Zoologist: Every domesticated large mammal species now in existence was domesticated thousands of years ago. Since those days, people undoubtedly tried innumerable times to domesticate each of the wild large mammal species that seemed worth domesticating. Clearly, ttherefore, most wild large mammal species in existence today either would be difficult to domesticate or would not be worth domesticating. The zoologist's argument requires the assumption that ['not all of the large mammal species that were domesticated in the past are still in existence', 'in spite of the difficulties encountered, at one time or another people have tried to domesticate each wild large mammal species', 'of all the domesticated large mammal species in existence today, the very first to be domesticated were the easiest to domesticate', 'it is not much easier today to domesticate wild large mammal species than it was in the past']