Final answer:
The statement relates to the trade-off theory of virulence in pathogens, emphasizing the balance pathogens must strike between harming their host and ensuring their own transmission and survival through the process of natural selection.
Step-by-step explanation:
The statement "Natural selection should favor pathogens that strike an optimal balance between the costs and benefits of harming their hosts" describes the trade-off theory of virulence in pathogens. This principle outlines that while pathogens, which include viruses and bacteria, need to exploit their hosts to replicate and transmit to new individuals, causing too much harm can be counterproductive. If a pathogen is too lethal, it risks killing its host before it can spread, while if it's not harmful enough, it might be outcompeted by other pathogens.
Hence, evolution through natural selection often leads to a balance where the pathogen is harmful enough to ensure its spread and replication but not so harmful as to drastically reduce its chances of transmission. Understanding this balance is pivotal as it impacts the development of diseases within populations and guides the evolution of both pathogens and host defense mechanisms.