Foster: Many species of extremely large North American mammals became extinct during the last ice age, which was also the time of the first human migration to North America. These species could not survive the dramatic changes wrought by this human migration. Fisch: Those extinctions were caused by the dramatic shift to a harsher climate. The climate changed so rapidly that the species could not adapt.
The statement 'Similar species living in parts of the world where there were dramatic changes in climate did not become extinct' most strengthens Fisch's argument.