Morning sickness is currently understood as an evolved trait that
protects the fetus against toxins ingested by the mother. Many
plants contain chemical toxins that serve as a deterrent to being eaten. Adult
humans, like other animals, have defenses against plant toxins, including
extensive arrays of detoxification enzymes manufactured by the liver and the surface tissues of various other organs. In the fetus, these defenses are not yet fully
developed, and even small doses of plant toxins that have negligible effects on
the adult can be harmful or lethal to the embryo.
Pregnancy sickness causes women to experience nausea when exposed to the smell
or taste of foods that are likely to contain toxins injurious to the fetus, even
though they may be harmless to her.
There is considerable evidence in support of this theory, including:
Morning sickness is very common among pregnant women, which argues in favor of it being a functional adaptation and against the idea that it is a pathology.
Fetal vulnerability to toxins peaks at around 3 months, which is also the time of peak
susceptibility to morning sickness.
There is a good correlation between toxin concentrations in foods, and the tastes and odors that cause revulsion. Women who have no morning sickness are more likely to miscarry or to bear children with birth defects.
In addition to protecting the fetus, morning sickness may also protect the mother.
Pregnant women's immune systems are suppressed during pregnancy, presumably to reduce the chances of rejecting tissues of their own offspring.Because
of this, animal products containing parasites and harmful bacteria
can be especially dangerous to pregnant women. There is evidence that morning
sickness is often triggered by animal products including meat and fish.
If morning sickness is a defense mechanism against the ingestion of toxins, the
prescribing of anti-nausea medication to pregnant women may have the undesired side effect of causing birth defects or miscarriages by encouraging harmful
On the other hand, many domestic vegetables have been purposely bred to have lower levels of toxins than in the distant past, and so the level of threat to the embryo may not be as high as it was when the defense mechanism first evolved.
source frm here: http://en.wikipedia.org/wiki/Morning_sickness
Wednesday, April 7, 2010
Morning sickness as a defense mechanism
The article that can motivate me. *Perhaps*