issues that have long puzzled scientists since the first Neanderthal skeleton was found in a German quarry in 1856. At first, the skeleton was dismissed as the remains of a Mongolian Cossack who had deserted the Russian Army pursuing Napoleon in 1814. A prominent German scientist examining the bones judged that this had been a modern man who had a bad case of rickets, a calcium deficiency condition.
After the skeleton's greater antiquity was recognized and similar bones were found through Europe, scientists debated the Neanderthals' relationship to modern Homo sapiens. Direct ancestor? Or only an archaic cousin? Tests of mitochondrial DNA, reported earlier this year, suggest that Neanderthals were a separate species that last shared a common ancestor with Homo sapiens no later than 550,000 years ago. But paleontologists specializing in human evolution are not yet sure that the DNA findings can be considered definitive.
As for the fate of the Neanderthals, Dr. Dobson said his analysis could support replacement or continuity.
The prevailing replacement theory holds that all Neanderthals died out and were replaced by modern Homo sapiens, though it has always been puzzling that these hunters who had survived across Europe and western Asia for some 200,000 years should lose out to modern humans, the Cro-Magnons, in the relatively brief time of 10,000 years. Dr. Dobson concluded that iodine deficiency may be the explanation.
The continuity theory posits that some interbreeding occurred between Neanderthals and modern Homo sapiens, meaning that some Neanderthal genes survive in Europeans. Dr. Dobson argued that in genetic terms, Neanderthals may have been anatomically modern humans who were pathologically altered by the effects of iodine deficiency. Through growing trade and other contacts with coastal people, the Neanderthals could have added more iodine to their diets. Superficial differences with modern humans would then have largely disappeared over a few generations, leaving Neanderthals indistinguishable from modern humans in the fossil record.
Dr. Lewis Binford, an anthropologist at Southern Methodist University in Dallas who has studied and written about Neanderthal society, said the new analysis was the first to consider the implications of iodine deficiency in early populations.
''The data seem impressive to me and the hypothesis doesn't seem unreasonable,'' Dr. Binford said. ''We stand to learn something if others investigate the geographic and dietary issues of Neanderthals.''
An authority on Neanderthals, Dr. Fred H. Smith of Northern Illinois University, in De Kalb, said the iodine hypothesis reminded him of the arguments raised, and rejected, in the past to explain away Neanderthal anatomy as examples of rickets-caused deformities.
Dr. Eric Trinkaus, a paleontologist at Washington University, in St. Louis, who has written several books on Neanderthals, also disputed Dr. Dobson's evidence for widespread iodine deficiency in Neanderthal skeletons as well as his interpretations.
''You cannot explain 100,000 to 400,000 years of human evolution based on a pathological condition,'' Dr. Trinkaus said.
Anticipating controversy, Dr. Dobson wrote: ''I might be less bold in offering a new and dramatically different explanation of Neanderthals if prominent experts were satisfied with the debates of the past century or so. But they are not.''