The conclusion is that most species are either too difficult to domesticate or are not worth it. We only need one of these things to be true, not both. Even if people have only attempted to domesticate a very small portion of species, the rest could simply not be worth it and our conclusion would be unaffected.

If it’s way easier to domesticate large mammal species than it was 1000 years ago, then it makes no sense to claim that most species are either too hard to domesticate or not worth it. The ones humans failed to domesticate in the past would be easier now, and the conclusion would fall apart.

The conclusion is about species in existence today, so we don’t care about species that went extinct. We are also only concerned with the amount of undomesticated species that are either too difficult or not worth it, not with the amount of domesticated species present today.

(D) is attempting to establish some sort of link between ease of domestication and how worthwhile it is to do so. The presence or absence of this link does not affect the argument, so (D) is not necessary.

If we negate (E)—the first domesticated species weren’t the easiest to domesticate—our argument is unaffected. Perhaps the tenth or twelfth or fiftieth species was the easiest to domesticate, with none of these possibilities affecting the argument.