Alfred Adler, an Austrian psychiatrist and former disciple of Freud, acknowledged environmental influences such as social class, geographic origin and relationship with parents as factors in the development of personality. But it was, he said, birth order and relationship with siblings that was the single most reliable predictor of human behaviour.
Joy Berthoud, author of a new book, Pecking Order, had read and been convinced by research confirming this. "But I am a journalist and I wanted to stand it up myself," she says. Hundreds of interviews later, she had her proof. "Without exception, everyone I spoke to displayed the characteristics of their position in the family pecking order."
But she is quick to point out that there are many variables, dictated most notably by age gap and the gender of the children. "A girl with a sister two years her senior will be closer to the model of the second child than a girl with a brother 10 years older, who might well display more of the characteristics of a first or only child."
As a first child, according to Berthoud, you will probably adopt some of your parents' behaviour and generally be quite "grown-up". You receive all their attention, but all their expectations are also heaped on you.
"When child number two arrives," she explains, "there will be a fear of the withdrawal of your parents' love and, more than likely, a noticeable reduction in the amount of attention they give you. This is when you will start to try to please adults, to become even more like them - conservative and responsible - in an effort to win back what you've lost. As you grow up, this can lead to feelings of never being good enough, but with or without this insecurity, you'll probably be a high achiever because you're trying so hard."
"I have one clear memory of my sister Jane arriving on the scene," says Julie, 31, a civil servant. "I was two and a half, and I climbed into her carry-cot when she wasn't in it and lay down. I think I must have wanted to be the baby again, and get all the attention she was getting.
"I was quite like my mum and dad - they're both teachers with a strong art bias, and I became quite arty, too," says Julie. "I went on to study graphic design. But Jane was into numbers and computers. She was also far more outgoing than me, with an active social life. I was less confident and much more level-headed and sensible."
Nicola Carter, nine, can remember clearly how she felt when her younger sister Felicity arrived six years ago.
"I didn't want to share anything with her," she says. "I suppose I've got used to it now. But I do get jealous when she gets something I want, even if she's saved up her money and I haven't.
"I'm quite serious really, but sometimes I do silly things, and people look at me. It annoys me that people expect you to be grown-up all the time just because you're the eldest.
"But it's good being able to boss the others around - and I don't get hand-me-down clothes," she says of Felicity and younger brother Elliot, aged four.
The second child is most commonly identified as taking the opposite line to their older sibling. Feelings of inferiority can inspire the second to outdo the first in academic areas, but they will usually find something else to be good at.
This position in the pecking order will also give you less respect for the established order, unlike the older sibling trying to be like the adults. There will be nothing to be gained from it. The behaviour of these children will, in short, generally lean towards that which attracts attention, and they will more than likely have a more relaxed attitude to life. Sibling rivalry is also common.
Felicity Carter, seven, is already at the sharp end of sibling rivalry with her sister, Nicola. "She's always being horrible to me; she kicks and punches me," she admits.
"She is better than me at things like maths. But we're both good at horse- riding. I'd like to be better than her at that, just to show her."
Felicity is a middle child but clearly displays more second-child tendencies. This might be because her brother, Elliot, four, is of a different gender.
Karen Gunn, 29, a writer and assistant on a magazine, has a brother, Douglas, seven years her junior. She also has a sister, Fiona, who is 31.
Middle children are often left feeling like the odd one out, not having the attachment to their parents that their older sibling has but also not being the baby of the family, with the incumbent attention heaped on it. This often provokes attention-seeking behaviour and can lead to depression or even paranoia in later life.
Karen admits she has always striven to be noticed. "I was always the crash-bang-wallop one of the family. Fiona was much more reserved and thoughtful when we visited relatives. I'd always be saying, 'Look at me, I can do a hand stand.' "
The youngest child doesn't have to worry about dethronement and can consequently focus on the road ahead with no distractions. He or she might well catch up with or even overtake older siblings. But equally, being pampered might undermine his or her ambition. Only children are similar in many ways to first children, but their behaviour is not modified by dethronement. Constant contact with adults gives them social maturity but emotional immaturity. The strong parental relationship can be supportive and encourage self-confidence, but it can also be claustrophobic. Only children may well leave home early.
Children in large families have fewer opportunities for individual attention and expression, but the care and company of their siblings often compensates for this. This support continues into adulthood.
Dale Beeson, 36, a lawyer and media agent, grew up one of five boys who range in age from 40 to 28.
"My brothers, with one exception, have ended up in white-collar jobs, whereas I went on to further education and a profession," says Dale. "I wanted to be different and it made me ambitious.
"There has never been any resentment because of it - my brothers tell me how proud they are of me. I know that whatever happens, I will always have their support."
Berthoud hopes her book will help people learn a little more about themselves and will allow parents to understand why their children may behave the way they do.
'Pecking Order' by Joy Berthoud will be published by Victor Gollancz on 26 September priced pounds 9.99.
THE GOOD, THE BAD AND THE SPOILT: HOW CHILDREN REACT
First-borns: Lots of attention, high parental expectations. Must then cope with dethronement by subsequent children. Try to win back attention by meeting parents' expectations.
Second children: Probably rebel against parental authority and goody- goody elder sibling. Rebellion could take creative form or result in child so laid-back it makes no effort.
Middle children: Enjoy no clear status, often searching constantly for a role in the family.
Youngest: Plenty of attention from parents and siblings. If spoilt can lack motivation.
Only child: Risks being parent-bound. Probably precocious and self-sufficient. May well flee parental claustrophobia early.
Large families: May lack parental attention. Support of siblings is compensation.
THE FAMOUS AND THEIR POSITION IN THE FAMILY
First born: Queen Elizabeth II, Cecil Parkinson, Geoffrey Boycott, Winston Churchill
Second born: Will Carling, Oscar Wilde, Charlie Chaplin, Lady Thatcher
Middle children: Damon Hill, Cindy Crawford, Robert Graves, Edward Elgar
Youngest: Laurence Olivier, John Major, Sir Jimmy Saville, George Michael
Only child: Gayle Hunnicutt (actress), Nick Faldo, EM Forster, Enoch Powell
Large families: the Kennedys, the Longford clan, the Osmonds
Twins: The Barclays (owners of the Ritz Hotel), the Krays, cricketers Alec and Eric Bedser.
Stepfamilies: Isabella Rossellini, actress, Robert Graves, George EliotReuse content