Final answer:
Human tapeworms are part of the cestode family of parasites with complex life cycles, often requiring multiple hosts, and are specifically adapted to their primary hosts, one of which is humans through consumption of contaminated meat.
Step-by-step explanation:
The ancestry of human tapeworms can be traced back through their complex reproductive cycles and host-specific relationships. Tapeworms are types of flatworms known as cestodes and are often host-specific, showing a high level of adaptation through evolution. For example, Taenia saginata can only infect humans. These parasites have intricate life cycles, frequently involving multiple hosts, to facilitate their reproduction and survival. Humans can become hosts to adult tapeworms by consuming contaminated and undercooked meat, such as pork, beef, or fish, leading to diseases. Tapeworms attach to the intestine wall of their primary host with hooks and absorb nutrients directly from the host's food, lacking their own digestive systems. Their body is made up of segments called proglottids, which after fertilization, release eggs that can be consumed by an intermediate host, completing their life cycle.