WEALTHY parents are making their first-born the focus of family ambition, giving them a disproportionate share of time, care and attention, according to research. Younger siblings, by contrast, are being held back in their lives by a relative lack of attention.

The findings show affluent modern couples are aping the upper-class tradition of primogeniture. Although poor families also show some extra favour to the oldest child, this practice is far more pronounced among those who are richer - despite there being more resources to share with younger offspring.

“Traditionally, aristocratic families tended to give the first heir more wealth,” said David Lawson, a behavioural ecologist with the human evolutionary ecology group at University College London, who led the research.

“That impulse may be culturally ingrained. Richer families have more time and money to afford surplus benefits for their kids like a good diet, helping with homework and time to read to them at night. These benefits are diluted sharply as more children are born.”

Other academic studies have assumed that, while parents generally favour their first-born, this is less pronounced among the rich because they have enough resources to spread around.

In a paper published last week, Lawson and Professor Ruth Mace from UCL examined how much time and attention 14,000 British families gave each of their children. They analysed the effect on offspring by the number of siblings and their parents’ wealth and found a clear “later-born disadvantage”.

There is evidence from elsewhere to back up the idea that the extra care and attention may lead to greater success in later life for older children.

Analysis has found they are, for example, overrepresented among senior executives and surgeons.

Bill Clinton, the former US president, has often been contrasted with Roger, his younger brother, who was jailed for cocaine dealing.

Tamara Mellon, founder of Jimmy Choo shoes, is the oldest of three children, and had particular attention lavished on her by her entrepreneur father, Tommy Yeardye.

In the royal family and, since Norman times, the aristocracy, the system of primogeniture has formalised the practice of favouring the oldest child.

This has enabled families to pass power and wealth down the generations by bequeathing estates intact to the oldest son rather than, as in much of Europe, breaking them up by distributing them evenly among siblings.

For the latest study, Lawson was given access to one of the world’s biggest databases on family dynamics, created by the Avon Longitudinal Study of Parents and Children (Alspac) which enrolled more than 14,000 women who gave birth between April 1991 and December 1992 in the former county of Avon.

Alspac has been following the progress of them and their children since, with studies of the families and their medical records up to three times a year. It has now built up one of the world’s best databases on families and parenting.

Describing the habits of richer families, they said: “Each additional sibling markedly reduces the amount of care that both mother and father give to each child.

“We find clear evidence of a later-born disadvantage with the presence of older siblings linked to a larger deficit in parental care. Strong birth order effects on IQ and health outcomes have also been demonstrated in modern populations consistent with a later-born disadvantage.”

Why, though, should similar effects be weaker in poorer families? The researchers suggest this is because there are so few resources it is harder to give one child much more time, love or possessions than another.

Other researchers have found other effects of birth order. Later-born siblings have been found to be shorter than earlier ones and a Norwegian study found that the eldest child has an IQ averaging three points higher than the second.

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Younger ones can shine

— Older siblings may start off with all the advantages, but this does not stop some of their younger brothers and sisters from surpassing them

— Rowan Atkinson, the star of Mr Bean and Blackadder, has two older brothers. Rodney, the oldest, stood unsuccessfully for leadership of the UK Independence party in 2000

— Dame Judi Dench went into acting inspired by her older brother, Jeffery, a respected character actor. “I might try doing something, like going into the theatre, and then she comes along and goes not one, not two, but three better,” he has said. Another older brother is a doctor

— Bill Gates the Microsoft billionaire and philanthropist, is the middle of three children. His older sister, Kristi Gates Blake, is a former accountant who lives quietly in Washington state. He also has a younger sister, Libby Gates Armintrout

— Being the fifth of six children did not hold back Charles Darwin. His older brother Erasmus shared an interest in plants with the author of On the Origin of Species but “retired” from studying at the age of 26 because his father thought him too frail for a career

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