Morning sickness is pregnancy 'wellness insurance'

Jun 26, 2008

Morning sickness. It's the bane of many of a pregnancy. And many a future mother wonders at the apparently unnecessary suffering.


But, it turns out, there's meaning to the misery. Two evolutionary biologists report that morning sickness protects both the pregnant woman and the developing embryo just when the fetus is most vulnerable.

After testing the two dominant theories (one adaptive and the other non-adaptive) for why two-thirds of women around the world -- but seemingly no other mammals -- experience nausea and vomiting in pregnancy, only one holds water, says Paul Sherman, Cornell professor of neurobiology and behavior and a Weiss Presidential Fellow.

"Our study, which tested theories and predictions about the nature of parent-offspring conflict in human pregnancy, shows that nausea and vomiting in pregnancy is beneficial by expelling such foods as meat and strong-tasting vegetables that historically and still may contain harmful toxins and microorganisms that could potentially sicken the woman and damage her fetus just when its organs are developing and are most vulnerable to chemicals," said Sherman, who is an expert in Darwinian medicine -- viewing diseases from an evolutionary perspective.

His study, conducted with University of Colorado evolutionary behaviorist Samuel M. Flaxman '98, Ph.D. '05, who worked as a postdoctoral researcher at Cornell from 2005 to 2007, is published in the July issue of The American Naturalist.

Other evidence that the theory that morning sickness is protective and beneficial, he said, includes:

-- The nausea and vomiting declines after 18 weeks of pregnancy, as the fetus becomes less vulnerable to the effects of chemical disruptions.
-- Women with the most severe morning sickness have lower rates of spontaneous abortion than other pregnant women.
-- Historically, meat and strong-tasting vegetables were likely to contain parasites, pathogens and plant toxins; these foods tend to reliably trigger morning sickness symptoms across cultures. Alcohol and cigarette smoke, which also can harm the fetus while organs are forming, also trigger the nausea.
Societies that consume more meats, strong-tasting vegetables and alcohol have higher rates of morning sickness than societies whose staples are bland plant products.
-- Only humans experience morning sickness, as far as is known, because, the researchers suggest, of their "extraordinary broad diet," compared with other primates and mammals.

If the alternative theory that morning sickness is a non-adaptive outcome of an evolutionary tug-of-war between the mother and fetus for resources were correct, then the nausea should peak in the final trimester, when the fetus requires more nutrients and blood than at any other time. But it doesn't. Neither does it occur with every pregnancy. If morning sickness were the result of the fetus signaling its viability to the mother, then all humans and other mammals should experience it.

"All this leads us to suggest that morning sickness is a misnomer," Sherman said. "It doesn't occur just in the morning, and it's not an illness. It can occur any time of day and it appears to be beneficial -- we could call it a form of evolutionary wellness insurance."

The current study builds on a 2000 paper published in the Quarterly Review of Biology in which Sherman and Flaxman studied the outcomes of thousands of pregnancies. In that study, they noted, for example, that in the seven traditional societies that had virtually no morning sickness, the diets were based on bland, plant-based foods rather than meats and strong-tasting vegetables.


Source: Cornell University

Explore further: Japan orders air bag maker to conduct probe

add to favorites email to friend print save as pdf

Related Stories

Senators get no clear answers on air bag safety

1 hour ago

There were apologies and long-winded explanations, but after nearly four hours of testimony about exploding Takata air bags, senators never got a clear answer to the question most people have: whether or ...

Nicaragua: Studies say canal impact to be minimal

1 hour ago

Officials said Thursday that studies have determined a $40 billion inter-oceanic canal across Nicaragua will have minimal impact on the environment and society, and construction is to begin next month.

Former Brown dean whose group won Nobel Prize dies

2 hours ago

David Greer, a doctor who co-founded a group that won the 1985 Nobel Peace Prize for working to prevent nuclear war and who helped transform the medical school at Brown University, has died. He was 89.

Recommended for you

Japan orders air bag maker to conduct probe

Nov 21, 2014

Japan's transport ministry said Friday it has ordered air bag maker Takata to conduct an internal investigation after cases of its air bags exploding triggered safety concerns in the United States and other countries.

Senators get no clear answers on air bag safety

Nov 20, 2014

There were apologies and long-winded explanations, but after nearly four hours of testimony about exploding air bags, senators never got a clear answer to the question most people have: whether or not their ...

Winter-like temps can reduce tire pressure

Nov 19, 2014

The polar plunge that has chilled much of the nation does more than bring out ice scrapers and antifreeze. It can trigger vehicles' tire pressure monitoring systems overnight, sending nervous drivers to dealers ...

US: Gov't aircraft regulations apply to drones (Update)

Nov 18, 2014

The U.S. government has the power to hold drone operators accountable when they operate the remote-control aircraft recklessly, a federal safety board ruled Tuesday in a setback to small drone operators chafing ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.