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A bone from a raven鈥檚 wing with seven regularly spaced notches carved into it is the strongest evidence yet that Neanderthals had an eye for aesthetics.

Evidence that Neanderthals used pigments, buried objects alongside their dead, and collected bird feathers and claws had been taken as signs of behaviours that were once considered unique to our species of Homo sapiens.

But interpreting the motives of ancient humans based on their relics is fraught with difficulty. Incisions in bones and stone objects could be the result of butchery or other practical activities, rather than artistic engravings.

鈥淚t has been proposed that talons and big feathers were used as personal ornaments, but in reality we don鈥檛 have any direct evidence that this was the case,鈥� says Francesco d鈥橢rrico of the University of Bordeaux, France.

So, d鈥橢rrico and colleagues looked for a new approach to interpret a raven bone aged 38,000 to 43,000 years old, found at a Neanderthal site in the Crimea.

Five of the seven notches carved into it are parallel, with a similar depth and shape, suggesting they were cut with the same tool. But notches 2 and 6 look different: they are shallower and angled slightly obliquely.

D鈥橢rrico thinks these two notches were most likely added later to fill in gaps in the original sequence and create a more regular pattern.

鈥淭he interest of these little fragments is that these notches cannot be interpreted as cut marks during butchery,鈥� he says. 鈥淭hey鈥檝e been made by to-and-fro movements; they are too deep and too regular just to be cut marks.鈥�

One possibility is that the notches were to make the object easier to grip: some bone tools appear to have been modified for this purpose.

But the even spacing suggests aesthetic reasons. 鈥淲e tried to find a way to assess how regular they were and whether a Neanderthal could look at them as a regular pattern,鈥� says d鈥橢rrico.

First, the team considered a concept from evolutionary psychology, the Weber fraction. Studies show that there is a limit to our ability to perceive small differences, such as the spaces between lines. If the variation is less than 3 per cent, we tend to think the lines are equidistant.

Using this principle, d鈥橢rrico argues that notches 2 and 6 are needed for the sequence to be perceived as evenly spaced.

To look for more evidence, the researchers asked volunteers to carve evenly spaced notches on turkey bones using stone tools like those the Neanderthals had. The patterns they created were very similar with equidistant spacing. 鈥淲hen you compare it with modern human variability in producing the same type of notch on a bird bone, you see that there was a will by the Neanderthal to make them equidistant,鈥� says d鈥橢rrico.

He thinks it鈥檚 possible that the pattern was symbolic, perhaps as a mark of ownership, but such explanations remain speculative. 鈥淪ome meaning could be attached to it, but of course we don鈥檛 know whether this was symbolic,鈥� he says. 鈥淎t least it was aesthetic, otherwise they wouldn鈥檛 have done it that way, putting such attention to make the notches so regularly spaced.鈥�

D鈥橢rrico says that the approach used in this study 鈥� comparing the artefact with what modern humans can produce 鈥� should be used more in archaeology.

of the University of Barcelona, Spain, agrees, and says he鈥檚 convinced by d鈥橢rrico鈥檚 argument. He even goes further. 鈥淚 can think of no explanation for the pattern of marks other than that it is somehow 鈥榮ymbolic鈥�,鈥� he says.

鈥淚t鈥檚 very interesting, although it remains to be seen whether this will develop into a pattern of observations from Neanderthal sites,鈥� says of Bournemouth University, UK. 鈥淲e shouldn鈥檛 be that surprised to see evidence that our closest relatives share behavioural traits with us, including activities that don鈥檛 only have a utilitarian use.鈥�

of the Natural History Museum, London, says it鈥檚 significant to see this style of engraving associated with Neanderthals. 鈥淭his paper greatly adds to the debate on the cognitive abilities of Neanderthals and further reduces the assumed differences between Neanderthal and modern human behaviour,鈥� she says.