They do indeed have friends and families. However, what happens when you catch one depends on the species.

Many pokémon actually don’t form tightly knit communities, so if they lose one member, they by and large don’t notice. For example, the fields of Kanto are rife with rattata who had left the woods in search of food. The rattata are by and large independent, so if you catch one, the others will simply continue foraging as if nothing had happened. The most they might do is avoid you, but otherwise, they exhibit no change in behavior. If one had young, then the others will simply adopt the abandoned hatchlings or leave them to die. This is, of course, taking into consideration the fact that there is always a risk that the younglings of these pokémon will die anyway, as it only takes a few minutes for predators to raid their nests—which is to say the death of a litter of hatchlings might actually be inevitable if the pokémon has ventured so far from its nest to leave it perfectly exposed to the wild.

Other pokémon never venture away from their nests anyway unless they intentionally wish to leave home. Take clefairy, for example. Clefairy form vast, closely-knit communities, but these communities are well-hidden deep within mountain ranges and cave systems, in places that are nigh inaccessible to humans. Additionally, many pokémon and animals between the clefairy nests and human-accessible parts of these cave and mountain systems eat clefairy or at least will attack them on sight, and clefairy themselves are weaker pokémon not particularly well-suited for battle. Thus, any clefairy you stumble across in the wild is usually one that is dead-set, for whatever reason, to leave home. (Why this is, researchers aren’t quite certain. Some clefairy are curious about the outside world; others wish to get stronger through training.) Thus, it’s morally acceptable to catch these pokémon, as they’re actually far, far from home and very likely have already said their goodbyes.

Conversely, if you do find a clefairy colony or the nests of other pokémon that behave like clefairy, it’s highly recommended that you do not attempt to catch one. The general rule is the larger the group of pokémon, the more likely you’ll want to leave them alone, as taking one will only give the others time to put together an argument as to why you should let their friend go. And by “put together an argument as to why you should let their friend go,” I mean “attack you en masse.” (One clefairy may be ill-suited to battle. Thirty upset clefairy, however, are not.)

And of course, other pokémon are a combination of the two groups mentioned above. They live in flocks or herds that operate in close-knit communities, but they actually don’t mind if you take one of their numbers (unless in the rare case that they do). These pokémon rely on their numbers to defend themselves, and they expect you to understand that the volume of their group is a threat. Many bird pokémon fall into this group, with examples such as pidgey, taillow, and spearow being the hallmarks of this behavior. All of them live in flocks, so if you encounter one, it’s very likely that a few dozen of its friends and family are very close by. However, if you catch one, then very likely, that few dozen of its friends or family won’t mind. (Why this is comes down to the fact that most pokémon understand there are benefits to forging relationships with humans.) On the other hand, if you attempt to catch a spearow, and the other spearow feel strongly about not parting with their friend, they will let you know … by also attacking you en masse.

In short, this is why it’s a good idea for trainers to exercise extreme levels of caution when dealing with wild pokémon. Many will allow you to catch them, yes, but there are several that will not. You’ll be able to figure out which is which simply by observing them and watching out for others like them. If it looks like it or its friends feel threatened by your presence, leave them alone. Finally, always remember that pokémon are absolutely capable of defending themselves, especially in groups.

Although there are a number of people in Johto who claim to be “pokémon speakers,” or those who can speak with pokémon, and although there are a few pokédex entries that imply otherwise, in truth, most pokémon can understand human speech just fine. It’s just that most pokémon—especially wild ones—respond better if a human attempts to speak with them in their “native language.” However, this is just because it’s easier to hold their attention this way; if you attempt to hold any sort of conversation with a pokémon, they should have no problem following what you’re saying.

Of course, things get complicated with languages, but for the most part, this is one of the reasons why we converted to an international language with the establishment of pokémon leagues. The other reason, of course, is because it’s easier for trainers to enter foreign leagues if they didn’t have to deal with a language barrier. This is why it’s easy for a ten-year-old from Japan to enter the Unova League.

