Early humans from Java used shells for tools and engraving long before Homo sapiens did, new research suggests.
The findings, published today in the journal Nature suggest the ability to carry out deliberate engravings was present in human ancestors previously thought to be incapable of such things.
"The only conclusion you can come to is that Homo erectusengraved these markings," says co-author Dr Stephen Munro, a palaeoanthropologist with the Australian National University and a curator at the National Museum of Australia.
"I guess this brings them a little bit closer to us because we can identify with deliberately-made markings."
Munro and colleagues analysed fossilised freshwater mussel shells that were first discovered in the 1890s, alongside Homo erectus bones found at Trinil in Java.
"They have been buried for half a million years," says Munro.
Munro says the shells seemed to have been deliberately collected as they were all the same large size.
"They fit nicely in the palm of your hand."
In 2007, as part of his PhD, Munro took digital photographs of the shells and examined them closely on computer. It was then that he found one of them had a geometrical pattern engraved on it.
"I was completely flabbergasted," he says, "this type of engraving in the archaeological record doesn't show up anywhere else in the world until about 130,000 years ago."
Munro says the team went through an exhaustive process to eliminate all the other possible explanations for the engravings.
"Nobody has come up with another explanation," he says.
The research team used microscopic analysis to confirm the engravings were as old as the shell.
Munro says the engravings may have not been discovered before because they are difficult to see with the naked eye and only stand out on the fossils in the digital photographs.
"When these bivalves were alive they would have had a dark covering of organic material. When you engraved into that you would have engraved through the organic matter and got into the white and so it would have been quite striking."
However, it's too early to say what the engravings mean.
"Was it just a doodle? Answering this is beyond the scope of this study," says Munro.
"Maybe if we start discovering more of these things, we can start to explore the function of such markings.
The researchers also found that one of the shells had clear evidence of being turned into a tool.
"It had a deliberately-made sharp cutting edge," says Munro.
Other shells showed fracture patterns, notches and holes that also suggested they had been opened, says Munro.
Although early humans are known to have used tools, this is the first time shell tools have been found alongsideHomo erectus bones.
The discovery of engravings on shells fits with a hypothesis that Munro favours, which is that early humans evolved by the sea and ate shellfish rather than chased antelopes on open savannas.
To date there has been no evidence that early humans ate shellfish but Munro thinks this is partly because of a bias in research towards the savanna hypothesis, and a belief that early humans ate meat instead of shellfish.
"There's a wealth of other fauna information at many sites, including fish and shellfish," says Munro.
"But these are often just left in the ground and not collected and taken back to a museum."
It is often hard to tell from shellfish remains themselves, whether they have been manipulated by humans.
But the latest findings, says Munro, changes that story.
"It's impossible to believe that an animal such as Homo erectus would have been using the shells as tools, that they were engraving the shells, that they were collecting and opening shells but not eating the shellfish."
Munro says the idea that humans evolved eating shellfish on the coast is supported by a number of other facts.
For example, he points out, humans are slow and they don't climb.
And they lost their fur and developed a layer of fat, which together with a linear body shape suits a water environment.
The omega-3 fatty acids in a shellfish diet could also have played an important role in the development of humans' big brains, Munro suggests.
And last but not least, learning how to hold the breath to dive for shellfish in shallow waters, would have led to one of the pre-requisites for human speech, says Munro.
I saw this this week and it is very interesting news. It shows a lot of our ideas about the Cro Magnon and art are not completely correct.