Knowing your place

It's 10 years since parenting educator Michael Grose wrote When First Borns Rule the World and Last Borns Want to Change It. Recently, he's been considering a sequel titled ''When birth order doesn't apply''.

Birth-order theory, which has been around since the late 1800s, posits that the family position you are born into, leaves an indelible mark on your behaviour and personality. First borns turn into responsible leaders, middle children into diplomatic negotiators and last borns become charming challengers of authority. These stark differences in personality are explained by differences in parental attention and interaction with siblings.

Common changes in family structure, such as an increase in single-parent households, step-families, blended families and smaller family sizes with one or two children, can create mixed effects. "If there's a big gap before the youngest is born, that last born can become like a first born, receiving similar levels of parental attention," Grose says. "If the first born is a boy and the second born a girl, and if the age gap between them is small, the girl can end up more like a first born, due to girls' earlier maturation. In blended families, you can get children jostling to keep their position. The position a child is most reluctant to give up is being the youngest."

It's not that birth order is irrelevant, Grose says, it's just one filter to apply to family dynamics. "Regardless of family size or structure, you'll still get children trying to carve out their niche - if someone is already the responsible one good at school, then the next child will specialise in something else. And there'll still be the influence of parental experience, with first-time parents prone to placing more pressure and anxiety on themselves and their first child." Parenting tips, such as ''ease up on your first born'' and ''make sure you spend one-to-one time with middle children, who can feel ignored'', still count as sound, commonsense advice.

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Is birth-order effect real? While decades of research exists that seems to confirm the effects of birth order, much of it is flawed by failing to take into account confounding factors such as family size and socio-economic factors, according to Dr Joshua Hartshorne, a postdoctoral fellow at Massachusetts Institute of Technology.

"There is compelling evidence though, that eldest siblings tend to be (very, very slightly) smarter than their younger siblings. There is also recent evidence that eldest siblings do better in school, and that younger siblings are more likely to be risk takers and get into trouble at earlier ages."

Hartshorne's research has demonstrated that birth order affects relationship choices. "In two large surveys, we found that people are more likely to form close platonic and romantic relationships with other people of the same birth order. First borns were more likely to associate with first borns, middle borns with middle borns, last borns with last borns, and only children with only children. This is most likely due to effects of birth order on personality. Contrary to popular perceptions, same personalities attract."