The boy's skeleton, according to an international team of researchers, bears all the hallmarks of a hybrid child resulting from the interbreeding of Neanderthals with our direct and most immediate ancestors - so-called anatomically modern humans. If this is true, it means that Neanderthals were not an evolutionary "cul-de-sac" who became extinct. It would also mean that there is a little bit of Neanderthal man, and woman, in all of us.
Excavations around the site at Lagar Velho in central Portugal revealed the signs of a ceremonial burial typical of this period in pre-history. The soil around the boy's bones was heavily stained with red ochre, indicating that the body had been wrapped in some sort of coloured shroud, and his shallow grave was lined with ceremonial stones and the bones of animals such as red deer and rabbit. The archaeologists found a pierced shell of a snail next to the boy's neck, evidently an ornament in a necklace.
Paul Pettitt, a member of the research team and an expert in radiocarbon dating at Oxford University, says that similar burial sites of the Upper Palaeolithic period in Europe demonstrate the rich mortuary rights afforded to high-ranking members of society. "They may have been shamans, sorcerers or other high-status clan members, or, in the Portuguese case, the children of such people," Dr Pettitt says.
But it was the physical nature of the child's bones that have made the Lagar Velho case so unusual and controversial. Professor Erik Trinkaus, an anthropologist from the University of Washington at St Louis and another member of the team, came to the conclusion that the size and proportion of the bones could be explained only by the fact that the boy was a hybridised mixture of Neanderthals and the anatomically modern Homo sapiens - sometimes known as Cro-Magnon Man - a later arrival to Europe who had migrated there from the Middle East.
Anthropologists agree that Cro-Magnons eventually replaced Neanderthals, with the final Neanderthals disappearing from the Iberian peninsula about 30,000 years ago. There has been intense debate about how this came about, with some experts believing that Cro-Magnons committed a form of slow "ethnic cleansing", and others believing that they peacefully usurped the Neanderthals through competition for limited resources. But Trinkaus has another explanation: "Now it seems that when the immigrants met the locals, they made whoopee, not war."
Pettitt points out that the Lagar Velho boy died about 5,000 years after Neanderthals appear to have become extinct on the Iberian peninsula. If the child really does possess Neanderthal traits, then this was no one-off "love child" but the product of continuous interbreeding over several thousand years between Iberian Neanderthals and the early anatomically modern humans who first colonised this region.
Sweeping across western Europe, Cro-Magnon man finally entered the Iberian peninsula but came to a halt at the Ebro frontier, formed by the Ebro river and its tributaries in northern Spain. Anthropologists believe that this prevented the anatomically modern humans from immediately threatening the Neanderthals in what became their final enclave. Pettitt says that for up to 10,000 years there may have been two distinct human species living on either side of the Ebro river. It was only when the modern human beings crossed into the south that their contact with the archaic Neanderthals turned romantic.
"The Lagar Velho child resolves the issue, in that he constitutes smoking- gun evidence of significant contact, at least on the Iberian peninsula. Presumably many opportunities for social and sexual intercourse between the two species existed along the Ebro frontier and the river valleys of northern Spain. The Lagar Velho child demonstrates that a simple model of absolute replacement of archaic humans by moderns with little or no interaction - a `blitzkrieg' - does not hold for this region," Pettitt says.
Ever since the first Neanderthal skull was found in a lime quarry in the Neander Valley in Germany in 1856, scientists have debated the position of this group of early people in the human family tree. Only last year, a DNA analysis of the original Neander Valley skulls found that their owners were too distantly related to have been members of the Homo sapiens species. Pettitt accepts that interbreeding may not have occurred in other parts of Europe, but believes that it did happen on the Iberian peninsula.
Neanderthals first appeared in Europe and the Middle East more than 200,000 years ago. They were short and stocky, compared to the tall and lightly built humans who replaced them. They also had heavy brow ridges and lacked the prominent chins of Homo sapiens. Neanderthal tool culture was more primitive, without the "organic" tools made from bones, ivory and antlers of later humans. These findings have led to the general impression that Neanderthals were somewhat intellectually challenged.
The short arms and legs of Neanderthals, and the thick-set body, are believed to be an adaptation to the cold climate of Ice Age Europe, whereas the tall, long-limbed proportions of Cro-Magnons indicates the African origin of anatomically modern humans. The Lagar Velho boy is a melange of the two body types. The curvature of his long bones, tooth size and proportions, and prominent chin, align him with Homo sapiens. Other features, such as short arms and legs, muscular insertions and thick long bones, connect him with Neanderthals.
Neanderthals and Homo sapiens are formally described as two distinct species, but the appearance of a child at that time in pre-history with such a pronounced mixture of features has thrown a spanner in the works of this idea. So much so, in fact, that some scientists have cast doubt on the hypothesis. Ian Tattersall, of the American Museum of Natural History in Washington DC, and Jeffrey Schwartz, of the University of Pittsburgh, say in a commentary published in the Proceedings of the National Academy of Sciences that the time at which Lagar Velho boy lived, about 5,000 years after Neanderthals had disappeared, precludes a one-off hybrid between two distinct species. "By anyone's reckoning, long-term hybridisation of this kind would indicate that the two populations belonged to the same species. So if [Trinkaus and others] are right, the case is closed: Neanderthals were indeed no more than an odd form of Homo sapiens."
The problem, as Tattersall and Schwartz see it, is that the case is far from closed. Previous claims for "transitions" between Neanderthals and modern humans have not stood up to detailed analysis, and they believe the same will prove to be the case with Lagar Velho boy. They contend that the skeleton lacks any characteristics derived from Neanderthals, and the body was merely a "chunky child" who was a descendent of the modern invaders who had evicted the Neanderthals from Iberia several thousands of years earlier. They say the "brave and imaginative interpretation" of Trinkaus and Zilhao amounts to "courageous speculations".
The Portuguese-led team, meanwhile, has issued a retort claiming that Tattersall and Schwartz are guilty of an "abysmal piece of scholarship", having made several mistakes in their critical analysis of the Portuguese study. The boy who was buried in a shallow grave with a Stone Age ritual ceremony has unwittingly sparked a furious row in his large-brained, long-limbed descendants, more than 25,000 years after his death.