Modern human DNA is everywhere: on the hands of excavators, in the air of museum storage rooms, in the equipment used in the laboratory.

Ancient DNA degrades into short fragments over thousands of years, making it increasingly difficult to distinguish from the intact modern DNA that contaminates everything it touches.

Without stringent protocols to prevent contamination and sophisticated methods to detect and exclude it, the results of ancient DNA analysis from Egypt could not be trusted.

The other fundamental obstacle is the climate.

DNA degrades faster in warm conditions.

The warm, humid environment of many Egyptian burial sites — even desert sites that might appear to be ideal for preservation — accelerates the biochemical processes that break DNA apart.