Final answer:
Viruses can emerge and spread by acquiring changes in their genetic material, allowing them to bind to receptors in new hosts. They infect and multiply by using the host cell's replication processes and burst out of the host cell in a lysis process. The origin of viruses is still unknown, but they likely evolved by acquiring genetic material over time.
Step-by-step explanation:
Viruses can emerge and spread by undergoing changes in their genetic material that allow them to bind to receptors in new hosts. This happens randomly and frequently during viral reproduction. Once a virus with new binding properties comes into contact with a suitable host, it can spread quickly. New viruses infect and multiply by attaching to receptors on host cell surfaces, penetrating the cell membrane or wall, injecting their genetic material into the host cell, and using the host cell's replication processes to produce copies of the viral DNA and proteins. Eventually, the new viruses assemble using the viral DNA and host cell-produced protein coat, and then burst out of the host cell in a lysis process. Viruses have likely emerged and evolved over time by acquiring bits of genetic material from various sources, and they depend on their host cells to replicate and grow. Since they do not fossilize, the exact origin of viruses is still unknown, and scientists study their evolutionary history by examining how present-day viruses evolve and using genetic and biochemical information.