Everyone expects brothers and sisters to squabble as children. But what if you're both grown up and you still can't stand the sight of each other?
Are adult siblings who fight still playing out the resentments and frustrations they felt as children? Or is it just a case of a personality clash, pure and simple?
Even famous brothers and sisters fall out. Actress Julia Roberts and her brother Eric reportedly haven't spoken to each other for more than a decade.
After Julia's Oscar nomination for her role in the hit movie Erin Brockovitch, Eric accused her of betraying him by refusing to accept he'd been abused by their mother as a child. 'I grew up in a very dysfunctional home,' he said, when talking about their relationship. 'Everybody hated each other and made it clear.'
Then there are Oasis stars Noel and Liam Gallagher, never afraid to air their less-than-brotherly feelings.
Even the rarefied world of the Booker prize was rocked by adult sibling rivalry when warring authors Antonia Byatt and her sister Margaret Drabble were at loggerheads after Byatt won the prize in 1990.
Personality clash
Child psychologist Dr Pat Spungin, author of The Parentalk Guide to Brothers and Sisters (Hodder & Stoughton, £5.99), says that it's unusual, though not unknown, for some siblings to hate each other from the moment they first set eyes on each other - in short, a personality clash.
More commonly, there is a reason for the dislike many adult siblings feel for each other. Usually, it has its roots in how they were treated as children.
'One of the most common causes for adult siblings to dislike each other is where they have been compared by their parents as children,' she says. 'If you live in a family where you are always being compared with the others, then that will stay with you forever.
'When adult siblings don't get on, what commonly happens is they have a major 'falling out' over something apparently quite trivial. In fact, the trivial thing is just a cover for a much deeper issue, usually to do with favouritism, that still hasn't been resolved from childhood.'
Dr Spungin says comparing one child to another is damaging - and something every parent should try hard to avoid if they don't want its effects to last until adulthood.
'The tactic a lot of parents employ to sort out a problem is to make one child feel less capable. This is always unnecessary,' she says.
'If I want my child to stop being a whiner, I shouldn't say: 'Why can't you be happy, like your sister?' I should just deal with the issue of the whining, without reference to her sister.
Building barriers
'Comparing makes your children into competitors rather than allies. Telling one he's much better at making friends than his sister or the other she's much better behaved than her brother builds up barriers between them.'
The way parents react to the birth order within the family can also affect the children's attitudes towards each other. If the oldest child is always expected to be the sensible, responsible one, the middle child the easy-going peacemaker and the youngest the indulged baby, then those attitudes can stick and cause lasting resentment among the siblings.
So can adults do anything to make sure that their children will grow up liking, not hating, each other? Pat Spungin offers these tips:
1. Pay attention to the fact that you can make a difference to how your children will feel about each other. Don't compare them.
2. Speak very positively about what it means to be a brother or sister, and how valuable family life is.
3. Ask them and expect them to look after each other outside the home.
4. Remind them that blood is thicker than water and there are always people in the family they can turn to.
5. Doing things together is the key to bonding between siblings. As often as you can, make time to talk together, go out together, watch TV together, eat together and recap the day. That way, brothers and sisters stay in touch with each other's lives.
6. Celebrate each other's achievements. If oldest brother has done well in his exams, you all go out for a celebration meal; if youngest sister is running in an inter-schools tournament, you all turn out to cheer her on.
7. Learn to stand back. As long as there's no danger to either of them, resist the temptation to get involved in children's arguments. Parental interference always makes things worse, mainly because of all the extra attention. Leaving them to their own devices usually lets the row peter out.
Ultimately, Pat Spungin feels that, however difficult the sibling relationship, what matters most is the fact it exists.
'It doesn't matter that our siblings might not be the material of our best friends,' she says. 'What's important is that you share a long history. They have been in your life so long that it gives you the connection - with your past, with your roots. It is the longest relationship in our lives and that, in itself, counts for a lot.'
• Dr Pat Spungin is founder of the website raisingkids.co.uk
