Birgitte Hollegaard:
Using large-scale public health data to explore the evolutionary biology of human pregnancy and child bearing

Date: 15-11-2016    Supervisor: Jacobus J. Boomsma

Medicine has made a giant leap forward over the last century when it comes to the treatment of human disease, but even the most cutting edge 21st century medicine cannot prevent new diseases arising, nor those thought to be extinct developing resistance to pharmaceuticals and returning. Consequently, research has increasingly focused on the underlying causes of disease, shaped by human evolution. Evolutionary medicine is a relatively new field, specifically bridging the gap between conventional medicine and evolutionary biology: Instead of asking how we get sick, we can apply evolutionary hypotheses to unresolved problems in conventional medicine, to ask instead why we get sick. This thesis focuses on pregnancy, generally perceived as a period of harmonious cooperation between a mother and fetus, when in fact the differences in optimal outcome for the genes of the mother, father and fetus can lead to a series of conflicts. Here, I take an evolutionary perspective to investigate why these conflicts exist, and how they are maintained despite the potentially detrimental effect they can have on the health of the mother and child.

The pregnancy induced disease preeclampsia is caused by the mother's blood pressure increasing to a harmful level, but the etiology of the disease has remained unknown. Preeclampsia is detrimental to both the mother and offspring, and should in theory therefore have been removed by natural selection. I looked into evolutionary explanations for this, specifically, whether the paternal genes are able to manipulate maternal blood pressure, thereby increasing resources available to the fetus, and thus benefit its future health. We used the Danish Health Registries to test this hypothesis and as predicted, a fetus exposed to a slightly increased blood pressure had long-term positive health benefits, but if the condition progressed to preeclampsia the health benefits disappeared; this is consistent with evolutionary hypotheses about parental conflicts over resources.

Building upon these results, I further investigated the health of offspring up to 30 years after being exposed to either mild or severe preeclampsia. When I examined the impact from duration of exposure, I found that longer exposure during pregnancy increased the future morbidity risks of the child, even when exposed to only mild preeclampsia.

Finally, I aimed to gain insight into why women who have only sons have a higher risk of morbidity and mortality, compared to women who have only daughters, or children of both genders. This effect has previously been shown in historical data and in this thesis I confirm the results for a contemporary population; then, taking an evolutionary perspective, I discuss possible explanations for this phenomenon. This thesis demonstrates how taking an evolutionary perspective can help us to better understand important aspects of health and medicine that remain opaque, using the specific example of pregnancy-related conditions.