Waste derived from human activitirs, such as rapeseed placentiform from the extraction of rape oil;fruit faeces from the extraction of fruit juice;chicken excrement from the scall farming of chickens.
Based on an analysis of the faeces of both vegetarians and meat eaters, Dr Hazen suspects bacteria of several genera, including Clostridium and Fusibacterium.
One popular theory is that the wolves which became dogs acted as rubbish-disposal agents for groups of people, by eating their waste, possibly including their faeces.
And further detective work, including examination of the mice's faeces, revealed higher levels of a strain of Clostridium called OUT-1105 in the fat mice than in the thin ones.
Geese and other waterfowl do, nevertheless, seem to form a significant part of polar bears' diets, for studies done in the 1960s found a lot of bird remains in the animals' faeces.