Having a big brother 'cuts your chances of children'

By Daily Mail Reporter

An elder sibling can have a profound effect on your future life

Whether you idolise or resent him, there's no doubt a big brother can really shape your childhood.

But it seems an elder sibling's influence can have a much more profound effect in later life.

Researchers believe he can affect the fertility of a younger brother or sister - potentially reducing their chance of having a family of their own.

It is thought the phenomenon has its roots in the womb - and that the physical cost of carrying a boy may take so much out of a woman that the health of her next child suffers.

Sheffield University researchers made the link after looking at birth, marriage and death records of three generations in pre-industrial Finland.

Although the effects are small, their study clearly showed that having an older brother cut a sibling's chances of parenthood.

Those with an older sister had a 67 per cent chance of having children. Having an older brother cut

the odds to 62 per cent. Men and women with an older brother also had children later in life and had bigger gaps between births, the journal Evolution and Human Behaviour reports.

The researchers said it was significant that both men and women were affected by the presence of a big brother.

This meant the phenomenon had a biological basis and couldn't simply be explained away by cultural aspects - for instance, the eldest son being favoured over younger brothers as he stood to inherit the family business.

'The fact that men and women have a similarly reduced probability of reproducing when their elder sibling was male, suggests that the cost of being born after an elder brother may have consequences spread over a variety of physiological systems, affecting overall adult quality of both men and women,' the researchers wrote.

A previous study has shown that boys and girls with older brothers tend to be shorter as adults than those with older sisters.

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