Well, I obviously don't have any personal experience
but I did learn a bit about morning sickness in psych class. Moms, correct me or back me up as appropriate.
We were taught that morning sickness and food aversions are there to prevent birth defects. There are some foods that are more likely to cause defects in a developing baby. Mostly plants. The baby is in the most danger during early development (i.e. the first trimester). So, morning sickness is a way to prevent expectant moms from taking in toxins which would endanger the baby. The sickness prevents them from eating too much in general (the less you have, the less likely you are to take in something dangerous), and the food aversions are to the most dangerous things. Salad was given to us as an example of one of the most common food aversions. It turns out that certain chemicals common in plant leaves can be very dangerous for a developing fetus.
After the first trimester or so, the danger of defects is less. Keeping the baby fed so it can grow and develop is more important. So, morning sickness goes away, replaced with a drive to eat more.
Obviously, there's a lot of variation from mom to mom. Everyone feels it differently. That's the general theory, though, as taught to me by my Psych prof (who is also male). Take it for what it's worth.
Paul
