If you're pregnant and kneeling over the toilet every morning, sometimes late into the afternoon as well, you may think this is a pretty terrible situation. What good could possibly come of you puking your guts out every morning?

Well, some evolutionary biologists believe that morning sickness is, in fact, a good thing. They've studied thousands of pregnancies, successful and unsuccessful, and they've discovered that morning sickness or NVP, nausea and vomiting in pregnancy, seems to be an evolved defense against two potential problems--one, food-borne illness in both the mother and the fetus and two, congenital defects resulting from harmful chemicals in certain foods.

Though not so threatening to fully developed bodies, these chemicals can deform embryonic organs in the early stages of their development. In fact, morning sickness usually peaks between the sixth to eighteenth weeks of pregnancy, the period in embryonic development when the process of organ formation is most susceptible to disruption by chemical toxins.

Not only is there a correlation between morning sickness and this particularly sensitive phase of development, but there is also a correlation between this phase and pregnant women's aversions to certain foods. Many pregnant women experience aversions to meat, caffeinated beverages, and strong-tasting vegetables--the very foods that are thought to contain chemicals potentially harmful to the embryo.

Though most doctors do advise against consuming caffeine during pregnancy, they don't prescribe that you militantly cut all these foods out of your diet. Nor should you worry if you do not experience morning sickness. Mostly, doctors say to listen to your own body.