The earliest known bed bug fossils date to 1352 B.C. and were discovered at an Egyptian archeological site, according to the book "Bed Bug: The Return of the World's Most Reviled Household Pest." The parasitic insects likely existed before then, however, and opportunistically infested humans and bats in caves.
Bed bugs have evolved to prey upon us, so they are here because we are here too. Like any species low on the food chain, bed bugs can nourish other organisms, such as centipedes. Animals like birds and toads, in turn, eat centipedes. Parasites can also get parasites, such as parasitic bacteria, which would bite the dust if their host went extinct.