Most women would find it hard to believe that morning sickness -- vomiting and nausea during pregnancy -- is a good thing, but the evidence is growing that it helps protect the mother and her baby.

In a paper in the Quarterly Review of Biology, Samuel Flaxman and Paul Sherman of the Department of Neurobiology and Behavior at Cornell University have reviewed a wealth of evidence from medical, psychological and anthropological studies. They conclude that morning sickness is adaptive. That is, it has a selective function: to prevent women from ingesting foods which might be dangerous to themselves or their embryos.

Around two-thirds of women suffer from morning sickness, usually during the first trimester (the first 13 weeks) of pregnancy. Despite its name it can occur throughout the day and is more accurately termed nausea and vomiting during pregnancy (NVP).