We do have a real life example of the DE-evolution of society. When Rome fell and the world went into the "dark ages," I'm sure that many folks had a sense that things at one point were better as they looked at the abandoned cities and the amazing achievement. Also science went backwards.
That's a myth that was largely promoted by Enlightenment age philosophers, authors, and historians. Science never went backwards, and many of the technological principles developed in the Greek and Roman empires continued to be used and improved upon; never mind the arrogance of thinking science and technology ended at the borders of the Roman Empire --The Middle East, India, China, and the empires of the Americas produced countless advancements as well.
There were many new inventions which drastically improves the lives of people in the Middle Ages, including:
Collars and harnesses for horses which allowed them to pull heavier loads and larger wagons without injury and with greater speed. The iron horseshoe protected their hooves and allowed greater traction. Paired harnesses allowed the horses to be arranged in groups of two in a line instead of all of them side by side, and thus allowed a greater number of horses to be used at once. The collar and harness allowed for the development of the furrow plough with adjustable plowing depth, which created an agricultural revolution.
Wind and water power were harnessed like never before, even during the Roman Empire with their aqueducts. Water powered mills allowed for industrialized sawing, grinding of grains, clothmaking, papermaking, blacksmithing, drawing wire, etc. Waterwheels were everywhere and allowed individuals villages a degree of autonomy they had never seen before. In places without accessible rivers and streams, windmills allowed for milling, the grinding of grain, and the pumping of water.
Eyeglasses were invented and allowed people to work longer, learn better, and have greater safety both at home and work.
The mechanical clock was invented and allowed precise scheduling and coordination of activities across great distances for the first time.
The Middle Ages were a time of great new universities, massive cathedrals, poetry, art, literature, and science. Yes, they had their ignorance and superstition just as any age does, but there was not a de-evolution of society as the myth suggests, and it's sad to see it still persists.