Historically, being born out of wedlock was significant as it deprived a person of his otherwise inheritance, which was usually the only way to acquire real property.
The Church recognized bastards if the natural parents subsequently married.
When England was just sorting out the new beast called a "parliament", the very first set of statutes (Statute of Merton, 1235) included consideration of a proposal by:
"... all the Bishops ... that all such as were born afore matrimony shold be legitimate as well as they that be born after ... as to the succession of inheritance, forasmuch as the Church accepteth such for legitimate. And all the Earls and Barons with one voice answered that they would not change the laws of the Realm, which hitherto have been used and approved."
... which suggests that for the old Earls and Barons, there might be some truth to the old joke:
- Q. How many natural fathers does it take to screw in a lightbulb?
- A. Lightbulb? What lightbulb? I didn't screw any lightbulb! It's not my lightbulb and I don't know anything about it!
The only advantage, sometimes, to being a bastard (except for geneologists), was that the bastard did not take his father's surname. They were considered born without any surname and could choose anyone they liked.
Bastards were of such a lower caste in medieval England that Latin expressions were developed just for them, labelling them "son of nobody, sons of the people".
Blackstone, in his Commentaries on the Laws of England (1765) said that a bastard "cannot be heir to anyone, neither can he have heirs" and could be legitimized only by "act of Parliament".
He added, on the subject of divorces, that:
"... the issue of such marriage as is thus entirely dissolved are bastards".
Other jurisdictions, though, accepted as legitimate the birth of a child before marriage if the naural parents subsequently married.
But at common law, bastards not legitimized by the marriage of their parents, were left empty-handed when their parents died (with one esoteric exception to do with real property which goes by the cool name of bastard eigné). As late as 1937, Eversley wrote:
"The rights of bastards at common law are not numerous and these, he must acquire for himself and cannot inherit."
By now, though, most nations (including England) have stated on the record that all children have equal rights, whether they are issue of a marriage or not.
Even in 1881, judge Hawkins wrote, in Hardy:
"I rejoice to see that since the days of Queen Elizabeth, our laws have been so far humanized that a bastard child is no longer a mere thing to be shunned by an overseer - whose existence is unrecognised until it becomes a pauper, and whose legitimate home is a workhouse, that it is no longer permissible to punish its unfortunate mother with hard labor for a year, nor its father with a whipping at the cart's tail; but that even an illegitimate child may find itself a member of some honest family, and that the sole obligation now cast upon its parents is that each may be compelled to bear his or her own fair share of the maintenance and education of the unfortunate offspring of their common failing."
The 1969 and then 1987 Family Law Reform Act of England is clear:
"In this Act and enactments passed and instruments made after the coming into force of this section, references (however expressed) to any relationship between two persons shall, unless the contrary intention appears, be construed without regard to whether or not the father and mother of either of them, or the father and mother of any person through whom the relationship is deduced, have or had been married to each other at any time."
BC's Estate Administration Act defines "issue" without reference to marriage; as "all lineal descendants of the ancestor".
All of this pales in the new usage of the word, a generic term, inspired by the vagaries of war (General Patton comes to mind), referring now to someone that is offensive or disagreeable.