You and your siblings played together, ate at the same table and slept under one roof, close as pages in a book -- or at least that's how you remember it. Yet nowadays you hardly ever see your adult brothers and sisters and, when you do, you have little to say to them. Somehow, and almost without noticing, you've drifted apart and the old loyalties are no longer there. So what happened?
According to the research, only about one-third of siblings remain very close into adulthood. Another third remain relatively close, and, while few adult siblings sever ties completely, about 33pc drift apart, sometimes describing their relationship as distant or rivalrous.
Often adult siblings can find they have little in common and, even when they spend limited time together, push each other's buttons without knowing why or how.
It's partly about being locked into old childhood patterns, says Dr Deirdre MacIntyre, director of the Institute of Child Education and Psychology Europe.
"Often we fall back into default childhood roles and that can cause trouble. The youngest child is perceived as leaving responsibilities to the others and the eldest plays the martyr or the bossy older sister role.
"We fall into these old scripts without understanding that we're at a different stage in our lives and that our relationships need to be more equal."
One reason siblings may not get along when they grow up is because they've failed to "re-negotiate" new adult roles and ways of relating to each other, she says.
Where relationships have been successfully "re-negotiated", they generally remain strong. "It has to be a relationship of equals."
However, sometimes your rosy memories of growing up together in one big close happy family can be surprisingly inaccurate, says child and adolescent psychologist Dr Kate Byrne.
That feeling of closeness may well have been based on little more than growing up under the same roof. The lack of a real, profound, bond can be camouflaged by the hustle and bustle of family life, she explains.
"You have situations where siblings' commonality is that they are brought up in the same house. When they grow up they find they have nothing in common.
"They might have got on okay when they were young. What often happens is that in some cases the only real link is the fact they grew up together and emotionally and psychologically that was the only common link."
In actuality, she says, they can be very different people without anything profound between them.
"That's what happens with a lot of siblings," she observes.
You choose your friends, points out Dr Byrne, not your siblings. When you grow up, she says, you may find that a brother or sister is not the person you'd choose to spend time with, even though you may have assumed a common ground based on your blood relationship.
"I have a younger sister who lives abroad and is a lovely person, but we have nothing in common and hardly ever see each other. If something happens we'd phone each other but we wouldn't be friends. I think this is quite common."
Sibling relationships are extremely complex and are also often affected by changing lifestyles.
"Sometime siblings move apart because they have very different lives -- they may live in different parts of the world and have different influences," says Dr MacIntyre, pointing to the trend in the 1950s where siblings who emigrated to the USA and occasionally visited home were perceived as "returned Yanks".
"You can also get a divide in terms of values. A sibling may adopt the value system of a new partner or culture or partner's family.
"These can be different and competing values that can put a distance between siblings. Experiences outside the relationship can either support that relationship or cause distances."
Sibling relationships can be quite fluid, changing dramatically as the years pass. Key life events such as college, career success, getting married, grieving, can bring adult siblings together or reinforce old rivalries.
Dr Byrne's eldest sons didn't get on for years but now, aged 21 and 19, they have been brought together by what she describes as "college and the challenges of life".
"The dynamics of siblings can change and sibling relationships keep changing, so there is hope if you don't get on with a sibling.
"We have a very rose-tinted attitude towards sibling relationships -- they're supposed to be like 'The Waltons' but in reality it's about character and personality and the people you choose to mix with.
"Siblings also change gradually over the years due to life experiences and the people they're mixing with. Sometimes the sibling you thought you knew has changed into somebody you may or may not even like."
And, of course, as many a fairytale has highlighted, siblings can be ruthlessly selfish. Dr Byrne points to the case of a single woman with several older married sisters.
"She was left to look after their elderly mother, almost completely alone, apart from a very occasional night out. The others felt quite simply that her life was not as important as theirs. Because they had families they were quite ruthless and selfish about this and had no sense of loyalty to their sibling who was the youngest."
Even when siblings are apparently close, tasks like sharing responsibility around elderly parents need to be negotiated openly and explicitly, warns Dr MacIntyre, otherwise some people feel they're left to do everything and resentment grows.
Then there's the kin-keeper -- often a characteristic of large families. This person is the one who keeps everyone together, she says.
"The kin-keeper keeps in touch with everyone in the family. This is the pivotal person who is the glue in those sibling relationships."
The kin-keeper, however, can struggle in the face of geographical distance, new relationships and family commitments as siblings become more committed or invested in their own new families, work and social life.
Recognise when you're flogging a dead horse, advises Dr Byrne.
"If you find that you are the one who is always trying to meet up with a sibling who doesn't seem that interested, it may be time to review the situation. Ask yourself would you do the same for a friend who has changed in this way or would you call it quits?"
Sometimes, however, the distance between siblings has its roots in parental favouritism, which is highly destructive and can lead to damaging resentment and rivalry between children, says psychotherapist Cathy Breslin.
"When there is a child who is admired and extolled by the parents as a star child, it can definitely cause underlying resentment."
This ill-feeling festers as the children grow. Later in life, when something major happens -- such as the death of a parent and the reading of a will -- old feelings of resentment can resurface.
"This goes on in the background during childhood and even though children might feel they are getting on well together, it is simmering there -- children learn what they see as opposed to what they are told and they will see the favouritism and feel resentment even though they may appear to get on."
In adulthood, she says, this can manifest in distancing, or a lack of trust.
So while a star child gets on with life and does well thanks to the self-esteem and confidence built up as a result of their parents' admiring attitude, feelings of inferiority can persist for other children.
The feeling of being 'less than' often persists into adulthood, warns Ms Breslin, causing difficulties in sibling or social relationships and turning children into adult people-pleasers.
Although some children in this position may try hard to build a relationship with other siblings, including the star child, others will keep their distance until a big family event like a will reading brings hidden resentments to the surface, she says.
Longstanding unacknowledged grudges and resentments can also result in long silences throughout adulthood.
"A lot of these things have to do with unfinished business many years previously in things that happened and were never spoken about."
But do we really need them anyway?
If you're feeling left out by your siblings, ask yourself why you're so dependent on them to make you happy, says psychologist Domhnall Casey.
"People drift apart, live abroad and have other preoccupations which become more immediate and more important than their siblings.
"Why are you so dependent on your siblings to make you happy?"
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