例如，艾伦说：“例如，我们现在了解到，中世纪的天花大流行，而不是瘟疫，而是请您，而是天花，剩下的几代人患有罕见的遗传缺陷，可以保护他们免受艾滋病毒感染的感染，艾滋病毒是引起艾滋病的病毒。我们估计，从北欧人降落的人中，大约有1％对艾滋病毒感染无关。
(For instance," said Alan, "we're now learning that the smallpox pandemics of the Middle Ages, not the plague, mind you, but smallpox, left generations of people with a rare genetic defect that protects them against infection by HIV, the virus that causes AIDS. We estimate that approximately one percent of people descended from northern Europeans are virtually immune to HIV infection.)