However, there simply does not seem to be sufficient evidence for the disease hypothesis. First, there has been no evidence of disease found. Next, even extremely virulent diseases, like the plague or West Nile Virus, do not have the kill rates necessary to cause the extinction of an entire species. In addition, one has to realize that the extinction of large mammals coincided with the extinction of other animals, like birds, marsupials, placentals, testudines, and crocodilians. It is unlikely that a disease would be lethal in such a wide-variety of animal populations, especially when it did not destroy all species of certain animal genus. The final theory is that a meteor killed the large mammals. There is evidence that meteor impacts caused earlier extinctions like the Permian-Triassic extinction and the extinction of the dinosaurs. Meteor impacts can interfere with food sources, because the resulting dust in the air interferes with photosynthesis. Meteors may also indirectly cause acid rain. In addition, there is the slim possibility that impacts could cause large-scale...

Meteors are strongly linked to the extinction of the dinosaurs, but no evidence of a sufficiently-large meteor supports impact as a cause of the large animal extinction at the end of the last ice age.
Regardless of what actually began the death and dying among the large mammals, it is easy to understand why the animals became extinct. Each species has what mathematical ecologists refer to as an "extinction threshold," and when the numbers of a species dip below that threshold, it becomes easy for the species to become extinct. Lower numbers, caused by one factor, like climate change or disease, would make it easier for an intervening factor, like human predation, to cause the extinction of a species. Furthermore, smaller numbers means less genetic adversity, which could result in death over a relatively short period of time. Large mammals, with their smaller populations and longer lifespans, and longer gestation periods would be more susceptible to any of the possible causes of extinction than smaller mammals.