BY FAZALE RANA – FEBRUARY 15, 2017
Somewhere between 50% to 70% of women experience morning sickness—nausea, vomiting, and disgust toward certain foods—beginning near the onset of their pregnancies, and continuing for 2 to 3 months into the second trimester.
Interestingly, no other mammal experiences morning sickness. It is a uniquely human trait. This has prompted anthropologists and biomedical scientists to ask, why does morning sickness only occur in humans?
What Causes Morning Sickness?
As Christians, it might be tempting to view morning sickness as part of the curse—the increased pain in childbirth—described in Genesis 3:16–17.
Many anthropologists think that it is an epiphenomenon—a nonfunctional byproduct of humanity’s evolutionary origin. These scientists argue that morning sickness results from the genetic incompatibility between the mother and fetus that leads to a conflict for resources, causing the mother to become ill.
But, in recent years, scientists have identified another explanation for morning sickness, dubbed the prophylaxis hypothesis. They view nausea, vomiting, and disgust toward certain foods as a protective mechanism that keeps both mother and fetus healthy during the initial critical phase of embryonic development.
Recent work provides new support for this hypothesis,1 and, along with it, gives added insight to the biblical idea that as human beings we are fearfully and wonderfully made (Psalm 139:14). Support for the prophylaxis hypothesis also has pro-life implications.
What Is the Purpose of Morning Sickness?
The prophylaxis hypothesis gains support from several observations. First, there are correlations between morning sickness and both reduced incidences of miscarriages and elevated birth weights.
As it turns out, only certain foods trigger nausea and vomiting and serve as the objects of disgust during the first trimester of pregnancy: namely, meats, poultry, eggs, strongly flavored vegetables, and some fruit. These foods are the most likely to harbor pathogens and dietary toxins that can interfere with embryological development (teratogens). Along these lines, it is interesting that the incidence of morning sickness varies from culture to culture, most likely because of dietary differences.
The timing of morning sickness also supports the prophylaxis hypothesis. During the first trimester, the mother’s immune system is suppressed. The genetic differences between mother and fetus makes this suppression necessary. Because the fetus is only 50% genetically identical to the mother, her body treats the fetus as foreign and would otherwise attack it, if it wasn’t for the suppression of her immune system.
Immunosuppression is maximal during the first trimester, leaving both the mother and fetus vulnerable to infection. By the second trimester, the mother’s immunosuppression becomes localized to the interface between the mother and fetus. It is during this time that the developing child’s immune system begins to form. The fetus also enjoys protection from the mother’s antibodies that are transferred to the fetus via the placenta.
The first trimester is also critical because this is when organ development begins in the fetus. At this juncture in development, the fetus is highly vulnerable to infectious agents and reproductive toxins found in fruits and vegetables.
There is also another role that morning sickness and disgust toward certain foods play in the early stages of pregnancy: calorie restriction for the mother. It is counterintuitive, but limiting the caloric intake benefits the pregnancy by inhibiting tissue synthesis in the mother. When calories are few, anabolic pathways shut down. This allows nutrients to be devoted to placental formation.
Why Does Morning Sickness Only Occur in Humans?
Researchers think that morning sickness in humans stems from our wide-ranging diet. Most mammals have highly specialized diets. Because of this, their immune systems can readily target the pathogens most likely to be found in the foods they eat. They can also make use of specialized enzymes to detoxify the teratogens most likely to be found in the foods they eat. This type of specialized protection isn’t feasible in humans, in fact, it might not even be possible at all, because our diets are so wide-ranging—varying from region to region around the world. Unlike most mammal species, humans literally occupy every corner of the planet. And this capability requires us to eat all sorts of foods. Given our highly varied diet, the most efficient and effective way to protect the mother and fetus during the first trimester of pregnancy is through nausea, vomiting, and disgust toward potentially harmful foods—unpleasant as these experiences might be.
Morning Sickness as Evidence for the Christian Faith
Though some biologists have argued that morning sickness is an epiphenomenon that emerged as the byproduct of human evolution, the data indicates otherwise. Morning sickness and disgust toward certain foods plays a critical function in an healthy pregnancy by protecting both the mother and the developing child. As a Christian, I see morning sickness as one more elegantly designed facet of human pregnancy.
I also see it as affirming key passages of Scripture. Instead of seeing morning sickness as support for Genesis 3:16–17, I view it as deepening the meaning of passages in Psalm 139describing each of us as being fearfully and wonderfully made. This latest insight about the benefit of morning sickness also expands my perspective of the idea from Psalm 139 that God has knit each of us together in our mother’s womb.
I also see this insight relating to the command God gave us in Genesis 1 to multiply and fill the earth. To do so would require that we would be able to thrive in a wide range of habitats, demanding that we are capable of consuming a highly varied diet. And of course, this is where morning sickness plays a vital role. For humans to increase in number, while we fill the world, requires a prophylactic mechanism (such as morning sickness) to ensure healthy pregnancies.
On a side note: The prophylaxis hypothesis also points to human exceptionalism. In contrast to our the highly varied diets, Neanderthals consumed a much more limited range of food. In fact, these differences in dietary practices likely reflect differences in the cognitive capacities of modern humans and Neanderthals. It is no accident that Neanderthals had a limited biogeographical distribution, confined to Europe, Western Asia, and the Middle East. In fact, Neanderthals’ limited diet may well have contributed to their extinction.
This work also has implications for the pro-life debate. I have often heard pro-choice advocates argue that abortion is not murder because the fetus is like a tumor. However, the latest insights into morning sickness undermine this position. This argument would gain validity if morning sickness was, indeed, an epiphenomenon, resulting from a tug-of-war between mother and fetus. But the data says otherwise. Even though the fetus is genetically distinct from the mother, the mother’s body is designed to do everything it can to protect the fetus, including develop morning sickness and disgust toward potentially harmful foods.
Though this latest understanding about morning sickness may make evolutionary biologists and pro-choice advocates sick, it spews forth new evidence for design. (Sorry, I couldn’t resist.)
“What Are the Odds of You Being You?” by Matthew McClure (article)
“Placenta Optimization Shows Creator’s Handiwork” by Fazale Rana (article)
“Curvaceous Anatomy of Female Spine Reveals Ingenious Obstetric Design” by Virgil Robertson (article)
“Does the Childbirth Process Represent Clumsy Evolution or Good Engineering?” by Fazale Rana (article)
“The Female Brain: Pregnant with Design” by Fazale Rana (article)
“Dietary Differences Separate Humans from Neanderthals” by Fazale Rana (article)
- Rachel R. Huxley, “Nausea and Vomiting in Early Pregnancy: Its Role in Placental Development,” Obstetrics and Gynecology 95 (May 2000): 779–82, doi:10.1016/S0029-7844(99)00662-6; Daniel M. T. Fessler, Serena J. Eng, and C. David Navarrete, “Elevated Disgust Sensitivity in the First Trimester of Pregnancy: Evidence Supporting the Compensatory Prophylaxis Hypothesis,” Evolution and Human Behavior 26 (July 2005): 344–51, doi:10.1016/j.evolhumbehav.2004.12.001; Samuel M. Flaxman and Paul W. Sherman, “Morning Sickness: Adaptive Cause or Nonadaptive Consequence of Embryo Viability?” The American Naturalist 172 (July 2008): 54–62, doi:10.1086/588081.