For pokémon, meanwhile, it’s less of a chore to translate what humans are saying because we, for the most part, are speaking only one language, and that language was itself constructed from a pokémon tongue. This language, for those who are less well-versed in etymology (I know we don’t normally teach this in school for whatever reason) is Common, which is a language based entirely on the unown. For this reason, pokémon are capable of latching onto what we say because in a way, we are speaking one of their languages—just not their native language. (This is why we can’t exactly understand them unless we make a concerted effort to do so. Johtonian pokémon speakers rely on this fact in order to perform, but all they’re really doing is making more of an effort than most people to listen.)

Of course, it’s entirely possible for a human to speak one of the old languages such as French or Japanese, but this tends to cause more confusion than it’s worth, especially given how interconnected we are as a species at this point.

So long as you’re engaging in league-sanctioned battles or battles against wild pokémon, they’re perfectly safe. There are strict rules within every pokémon league that prevent trainers from killing or seriously injuring opponent pokémon. It’s like boxing or wrestling: in legitimate matches, you absolutely cannot do permanent damage to your opponent, as any more than that constitutes manslaughter or even murder. The same concept applies to league-sanctioned battles. While you can’t be blamed for acts of God (although in some cases, the architect of the stadium might be), if you consciously attempt to disobey the referee and continue the match past the point where your pokémon or your opponent’s has fainted, you could be arrested after the battle if anything serious happens. However, if you engage in a league-sanctioned battle, you will either do so under the watch of an official referee (who will always call the match before any serious damage occurs), or you will outline the rules to a fellow trainer beforehand (so the both of you enter a verbal agreement to fight while following league regulations).

As for wild pokémon battles, wild pokémon typically have no interest in killing other pokémon except in extreme cases of self-defense. Wild pokémon are intelligent enough to recognize when an enemy has been incapacitated, and thus, they will leave you alone if you make it apparent that you won’t harm them after the match is over. (Note: For the most part. Some of the more aggressive pokémon or pokémon who believe you’re trying to kill them will make an attempt on your life and the lives of your pokémon, so it’s a good idea to exercise good judgment while in the wild. Do not, for example, attack a singular spearow, as spearow are just ornery and violent enough to call the rest of their nearby flock to attack you back.)

That having been said, there are also underground pokémon matches, or battles between trainers in settings that aren’t exactly by-the-book. You’ll know when you’ve found such a place when trainers never outline rules to one another or when large crowds gather to take bets on the matches. These matches are usually done to-the-death, and thus, they’re far less safe for either the pokémon or the trainers involved. Needless to say, they’re highly illegal and frowned upon by most societies, but due to their underground, secretive nature, it’s difficult to prevent them from occurring. The best advice I can give you regarding these is never battle in an arena unless you know for certain that it’s league-approved, and certainly don’t battle against a trainer who agrees to league rules beforehand.

Allow me to use a metaphor to explain.

Let’s say it’s the middle of summer, and you put a group of human beings in a room with no air conditioning. All of these humans are physically the same species, but some tolerate the ensuing heat more than others. On one extreme of the spectrum, you have the people who are perfectly fine sitting in a hot room. On the other, you have the people who become lethargic and moody—even a little sick. Everyone else is somewhere in between.

Types are like that. You may have a number of pokémon that are all the same type, but not all of them will express the type’s signature weaknesses and resistances the same way. For example, some rock-types take fire-type attacks without flinching, while others feel visibly uncomfortable by proximity to heat. Conversely, magnemite and a number of other steel-types absolutely hate heat, but lucario and more mammalian species are more capable of tolerating it (so long as they aren’t exposed to direct fire). This is why it’s often difficult to pinpoint a pokémon’s type.

Also, think of it like any other element of taxonomy. Yes, to researchers, pokémon types are merely another form of taxonomy, or classification of living organisms. With the broader classification of organisms, system used by modern scientists splits all organisms into seven kingdoms: Bacteria, Protozoa, Chromista (for algae), Plantae, Fungi, Animalia, and Pokémonica. Sixty years ago, however, there were only four kingdoms, as scientists grouped algae and fungi with plants and pokémon with animals. As our understanding of the world grew, we realized that this system was insufficient to describe the organisms we were studying, and so, the system changed to fit our needs. Types, being another form of taxonomy, are just as fluid as the grand system of taxonomic ranks.

That is to say, although we researchers do our best to classify pokémon accurately, sometimes, our way of describing them needs to change due to newly acquired information. The fairy type is actually an excellent example. The pokémon that have been reclassified into that particular type have a wide variety of offensive and defensive capabilities, as well as a variety of secondary types, all of which made it difficult for researchers to notice that they shared any characteristics between them.

