There is no free will. Sure, we all make decisions every day, but an emerging theme in brain research says that we live under the influence of numerous factors that push us one way or another. Put people in a hot room reeking of rotten garbage and they become more racist and xenophobic. They give more socially conservative responses to questions than they would if the same questions were posed in a comfortable room that smells of roses. Odor and other factors –hormones in particular– modulate nerve impulses in some of the most ancient pathways in the brain. Information in those ancient pathways is unconscious, but those pathways connect with the most modern part of the brain –the cerebral cortex, where we do our thinking. The connection happens through a region in the cortex known as the insula. It happens throughout life, including when you are pregnant. Indeed, pregnancy appears to increase one’s vulnerability to these unconscious influences.
Last year, a fascinating article in The Atlantic summed up research studies relevant to how the biology of pregnancy can affect a budding mother’s outlook on other people. In particular, mothers tend to be more xenophobic, more cautious and fearing of people from of cultures, during the first trimester compared with the remainder of pregnancy. One reason that has been hypothesized involves the vulnerability of an embryo and early fetus to infectious disease. The Atlantic writer cites a big review paper by Tulane University and University of British Columbia researchers giving evidence that the connection involves the immune system.
To give you an idea of how this works, let’s consider a classic and most-feared infectious disease, rubella, sometimes called German measles. Congenital rubella syndrome, resulting from a mother being infected with rubella early in pregnancy, is a very serious problem. A high fraction of such children will go blind, deaf, or suffer from cardiovascular malformations, especially a patent ductus arteriosus (connection between the aorta and pulmonary artery that’s needed during fetal life fails to close after birth) and stenosis (narrowing) of the pulmonary artery. It is a horrible pregnancy outcome, but it is preventable through immunization. That is why your doctor encouraged you to update your rubella vaccine prior to getting pregnant.
But most of human evolution took place prior to the invention of vaccination. Our immune systems defend us best against diseases that are common in the population around us. The immune system is not so good at defending against diseases that it has never seen. That’s rare today, because we live in an age of rapid travel of many people between countries, but consider how European diseases like smallpox killed off Native American people so rapidly, centuries ago. Think from this perspective and you’ll see that there could have been an evolutionary advantage for a pregnant woman to feel an urge to avoid foreigners –even at times when there was no war, and thus no reason to think that foreigners would be hostile. Those who avoided foreigners during the first trimester were less likely to be infected with a new disease that could harm the future child. Through Darwinian selection, this trait was passed on through generations, and may still be with you today. That’s the hypothesis, anyway, and there’s still a lot of research that needs to be done to see if it holds true. If it is true, though, it could mean that keeping yourself as healthy as possible so that you are less fearful of disease may also make you less fearful of those who are different from you.