Ata has the bone characteristics of a six- or seven-year-old child.

To study the specimen, Nolan sought clues in Ata's genome. He initially presumed the specimen was tens or hundreds of thousands of years old - the Atacama Desert may be the driest spot on the planet, so Ata could have been preserved for aeons. He consulted experts who had extracted DNA from bones of the Denisovans, an Asian relative of European Stone Age Neandertals. It turned out that their protocols weren't necessary. "The DNA was modern, abundant, and high quality," he says, indicating that the specimen is probably a few decades old.

To the chagrin of UFO hunters, Ata is decidedly of this world. After mapping more than 500 million reads to a reference human genome, equating to 17.7-fold coverage of the genome, Nolan concluded that Ata "is human, there's no doubt about it". Moreover, the specimen's B2 haplotype-a category of mitochondrial DNA - reveals that its mother was from the west coast of South America: Chile, that is.

Meanwhile, after examining X-rays, Lachman concluded that Ata's skeletal development, based on the density of the epiphyseal plates of the knees (growth plates at the end of long bones found only in children), surprisingly appears to be equivalent to that of a six- to eight-year-old child. If that holds up, there are two possibilities, Nolan says. One, a long shot, is that Ata had a severe form of dwarfism, was actually born as a tiny human, and lived until that calendar age. To test that hypothesis, he will try to extract haemoglobin from the specimen's bone marrow and compare the relative amounts of foetal versus adult haemoglobin proteins. The second possibility is that Ata, the size of a 22-week-old foetus, suffered from a severe form of a rare rapid ageing disease, progeria, and died in the womb or after premature birth.

Nolan hasn't yet turned up hits for genes known to be associated with progeria or dwarfism. He's stepping up the search for mutations through additional sequencing and casting a wider net. Another possibility is a teratogen: a birth defect-inducing toxicant along the lines of thalidomide. Nolan plans to analyse tissue using mass spectrometry to look for toxicants or metabolites. But reports of a handful of other Tom Thumb-sized skeletons from Russia and elsewhere have Nolan leaning toward a genetic explanation.