For example, clefable and wigglytuff are both hardy pokémon, but because of that, both are able to withstand venomous attacks far better than a number of other fairy-types on record. As such, scientists didn’t realize either of them had a weakness at all until their battling abilities were compared to other normal-types. (In actuality, it was only recently pointed out that both types weren’t simply tolerating Dragon Claw and other dragon-type attacks due to their hardiness; they were quite simply immune to dragon moves. After that, a full-scale study was done on them to determine why.)

Conversely, gardevoir is a far more fragile pokémon than clefable and wigglytuff, and as such, it was originally thought that its weakness to both poison and steel can be easily explained by its lack of defensive capabilities. It certainly didn’t help that its secondary type could easily dispatch both poison and fighting—the latter of which gardevoir boasts a double resistance to—making understanding the abnormalities of the species’ weaknesses and strengths particularly difficult to understand. It was only after we had compared gardevoir’s ability to withstand bug- and dark-types to gallade’s that anyone had realized that perhaps there was something else going on.

The point is that the type classification system is a classification system first and foremost. Each pokémon within every type actually has differing tolerance thresholds when it comes to withstanding other elements. Even clefable and granbull—both mammalian pokémon who were reclassified from pure normal-types to pure fairy-types—don’t handle poison and steel moves in the exact same way. Ultimately, however, whenever the scientific community obtains new information that sheds brand-new light on a group of pokémon, we change the classification system as necessary.

If by “official artwork,” you mean photographs in the pokédex, absolutely. The pokédex images are merely photographs of the specimen a trainer or researcher has on hand. Actual wild pokémon may possess markings that might vary greatly due to a number of factors, including environment, certain genetic factors, physical condition, and so forth.

More specifically:

• Pokémon may change colors in response to their environment. This not only refers to adaptive evolution but also individual response to environmental influences, including the chemistry of the available food sources. For example, even visiting pokémon to Pinkan Island in the Orange Islands archipelago have been known to turn pink due to the fact that pinkan berries—a rare, pink berry that happens to be high in lycopene—are the most reliable food source for pokémon on the island. (On that note, it’s highly recommended that trainers feed their pokémon commercially produced kibble while on the island unless they want a pokémon the color of a jigglypuff.)
• But yes, evolution is also a possibility. Take the Alolan and Kantonian vulpix, for example. Vulpix in Kanto have adapted to warmer climates, and hence, they possess a fire-red coat of coarse, short hair. Alolan vulpix, meanwhile, thrive primarily in colder, snowier climates. Thus, they sport snow-white coats that allow them to blend in with their surroundings, and their fur is thick and soft enough to trap the heat they need to survive cold, wintry nights.
• While pokémon inherit the species of their mother (unless that mother is a ditto), it’s not at all unusual for some to inherit traits from either parent. It’s not normally so drastic as to produce pokémon that are entirely a different shape or color than the ones you might see in your pokédex, but as an example, a meowth whose father was a pikachu may have more golden fur than normal, whereas a meowth whose father was an eevee may have thicker fur around the neck and a bushier tail. In short, the meowth will still be immediately recognizable as a meowth, but certain traits may be slightly different from the official photograph thanks to its father.
• Pokémon fur, skin, and so forth are notably more vibrant the healthier the pokémon in question is, and likewise, fur will usually be thicker and shinier. By contrast, duller, grayer, or thinner fur or skin indicates a general illness. Likewise, pokémon with unusual spots, lumps, or moles may be suffering from cancer, cysts, or other unfortunate conditions, and pokémon can certainly be born with deformed limbs. Alternatively, some injuries sustained on the battlefield or elsewhere may lead to permanent damage, such as scars, missing eyes, torn limbs, and so on. Old age can also bring about arthritis, which in some pokémon pronounces itself via enflamed joints. If your pokémon suddenly changes in physical appearance or if you have a pokémon with any physical condition that seems a little unnatural, it’s best to take them to a pokémon center for an examination.
• Of course, these are just a few of the most likely possibilities for an explanation as to how you might acquire a pokémon with unusual spots. There are certainly others as well, including the possibility that you’ve just encountered a specimen in a particularly dire need of a bath.