Plant materials (herbs and substances derived from natural sources)[10] were among the treatments for diseases in prehistoric cultures. Since plant materials quickly rot under most conditions, historians are unlikely to fully understand which species were used in prehistoric medicine. A speculative view can be obtained by researching the climate of the respective society and then checking which species continue to grow in similar conditions today[11] and through anthropological studies of existing indigenous peoples.[12][13] Unlike the ancient civilisations which could source plant materials internationally, prehistoric societies would have been restricted to localised areas, though nomadic tribes may have had a greater variety of plant materials at their disposal than more stationary societies.