Older brothers may lower fertility levels

New research suggests that having an older brother may lower an individual's fertility.

A study carried out by researchers at the University of Sheffield has found that for both men and women, those whose mothers had previously had a son, had fewer children than those whose mothers had given birth to a daughter.

It was also found that those with an older sister had 12 per cent more children.

"There is evidence from many species that sons are more costly for mothers to give birth to and care for than daughters," said lead researcher Ian Rickard.

"It now appears that after producing a son, a mother may be less able to invest in her next child.

"This reduced investment may compromise the early development of the body's physiological systems, including those important for reproduction."

In a separate study produced by the University of Sheffield earlier this year, researchers found that women were 25 per cent less likely to have children if they had a male twin.

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