In this argument, the author concludes that humans were not a factor in the extinction of large mammal species found in the Kaliko islands 7,000 years ago. The author has tried to justify his statements by pointing out that there is no evidence that the humans had any significant contact with the mammals. According to him, while archeologists have found bones of discarded fish in the islands, they have not found any discarded mammal bones there. However, the author has not considered the possibility that humans might have exported the parts of mammals especially bones during that period. The author has completely overlooked this possibility. Without considering this explanation, he has jumped to the conclusion that humans were not a factor in their extinction from the islands. There is also a possibility that the humans hunted the large mammals for food, and disposed the bones as well so that none was left behind as evidence. There are many cultures that destroy the bones and all other parts of mammals. Hence, this could be a reason that there was simply nothing left of the mammals to be found by the archaeologists. Hence, this point taken by the author is not valid.
This argument depends upon the author's assumption that without significant contact with these mammal species, humans could not have been a factor in their extinction. It might be that the humans had not done anything significant to these animals, but intruded their territory and natural habitat. As a result, these animals might have left their living areas. There is also a possibility of the humans destroying the food sources of the mammal species knowingly or unknowingly. Perhaps the humans consumed the plants and animals on which these species relied for their existence. These days many species are facing extinction due not to the animals being killed by humans, but by the elimination of their food sources and habitats. The humans are encroaching upon their living spaces to accommodate their increasing population. The author has failed to address these possibilities. Hence, it critically weakens the argument.
Lastly, the author has assumed that the bones of fish that archeologists have found discarded on the island were discarded by human beings, and not by some other large animal. However, the speaker has provided no evidence to support this assumption. The same thing applies to the mammals also. Hence, this evidence lends little credibility to the author's theory about the extinction of large species of mammals.
The evidence given by the author in his support is very unconvincing. To strengthen his argument, the speaker should have ruled out the possibility that humans exported the bones of these other species or that some other animal has not eaten these species. The author must have collected information about the food habits of the humans and these mammal species during that time. That would have helped to evaluate the actual reason for the extinction of these species. Without the right information, this argument is pure speculation and cannot be justified.