By Jessica D. Ayers
4th year Social Psychology graduate student, Arizona State University
Pregnancy is an exciting time for moms-to-be, but it also comes with challenges as moms experience physiological changes, such as developing food cravings and aversions.
But why do cravings and aversions develop? One theory is that cravings and aversions help moms get the necessary nutrients to the fetus and avoid foods that might hurt the fetus. However, the opposite can be true, where cravings and aversions indicate problems during gestation. To understand which version is happening, we have to look at the genetic conflict happening during pregnancy.
Most of us think our genes make our blueprint as soon as sperm from dad meets egg from mom and then let development take its course. But this isn’t quite true – genes from mom and dad bring different blueprints for how we should develop leading to genetic conflict. Sometimes the designs in the blueprints are similar, but often they are very different. Your genes’ desires are battling it out, working against one another to make your development follow their blueprint. While this might sound like science fiction, genetic conflict is one of the facts of life that shapes how we grow and develop.
One way to think about genetic conflict is as a tug-of-war: Genes from your father are pulling on one end of the rope while genes from your mom are pulling in the other direction. Both sides are pulling on the rope as hard as they can to pull your development towards their blueprint. Your ultimate development ends up being somewhere in the middle. But sometimes things can get out of balance in this battle.
Some pregnancy complications like pre-eclampsia, a complication characterized by high blood pressure, swelling of hands and feet, and protein in mom’s urine, can result from this tug-of-war between maternal and paternal interests. In general, when genes from dad are active the fetus grows slightly larger than when genes from mom are active. Similarly, when genes from dad are active in the fetus, the placenta – an organ genetically identical to the fetus that interacts with mom’s physiology – causes mom to be more resistant to insulin and have higher blood sugar than when genes from mom are active. As mom’s genes inside the fetus try to keep growth and blood sugar under control, dad’s genes fight for more nutrients by increasing mom’s blood pressure via the placenta. This causes mom’s genes to counter and lower blood pressure until dad’s genes respond again in a downward spiral that can lead to complications.
Harvard evolutionary biologist David Haig – who was the first person to apply the framework of genetic conflict to human pregnancy in 1993 – says that escalation of this conflict between mom and dad’s genes is the reason for pre-eclampsia and that we shouldn’t be looking at pregnancy complications as the result of something that is “broken” during pregnancy. Instead, we should be using the framework of genetic conflict to better understand how differing interests between mom and dad’s genes contribute to dysregulation and escalation of conflict during pregnancy.
This is what I am doing now in my graduate work, applying the framework of genetic conflict to predict pregnancy complications from eating behavior during pregnancy. In other words, do mom’s cravings and aversions tell us about the genetic conflict going on in the womb and, in particular, tell us whether there has been an escalation of that conflict (which we would predict to be associated with pregnancy complications). My graduate advisor Athena Aktipis, assistant professor of psychology at Arizona State University, says, “since maternal-fetal conflict influences both physiological and psychological processes, it can influence many aspects of maternal health, from pre-eclampsia to auto-immune disease to eating preferences in pregnancy. We also think it is possible that maternal-fetal conflict may contribute to aspects of postpartum maternal health.” We are still in the early stages of this project, but it is exciting to see that eating behavior does predict certain pregnancy complications in the data we have already collected.
Our preliminary results suggest that we can predict some pregnancy complications such as infections, pre-eclampsia, and gestational diabetes from maternal eating behavior. We also found that more severe pregnancy complications were associated with more problems breastfeeding, and more severe pregnancy complications were associated with a decrease in bonding with the baby both in the short-term and overall. This link between complications and bonding problems is important because postpartum difficulties are associated with early life stress that affects development long term.
If we can reliably predict pregnancy complications based on cravings and aversions early in pregnancy, this would be a major breakthrough since many of these complications are dangerous for both mom and baby but can’t be tested for until late in pregnancy. “If we could understand the mechanisms involved in genetic conflict, we can make better predictions about when genetic conflict can lead to health consequences, especially during pregnancy,” says Amy Boddy, professor of anthropology at the University of California, Santa Barbara and one of our collaborators on the project. She added, “The mother and the baby are not isolated units.”
Indeed, they are not, and by understanding how the conflict between mom’s and dad’s genes inside the developing baby can influence maternal health during pregnancy, we might be able to intervene earlier to protect both maternal and fetal health.
More articles about pregnancy and genetic conflict:
- Why pregnancy is a biological war between mother and baby
- Pregnancy: cooperative paradise or conflict-driven battle between mother and child?
- A Pregnancy Souvenir: Cells That Are Not Your Own
This piece was produced in collaboration with the NPR Scicommers
Peer Edited by Kara McIver
Background image credit: National Cancer Institute