An interesting claim that made the news a few days ago

Roman Empire 'raised HIV threat'

French scientists argue that people who lack a particular gene (CCR5-Delta32) seem to be more vulnerable to HIV, and that this is found particularly among those areas that were part of the Roman Empire. It's not because of interbreeding, but rather the result of a disease spread to the areas affected by the Romans. Others argue that other diseases were responsible for the vulnerability, such as bubonic plague.