that human hunters would drive a fairly large variety of animals into extinction fairly suddenly,”he argues.Douglas believes the impact may also have resulted in the disappearance of the Clovis culture. Archaeological evidence shows that the Clovis culture was once found across North America,but that it became fragmented about 13,000 years ago,suggesting a catastrophe paralleling the disappearance of the large mammals.Above the aforementioned sediment layer,no Clovis spearheads can be found,and artifacts of post-Clovis cultures show greater diversity from one area of North America to another. Douglas believes that this suggests population fragmentation,in which smaller groups across the continent had little interaction and developed different cultural traditions.