Bastards aren’t the inevitable consequence of adultery, but they’re pretty common.
They don’t have to be, of course. With birth control, one can have oodles of standard-issue heterosexual intercourse without ever producing a child. But the kind of society that stigmatizes bastardy — being born out of wedlock — is often the kind of society that doesn’t practice much in the way of contraception, either. The connection isn’t accidental; patriarchy usually demands both that women produce offspring only for their legally recognized husbands, and that they produce offspring.
That “bastard” is a term of deep stigma is clear from the fact that it survives in English as a pejorative, long after we stopped using it to describe out-of-wedlock children. We as a society may tut-tut the “problem” of single mothers (a phrase that covers not only unmarried women, but widows and divorcees with minor children), but that’s more about economic stability or the notion that children should have one male and one female parent than it is about the child’s conception. While specific groups may feel differently, the general zeitgeist in the West doesn’t see such a mother as a “fallen woman,” nor does it assume the circumstances of conception transferred any effect to the child.
But oh, was that ever not the case in the past. It’s extremely common for people to believe that moral traits are just as heritable as physical ones, and some of those traits are pseudo-Lamarckian: anyone conceived in sin is stained by it. In this view, a bastard naturally lacks moral fiber, because his parents tossed theirs aside when they made him. He might be more prone to lust, or to lying, or to envy, or to treachery. I mean, just look at Mordred! (Incest and adultery: a double whammy of sin.)
Where bastardy is considered an important issue, the law takes a great deal of interest in regulating the situation. The practice of child support or child maintenance, where the father is required to contribute toward the expense for rearing their offspring, isn’t a new innovation; after all, financial punishment is a time-honored response to violating laws and social norms. Of course, that requires you to know who the father is — and without genetic paternity tests or magical equivalent, proving that might be easier said than done, especially if the father is influential. Whether he bothers to uphold his obligation is also an open question.
Additionally, the law often takes steps to enshrine the stigma attached to that status. George R.R. Martin’s notion of regional surnames for bastards (Snow, Sand, etc.) is more elaborate than anything I know of in the real world, but it’s very common for illegitimate children to be barred from using their father’s family name. Furthermore, an illegitimate son is frequently ineligible to inherit his father’s estate, even if he’s older than his legitimate half-siblings. In that sense he shares a great deal in common with the son of a concubine, even when concubinage is a legally recognized relationship.
It isn’t necessarily the case, though, that once a bastard, always a bastard. (At least not in the legal sense.) In some jurisdictions, an illegitimate child can be legitimized by his parents’ marriage, sometimes with the restriction that they must have been able to marry at the time of his conception — meaning no such luck for anyone born of an adulterous affair. Other cultures might allow for the formal adoption of illegitimate offspring, granting them legal status via another route.
In the absence of such elevation, though, the outlook for a bastard may be bleak. If he’s criminal or covetous, it’s less because he absorbed that tendency through the placental barrier, and more because he spends his life disenfranchised. He grows up seeing what his legitimate half-siblings get to have, or he’s abandoned to be raised as a penniless foundling by a religious or charitable institution. Or he does have one parent, usually a mother . . . who may have been thrown out of her home by an angry father or a divorcing husband, leaving her to survive however she can.
You may have noticed that I’m saying “he” a lot more than “they,” the way I normally would. That’s because society tends to get a lot more worked up over bastard sons than daughters. The latter may be in for as much pity and disdain as their illegitimate brothers, and just as vulnerable to the accusation that any moral failings are inherited from their parents (their mothers especially), but again, patriarchy: this issue becomes the most fraught when inheritance is patrilineal. A son is a threat to the family line; a daughter is not.
And that’s been a real issue at countless points throughout history. Whatever the law may say about bastards not inheriting, swords can say something different — especially when there are factions that see political gain in backing a different contender. Ambitious upstart or hapless pawn, a bastard son may have a very interesting future.
Mostly at the highest levels of society, of course. As with adultery, status matters: history is littered with royal bastards, some of whom were open secrets, others not even that concealed. More than a few kings have acknowledged their bastards and bestowed titles, wealth, and even land on them, or married them into good families. You’ll receive relatively little stigmatization then, given the benefits of association with even a by-blow of the king. Mind you, that’s still an uncomfortable place to be, especially if you’re a son; you never know if your legitimate half-brother the heir is going to decide to clear the board of rivals.
I want to close with a quick tour through some of the English terms for this situation, because they shed a fascinating light on how we view it. Unsurprisingly, the Oxford Historical Thesaurus lists over thirty synonyms, and that’s not counting phrases like “born on the wrong side of the blanket” — meaning not conceived in the marital bed, where such things ought to occur. Illegitimacy refers to the individual’s status in law, which is why it can be removed through legal remedy; something like “base-born” points more toward social class (since it can also just mean “of common birth”), and implies that even if you’re elevated to a higher status, your origins aren’t going away. The same is true, even more pejoratively, of a term like “misbegotten.” Conversely, the more modern phrase of “love child” casts the situation in a romantic light. But I think my favorite euphemism is “natural child.” I suspect it’s meant in negative contrast to civilization, i.e. the parents have given in to their bestial instincts . . . but it always makes me wonder if there’s something unnatural about the children conceived in wedlock!