Two contrasting ideas, that humans are ‘part of the ecosystem’ (i.e. a constitutive element of the ecosystems they exploit) and that humans are ‘a cancer on the Earth’, are examined in the light of the current despoliation of the biosphere. It is concluded that neither can describe our longer-term ecological role on Earth, which, at best, will have to resemble that of a co-evolved parasite of the earth’s systems.