"And So to Bed" (originally published in Analog, January 1986) is the second story chronologically in A Different Flesh (It was also published in the short-story collection Kaleidoscope). It consists of a mock entry in the diary of Samuel Pepys, who, in OTL, kept a very lengthy journal that has proved invaluable to our present understanding of Restoration England.
In the story, set in May 1661, Pepys relates his decision to purchase two sims for his household. By watching these sims, as well as observing various other animals found in North America, Pepys develops the transformational theory of life, i.e. the Theory of Evolution, roughly 150 years before Charles Darwin was born, thus providing a concrete example of how the presence of the sims has changed how Europeans think.
Stylistically, the story is perhaps one of Harry Turtledove's stronger short works, as he captures the flavour of Pepys' writing quite well.