What constitutes incest?

Yes, that's an appropriate way of describing those relationships that develop when one partner has been in a professional/caring/parental/sibling role.

Isn't it a bit like the teacher /pupil issue? When one partner is in a position of authority / care and then develops a relationship with someone they are supposed to be caring for/ looking after ...it always feels that there is a possibility of 'taking advantage' and of manipulation of the (usually) youunger..though there have been cases of young female nurses marrying older incapacitated men.

It's not incest under UK law, but there may be some information that has concerned the authorities, if he was fulfilling the role of father when the relationship with the mother began and this girl would be a child. If there was a sexual relationship then, prosecution could be pursued, but why they would do it under the umbrella of incest, and not straightforward sexual assault of a child, is unclear. Perhaps their local laws define this situation as incest because they started with an establshed stepfather/stepdaughter relationship that has clearly been breached because they have a baby?

The whole Bill Wyman family thing is so unpleasant isn't it. I'm afraid my work experience makes me anxious about these families where boundaries are blurred - not healthy for children.

Didn't Bill Wyman's son marry his father's ex mother-in-law? There are some very bizarre relationships.

My brother-in-law has a daughter. His second wife has a son. The son and daughter have got married, its not incest but it is complicated, the daughter has an instant step mother and mother in-law all in one go.

My great grandma married her brother in law when her husband died.

My husbands great, great, uncle married his niece (brothers daughter) in the late 19th century. Don't know how they got away with it

Suppose what I was trying to say was that there was a biological kind of incest - as greatnan pointed out its a bad idea to marry relatives as you might both carry the same recessive genes and also a cultural definition of incest, which will vary hugely between cultures. Do we have any anthropologists in the house? e,g in a hypothetical culture it might be incest for a maternal uncle to pair up with his niece but fine for a paternal uncle, because of the way family relations are defined within that culture.
I think my GGF was quite old when he remarried, but again they were living under the same roof, so it may have been a way of making the relationship respectable?

I think there are some places when it is the duty of a brother to marry his widowed SiL. It provides a place in the society for the widow.

NOT saying I agree in current era but guess in the past it was a good thing to do!

A bit daft to regard him as her "step-father" really, when he is only seven years older than her.

I think it will be thrown out of court.

Well, it seems to be down to semantics. Being a father, whether biological or not, is about behaving in an appropriate manner. In this case, the step-father did not. Whether that should be considered a crime or not is a moot point. Boundaries have been broached in an unacceptable manner.
Consider the issue of adoption for instance.

Whether the relationship is inappropriate or not is one question, and I suspect, that there must be questions about that in this case, but incest it is not. Incest is having a sexual relationship with a close blood relative, usually mother/son, father/daughter, brother/sister. Generally if you are too closely related by blood to marry, sexual relations are described as incest

As JessM has said, there is something about needing to keep firm relationship boundaries in a family.
It would seem that she was only 16 when this guy married her mother! (I am not saying the relationship started then.) That marriage put him in the role of her Dad.

The mother was probably at least in her 30s when she married this guy who was then 23. I am concerned that this sounds decidedly inappropriate at the very least. I have a feeling that there might be more going on than we know about.
If it was suspicious he would not be the first guy who had shacked up with a mother to get too her children.

The more I write about this the more I think that this is "right out of order!"

My question was badly worded. I admit a crime is a crime but they seem to be using a sledgehammer to crack a nut with this one.

The list of 'a man may not marry' in the book of Common Prayer made interesting reading having to sit through sermons - when a child.

Incest has always been practised far more than is acknowledged

One of my GGFs did too, JessM Two of his sisters-in-law lived with them even before his wife died, so I suppose it made sense to marry one of them as she was already looking after the house and children. They went on to have another couple of children. I often wonder whether the third sister felt a bit left out - but perhaps she wasn't!

Oh yes! Arthur, wasn't he called?! [shows off scrap of knowledge brain has managed to retain)

Didn't Henry VIII do just that? (The other way round - his dead brother's wife)

Woody Allen also went off with an adopted daughter didn't he.
There is something going on here around maintaining boundaries within a family isn't there. Some incest laws go back to the bible.
In mediaeval times the aristocracy were supposed to get the Pope's dispensation if they were within 7 degrees if consanguinity. Which of course pretty much all the nobility of England and France were. (money spinner for vatican perhaps)
I seem to remember a family story that one of my GGFs married his sister in law after GGM had died and that this was, at the time, legally forbidden.

I can understand the question. If police resources are limited, it makes sense to pursue those criminals who are hurting other people/society at large.
Incest is illegal in the UK, but sentencing varies according to the circumstances, and whether there is any indication of undue pressure. The sensible reason for banning sexual relations between close family members is because the limitation of the gene pool can lead to deformed/handicapped children. Intermarriage amongst some Asian races have had this result, and of course, the royal families of Europe had many medical problems.

"Are there no other crimes in West Virginia so that it makes sense to spend all this time and money punishing two people for having a relationship?"

If there are or there aren't - how does that affect this case? Your question isn't logical...

How weird! I'm not sure that even real incest would be against the law in this country.