When Europeans first came to North America, one of the most disastrous impacts on native populations was the introduction of "Old World diseases." These diseases, such as smallpox, influenza, and plague, devastated the Native American population as the number of settlers grew steadily. One author has called this "the greatest human catastrophe in history, far exceeding . . . the Black Death of Medieval Europe." Based on this scenario and what you know about the immune system, what can you conclude about the Native American and European populations?