Justin E. H. Smith in the Chronicle of Higher Education:
The hard data tell us that what is happening to animals right now is part of the same broad historical process that has swept up humans: We are all being homogenized, subjected to uniform standards, domesticated. A curiosity that might help to drive this home: At present, the total biomass of mammals raised for food vastly exceeds the biomass of all mammalian wildlife on the planet (it also exceeds that of the human species itself). This was certainly not the case 10,000 or so years ago, at the dawn of the age of pastoralism.
It is hard to know where exactly, or even inexactly, to place the boundary between prehistory and history. Indeed, some authors argue that the very idea of prehistory is a sort of artificial buffer zone set up to protect properly human society from the vast expanse of mere nature that preceded us. But if we must set up a boundary, I suggest the moment when human beings began to dominate and control other large mammals for their own, human ends.
More here.