"Since leaves can simply be used to add comfort to sedge bedding we were even more surprised when we discovered that the leaves used have insecticidal properties," said Wadley. She surmised they probably were used to repel mosquitoes from the site, which is near the UThongathi River.
"The use of plants and other biological organisms and substances for medicine and other health-related uses is a fascinating aspect of modern human cultures," said Carolyn Ehardt, program director for biological anthropology at the National Science Foundation, which partially funded the research. "Anthropologists have been studying human ethnomedical and ethnobiological systems extensively, aiding in the discovery of new drugs and other therapies. It is quite interesting to gain this level of historical depth to the apparent recognition by these people of the beneficial properties in the local flora."
Marion Bamford, a botanist with the Bernard Price Institute for Palaeontological Research at Witwatersrand, identified the sedges as belonging to a plant called Cryptocarya woodii, or River Wild-quince. C. woodii contains chemicals that have insecticidal and larvicidal properties.
The chemicals have different effects on different insects. "For some insects there is a 'knock-down' effect," said Wadley. "Others are repelled and the breeding rate is interfered with amongst some insects."
C. woodii is in the same family as the Bay leaf, which has culinary use, but is also suitable for storing in grains to repel insects that would eat them.
The research included examining blocks of sediment from the site that had been undisturbed for thousands of years to determine their contents. Paul Goldberg and Francesco B
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National Science Foundation