Carl Zimmer muses on parasitism

Spontaneous generation was the best explanation for parasites, given the evidence at hand. But, it was also a profound heresy. The Bible taught that life was created by God in the first week of creation, and every creature was a reflection of His design and His beneficence. Everything that lived today must descend from those primordial creatures, in an unbroken chain of parents and children -- nothing could later come squirting into existence thanks to some vital, untamed force. If our own blood could spontaneously generate life, what help did it need from God back in the days of Genesis?
The mysterious nature of parasites created a strange, disturbing catechism of its own. Why did God create parasites? To keep us from being too proud, by reminding us that we were merely dust. How did parasites get into us? They must have been put there by God, since there was no apparent way for them to get in by themselves. Perhaps they were passed down through generations within our bodies to the bodies of our children. Did that mean that Adam, who was created in purest innocence, came into being already loaded with parasites? Maybe the parasites were created in him after his fall. But wouldn't this be a second creation, an eighth day added on to the first week. . . Well, then, maybe Adam was created with parasites after all, but in Eden parasites were his helpmates. They ate the food he couldn't fully digest and licked his wounds clean from within. But why should Adam, created not only in innocence but in perfection, need any help at all? Here the catechism seems to have finally fallen apart. Carl Zimmer, Parasite Rex: Inside the Bizarre World of Nature's Most Dangerous Creatures (New York: Free Press, 2000, p. 5)

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