Wikipedia says there are more than a hundred billion wild mammals. [1] They obviously do not all consume as much food as humans do and there are certainly a lot

Wikipedia says there are more than a hundred billion wild mammals. [1] They obviously do not all consume as much food as humans do and there are certainly a lot of small mammals like mice, but from the order of magnitude it seems at least not completely obvious that ten billion people would be too much to support without fertilizers other than dung and similar things. From a different angle, Wikipedia says there are about 1.4 billion hectares of arable land and the best number I could quickly find is that one needs one to two hectares per person without modern fertilizers, that would imply a limit of only about a billion people. [1] https://en.wikipedia.org/wiki/Lists_of_mammals_by_population https://en.wikipedia.org/wiki/Lists_of_mammals_by_population [2] https://en.wikipedia.org/wiki/Arable_land https://en.wikipedia.org/wiki/Arable_land