Melbourne (PTI): Children of older fathers perform less well in intelligence tests during infancy and early childhood, Australian reserchers have found, adding to evidences linking paternal age to neuro-developmental disorders in offspring.

However, children born to older mothers gain higher scores in the same tests, designed to measure the ability to think and reason, memory and concentration, and motor skills, revealed University of Queensland researchers.

The results, they said, were surprising a clear warning to the growing number of men in Western societies who are delaying parenthood until their 40s or older.

The study lead author John McGrath from the Queensland Brain Institute at the university said biological clocks were also ticking for men.

"The results were quite startling as it was thought that the age of the father was less of a concern compared to the age of the mother," McGrath said adding "Now we are getting more evidence of the age of the father being just as important."

The research, published in the medical journal PLoS Medicine on Monday, re-analysed data from one of the largest studies of children in the US, the Collaborative Perinatal Project, Sydney Morning Herald qouted the report on Tuesday.

Over 33,000 children were tested at eight months, four years and seven years on a variety of intelligence tests, and researchers factored in maternal age and socio-economic differences in the study.

The authors said in contrast to their father's age, children of older mothers performed better in intelligence tests, which could be put down to socio-economic factors or because these children experienced a more nurturing home life.

McGrath said scientists suspected that older men were more likely to produce sperm containing an increased number of mutations, and these DNA errors are passed on to offspring.

Unlike women, men remain fertile and continued producing sperm even in old age.

"These mistakes then pile up and increase the risks of problems in the children, and it is possible that these mistakes will carry on into the next generation," he McGrath said.