Or any intestinal parasite, come to that? How can there be an intermediary step between being digested and being able to survive and breed in a digestive tract? How did those gross wiggly guys *do* it?
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There is a very simple intermediate between being digested and being able to survive in the gastrointestinal tract: not being digested. Eggs that of a free living planarian which can survive passage through the stomach can produce offsping whose eggs can do the same. The seeds of fruits have also adapted so that they are not digested. The next step is exploiting the nutrients in the digestive tract, which plant do once they are out.