Final answer:
It is true that both infectious and chronic diseases influence human mortality rates and can act as selective agents in natural selection by affecting survival and reproduction.
Step-by-step explanation:
It is true that both infectious diseases and chronic diseases can influence mortality rates in humans and act as selective agents under natural selection. Infectious diseases, such as pertussis, influenza, and tuberculosis, can spread through populations, affecting individuals' chances of survival and reproduction, which are central to the process of natural selection. On the other hand, chronic diseases such as heart disease, stroke, and cancer generally affect individuals over a longer period and have a higher prevalence in older adults. Both types of diseases can shape population genetics by affecting individuals' overall fitness in a given environment. For example, individuals with genetic resistance to certain infectious diseases may be more likely to survive and pass on their genes, while those with genetic predispositions to chronic diseases may have a different reproductive outcome.