Final answer:
Humans do not usually have a strong resistance to emerging diseases and can be susceptible to them, especially when pathogens evolve and develop resistance to treatments such as antibiotics.
Step-by-step explanation:
The statement that humans usually have developed strong resistance to emerging diseases is false. While humans possess a highly adaptable immune system, resistance to new diseases often requires exposure and time for the population to develop immunity, either through natural processes or vaccination. Additionally, various factors can impede the development of immunity.
For instance, the excessive use of antibiotics has resulted in the natural selection of resistant forms of bacteria. Contrary to the immunity a person might acquire after recovering from certain infections, these bacteria do not provide immunity but instead become tougher to eradicate, posing a serious health threat.
Generally, human populations are not immune to common colds because the viruses that cause them, such as rhinoviruses, have many different strains and can mutate, allowing them to bypass previous immune responses. Continuous evolution, typified by the adaptation of viruses and bacteria to medications such as antibiotics, makes it difficult for humans to maintain strong resistance to all emerging diseases.
Historical examples include diseases that became dormant and returned more virulently, such as the bubonic plague, or those like tuberculosis, which never disappeared but re-emerged, especially in areas with populations compromised by other health issues. Despite previous natural immunities, some diseases can adapt rapidly to overcome them, as happened between the fourteenth and nineteenth centuries with certain bacilli.