Final answer:
Influenza viruses have the ability to evolve and can undergo genetic changes through antigenic shift. Pigs can act as a vector or intermediate host for the swine flu, also known as H1N1.
Step-by-step explanation:
Influenza viruses, including the flu virus, have the ability to evolve and adapt over time. They can undergo genetic changes through two mechanisms: antigen drift and antigenic shift. Antigenic shift occurs when a virus with new binding properties comes into contact with a suitable host, leading to a potential new strain of the virus. In the case of the swine flu, also known as H1N1, pigs can be a vector or intermediate host for the virus and play a role in its evolution and transmission.