Image caption Maize played a central role in the establishment of early Andean civilisations, say researchers

New evidence strengthens the argument that maize played an important role in ancient Peruvian civilisation 5,000 years ago, a study has said.

Samples taken from pollen records, stone tool residues and fossilised faeces suggest the food crop was actively grown, processed and eaten.

The authors say it adds more weight to the argument that Andean society was agricultural, not maritime-based.

The findings appear in the Proceedings of the National Academy of Sciences.

"If you look at the origins of civilisations around the world - from Egypt to China and India - they are all based on agriculture," explained co-author Jonathan Haas from The Field Museum, Chicago.

However, he told BBC News that an idea emerged that Andean early civilisation was different, and evolved from exploiting marine resources.

Power struggle

He told BBC News: "That theory has now been the dominant theory since the mid-1970s but more data has become available saying that there are not just [coastal] sites but there are some big inland sites too.

"People started to find corn at the inland sites, and the argument was that the corn was really a condiment and used for ceremonial purposes.

Image caption An agricultural system would allow leaders to exert the power needed to develop complex societies

Dr Haas said that the findings from the team's study "topples that notion".

In their paper, the team explained that the first stage of identifying the botanical remains taken from the archaeological sites was the analysis of the macrobotanical (visible to the naked eye) artefacts.

"Analyses of hundreds of samples… revealed that macroscopic remains of maize - including kernels, leaves, stalks and cobs - were rare," they wrote.

They added that the reason for the lack of such samples at the sites has "yet to be resolved", but the lack of such remains could not be seen as evidence of the absence of maize.

"It is also possible that the lack of macroscopic remains is a reflection of limited excavations at these sites, given that the more extensive excavation of sites… did yield much more macroscopic evidence of maize."

Microscopic bounty

The team commented that the scarcity of macroscopic remains was in marked contrast to an abundance of microscopic evidence of maize in the guise of maize pollen samples collected from soil at the sites.

Although there was a possibility of contamination from modern sources, the team said that there were three factors that weighed against this.

"First, modern maize pollen grains are larger and turn red when stain is applied, whereas ancient grains do not," they said.

"Second, extraction of pollen samples followed standard archaeological guidelines and all crew members were trained in taking pollen samples.

"Third, the modern samples all contained pollen from a plant not found in the area prehistorically."

Dr Haas said that the pollen record gathered from the study sites was unequalled, with the data being accessed by other scientists in their research projects.

Other artefacts the team examined included 14 stone tools, which were radiocarbon-dated to between 2090 and 2540BC.

"Eleven of the 14 tools had predominantly or exclusively maize starch grains on the working surfaces, and two working surfaces had maize phytoliths (mineral excretions by the plant)," they recorded.

The researchers also found samples of sweet potato and bean starch grains.

The team also recovered 62 coprolites (fossilised faeces), of which 34 were human specimens.

They wrote that 69% of the specimens contained maize starch grains, the dominant source of starch in the diet at that time.

Dr Haas observed: "Maritime resources were important as it was their primary source of protein. But in each one of those coprolites, there was, on average, half an anchovy - that is not your diet, that is a condiment.

"In contrast, finding corn, beans, sweet potato and a number of other things in the diet - that is an agriculturally-based society."

He added that a vibrant agriculture system would result in a surplus of food, allowing the societal leaders to attract outsiders to the area and exert power.

The team wrote: "It was during this time that large permanent communities were settled, monumental architecture first appeared on the landscape, agriculture was more fully developed and indicators of a distinctive Andean religion are manifest in the archaeological record."