Parenting: Louise Holden looks at how grannies are providing much more than babysitting.

Have you ever wondered why the human female lives for so many years beyond fertility? In most other species, females continue to reproduce until they die, but human females live for 20 to 40 years beyond the menopause. Only in elephants and some whale species is the same phenomenon observed.

Researchers in Finland believe they have cracked it. The granny has finally found her place in evolutionary theory. A study looking at the lives of 2,800 women in Finland over two centuries has concluded that grandmothers exist because of an evolutionary necessity to provide the support that allows younger generations to produce more offspring. Without an older woman to look out for us, we produce fewer, sicker children, the study found.

The researchers examined the reproductive patterns of women in Finland and Canada. They discovered that long-living grandparents had an influence on their family's reproductive success. Women were more likely to have children at a young age if their own mothers were still alive, and the grandchildren were more likely to survive, the study found.

Children who reached the age of two were more likely to reach the age of five if they had a living grandmother. Young grannies had a particularly beneficial impact - around 12 per cent more grandchildren survived to adulthood when their grandmother was under 60, though the benefit was reduced to 3 per cent if the grandmother was older.

What does this mean for the menopausal woman? Has she her children's fertility to thank for night sweats and HRT? The researchers are unclear as to whether the menopause actually evolved to free older women up to be grannies.

Writing in the science magazine Nature, the researchers, led by Dr Mirkka Lahdenpera, said: "Although grandmother effects alone are suggested to be insufficient to account for the evolution of the menopause, our results suggest that they can be sufficient to account for the evolution of the substantially prolonged post-reproductive life-span observed in humans."

Grannies (and granddads) are shouldering more than their fair share of childcare responsibilities in Ireland, helping their daughters and sons to work, buy property and produce more children. New parents take note - stick close to your mums. It's an evolutionary necessity.

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Raising Dust

Parents of asthma sufferers should take precautions when doing housework with their wheezy children around.

According to a report in the March edition of Environmental Science & Technology, ordinary household activities, from dusting to dancing, can increase your exposure to particulate pollution, a new study has found.

Particles can accumulate in the respiratory system and aggravate health problems such as asthma. Homes are filled with these particles, which often come from outdoors, cooking, smoking, heating equipment and, according to the study, dust kicked up from human activities.

The results could help people make a variety of decisions about living in their homes. "One study estimates that about two-thirds of house dust is tracked in from outdoors," a spokesperson said. "Therefore, leaving shoes at the door can make a big difference in reducing the particle reservoir on the floor."

She also recommends leaving windows open while cleaning to increase ventilation; limiting the use of toxic household products, such as pesticides; and installing non-carpet flooring.

Drinking in pregnancy

Newborns whose mothers drank alcohol heavily during pregnancy had damage to the nerves in the arms and legs, according to a study by researchers at the US National Institute of Child Health and Human Development.

The damage was still present when the children were re-examined at one year of age.

The study is the first to look at whether exposure to alcohol before birth affects the developing peripheral nervous system rather than the brain or spinal cord. The study appears in the March issue of the Journal of Paediatrics.

"Infants born to mothers who drink heavily during pregnancy are known to be at risk for mental retardation and birth defects," said Dr Duane Alexander. "This is the first study to show that these infants may suffer peripheral nerve damage as well."