Traces of the skills these men brought with them remain, boosted by a period in the late 1980s when, under perestroika, ten Kazakhs were selected for training at the All Union State Institute of Cinematography in Moscow.
"Those episodes proved to be the single most important stimulus for the major transformations in human history, " said Weiss, who digs through the traces of vanished empires for evidence of these climatic events.
Humans are not adapted to these natural chemicals, in which the margin of safety is about tenfold compared with traces in synthetic pesticides (some 10, 000-fold higher).