Morning sickness could be rather annoying for most pregnant women, but it may in fact have the role of protecting the embryo. According to doctors, morning sickness is the sign of a healthy pregnancy, although it's not yet known if it leads to a successful one or not. Alternatively, it could be the effect of the pregnant woman and the embryo fighting over body resources.

Samuel Flaxman, evolutionary biologist at the University of Colorado, says that morning sickness is not just the byproduct of a healthy pregnancy. If it was, then all pregnant women should experience it, which is hardly the case. Only two thirds of pregnant women have morning sickness and the other third usually carry their pregnancy to term without any problems. Additionally, other mammals should also have morning sickness if this were a byproduct of resource conflicts between the mother and the embryo or fetus.

However, morning sickness is induced by certain circumstances, such as the sight, smell and taste of meats and vegetables known to carry foodborne microbes and birth-defect-inducing chemicals, or alcohol and cigarette smoke. This means that morning sickness is actually a defense mechanism serving both the mother and the embryo. It is usually experienced between week six and eighteen of pregnancy, when the organism is mostly susceptible to chemical imbalances.

It is basically a result of the human's broad diet. While other mammals are protected against dangerous toxins by a range of molecules, humans have adapted and learned how to keep their distance from dangerous compounds.

"To say that morning sickness is uncomfortable is a real understatement, and a lot of people are looking at ways to deal with it. But if nausea and vomiting truly serve a useful function, then one has to look more carefully at strategies for dealing with these symptoms", Flaxman said.

Still, very little is known about how morning sickness works and about its nature, in spite of decades of research. "We're really interested in a more exhaustive analysis to see if morning sickness really does only occur in human beings, or whether there are other animals out there", Flaxman said.