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The partially pieced together skull of an early human has a brain capacity at the larger end of modern standards, yet dates from 200,000-160,000 years ago. The discovery indicates large brains appeared earlier than previously recognized, although what that means for intelligence remains uncertain. The species of the skull's owner remains uncertain, but it is probable this represents the first Denisovan skull ever found, marking a major step forwards in our understanding of this mysterious population.
Since the 1970s, 21 hominin fossil fragments have been found at a site at Xujiayao, northern China. Based on their ages and the bones found they were judged to come from at least 10 individuals, making it difficult to put together those with a common source.
However, a team led by Dr Xiu-Jie Wu of the Chinese Academy of Sciences has re-examined three pieces of skull from the Xujiayao site and reports in the Journal of Human Evolution that they are almost certainly from the same individual. Although there are pieces missing, the three fragments align perfectly at certain points (as seen above). Wu told IFLScience this was only possible using CT scans that were not available at the time of discovery. Together, they represent most of the rear of a skull, enough to offer a good estimate of the total skull capacity.
It's not possible to perfectly calculate cranial capacity from partial skulls, particularly when dealing with a species we know little about. As the paper notes, “The shape of the modern human cranium is more rounded/ encephalized with different proportions than in other Homo taxa.” Since we don't know what the shape of the front of this individual's skull looked like, there is some inevitable imprecision.
Nevertheless, Wu and co-authors conclude the brain capacity was 1,700 cm3, above average for a person living today. The individual in question is believed to have been an adolescent male, who Wu told IFLScience might have had a little more growing to do, but "Should be very close to an adult."
In the absence of DNA from Xujiayao or matching skull regions from sites, no one can be certain of the skull's species. However, Wu told IFLScience there are two reasons she thinks it came from a Denisovan. Not only do the ages match, but "Both Xujiayao and Xuchang have mosaic features of Neanderthals, Asian archaic and modern humans," just as we would expect for a Denisovan.
Physical evidence of Denisovans is few and far between with just a handful of teeth and bone fragments found in the Denisova Cave in Siberia from where the species gets its name, and a jawbone from high on the Tibetan Plateau. Having part of a skull that indicates brain size furthers our understanding of this mysterious strand of the human family tree.
Over the 2 billion years Australopithecines survived their brain sizes grew slowly, and the trend accelerated with the arrival of the genus Homo. Nevertheless, exceptions have emerged to what once seemed a simple story of steadily increasing skull dimensions. Homo naledi, for example, was originally thought to be much more ancient than its 300,000-400,000 years because their brain sizes fitted an earlier time. Likewise, the relatively recent “hobbits”, Homo floresiensis, were very small-brained by the standards of their day.
The Xujiayao skull appears to be a reverse example; an individual with a brain size more suited to the modern-day than their timeline in the ice age before last. With only a single, incomplete, skull, we can't tell if the individual in question was an outlier, or if he came from a species at least as big-brained as ourselves. The first skulls recognized as Homo Sapiens, dating from more than 300,000 years ago, were considerably smaller at 1,300-1,400 cm3.
Anthropologists are so interested in brain size because, to some extent, it acts as a proxy for intelligence. However, the match is imperfect. Larger bodies need larger brains to do the same work, or blue whales would be orders of magnitude smarter than dolphins. In adapting to cold climates, brains can develop extra insulation that bulks up the skull size without adding any extra intellect. The Denisovans lived in cold environments, and the bones we have from them are hefty, so their skull size may exaggerate their intelligence.
