Evolving Trope

Tropes are based upon very well-founded principles of storytelling. But, as society changes, tropes may fall out of favor, either through association with something no longer considered acceptable, or from simple overuse and falling into a cliché. At that point, a subversion of the original may rise up to become the new standard, and the original will be slowly forgotten.

This is not a Cyclic Trope; the original trope probably isn't going to come back, for one reason or another.

Animals

 * Folk tales often portrayed wolves as evil, rapacious animals that preyed upon innocent livestock and humans. As the Industrial Age progressed, the wolves were no longer a threat, the people realized that wolves only kill to survive, and they're now portrayed as proud, majestic protectors of nature or just trying to feed their babies.
 * Although the truth is actually somewhere in between (wolves aren't as saintly as they tend to be depicted these days, and they did kill livestock and, at least in Europe, the odd person)
 * The same goes for many other wild animals. Bears used to be considered so scary that people even avoided saying their name, to the point that people in the early 21st century don't even know what the name was. The word they used to use in place of their name was "bear." The fact that that word has now become the animal's actual name, and that we use it without fear, is a good demonstration of how much the trope has evolved. While bears still tend to be portrayed as ferocious, it's often justified by them being a Mama Bear, and anyone trying to kill them is portrayed as the real villain.
 * It used to be that cats were portrayed as evil in literature and society in Europe and later North America. For the most part they are portrayed more positively or neutrally now.

Ethnic and National Groups

 * Portrayal of Germans in Film:
 * At first every German, from civilians to Gestapo, used to be monochromatically evil. (This applied to World War I, as well.)
 * As Communists emerged as enemies and West Germany an ally in the real world, WWII movies redefined it to just Nazis being evil, most civilians became either resistance or misguided Nazi sympathizers.
 * Further redefined in that Nazi-era German soldiers could be decent people and not just Faceless Goons; but most SS and Gestapo still have souls blacker than night.
 * The Onion points out an example. African Americans were thought to be unable to compete at sports in before Jackie Robinson, now in the United States, it is assumed that African Americans are better at sports than others.
 * The Polish used to be the butt of many jokes ripping on their supposed lack of intelligence. Due to wanting to prove all those idiots wrong, a lot of Polish people have become fiercely intellectual, resulting in them becoming one of the most intelligent ethnic groups around. This has actually started to seep back into media: Nowadays, you see someone in something who's Polish, they'll probably be a genius. This can result in Unfortunate Implications, since if you're of Polish descent and you just happen to be simple-minded, you'll get hell from everyone: bigots will mock you (and feel justified in doing so), and fellow Poles will despise you for making them look bad.
 * This is not so likely in any recent portrait of Polish people in Western Europe shows. Since the European internal borders were opened, West European countries have seen a massive influx of Polish people seeking simple labour for relatively high wages.

Organizations

 * Before the '60s, the government, in film, was pretty much portrayed as unequivocally good. The portrayal of corruption has become more and more common, though as Patriotic Fervor rises, it may lapse back for a time.
 * Even the subversion itself has evolved: the late Sixties saw liberal contempt for the U.S. government, but in the Seventies conservatives started to exhibit anti-government attitudes. By the Turn of the Millennium, antiestablishment factions were present on both ends of the spectrum, and they wax and wane in influence depending on the political alignment of whoever is in power at the time.
 * Similarly, it was forbidden — by strength of Executive Meddling — for American TV during The Sixties to depict Big Business as corrupt or evil. (For instance, the Klingons made their second appearance in Star Trek: The Original Series because writer David Gerrold was expressly forbidden by NBC Standards and Practices from having an evil corporation behind the sabotage of Sherman's Planet in "The Trouble With Tribbles".)  By the middle 1970s, though, evil companies and Corrupt Corporate Executives had begun appearing on American TV, and by the 1980s they were the default.  It is unlikely that American audiences will ever be innocent enough to accept an entirely benign/benevolent corporation in any media again.

Professions

 * Portrayal of scientists in Film:
 * In Science Is Bad movies, they were at best Mr. Exposition. More often, they were the villain, a la the Evilutionary Biologist.
 * This slowly changed, from an unheroic mentor into an active part of The Hero's posse.
 * This is more of a Cyclic Trope though — a lot of pulp stories (and even earlier Victorian stuff) had a Genius Bruiser protagonist.

Others

 * Many students of mythology will tell you that depictions of the gods and goddesses in human stories underwent a complex metamorphosis over time: from freakishly inhuman beings, to anthropomorphized monsters who were needlessly cruel to humans, to despicable caricatures illustrating various vices, to bumbling yet lovable clown-figures, and finally to heroic beings who protected mankind from destruction. Some anthropologists attribute this gradual shift in attitudes to a parallel shift in how the Greeks and other ancient peoples regarded authority, social mores, and the universe itself.
 * Computers were originally depicted as house-sized switchboards covered with Blinkenlights and full of vacuum tubes. Later on, they began using transistors and sported reel-to-reel tapes spinning in the background. Still later, they used microchips, got much smaller, displayed their information on monitors and stored data on floppy disks. Right now, they're small enough to fit in a pocket and stay connected to the outside world. Who knows what's next?