Ancient DNA of Humans and Their Pathogens
Advances in method of ancient DNA analysis over the past ten years have transformed our views of human interactions and migrations as well as of the evolutionary dynamics of several of our pathogens. We now know that admixture among archaic and modern humans was common and that human populations have been quite dynamic, both in terms of migrations and admixture and in terms of rapid allele changes that enable environmental adaptation. Questions that remain include what was the role of selection after admixture between archaic and modern humans, how has climate change affected human diversity in the past, can we understand selective pressures on complex traits over time, and what was the diversity and structure of ancient African populations? Ancient DNA has also presented surprises about the emergence of some human pathogens; for example, Y. pestis, the causative agent of plague, has affected humans for much longer than expected, while M. tuberculosis, causing TB, appears to have jumped into humans more recently than previously thought. What may be impossible to know are how these population dynamics (for both humans and pathogens) played out in environments, such as the tropics, where DNA preservation is poor. In addition, some pathogens, such as single stranded RNA viruses may not preserve in any (or most) environments because of their rapid degradation after death. Insights from other ancient biomolecules, including proteins, and additional methodological improvements may overcome some of these obstacles.