Religious studies lecturer David G. Robertson writes that Icke's reptilian idea is adapted from Zecharia Sitchin's "The 12th Planet" (1976), combined with material from Credo Mutwa, a Zulu healer. Sitchin suggested that the Anunnaki came to Earth for its precious metals. Icke has said that they came for what he refers to as "mono-atomic gold", which he claims can increase the capacity of the nervous system ten-thousand fold, and that after ingesting it the Anunnaki can process vast amounts of information, speed up trans-dimensional travel, and shapeshift from reptilian to human. Lewis and Kahn argue that Icke is using allegory to depict the alien, and alienating, nature of global capitalism. Icke has said he is not using allegory.