Pregnancy Sickness Could Be Beneficial for Your Growing Baby

The evolutionary roots of morning sickness

Posted Mar 19, 2011


One of the grossly misunderstood epistemological tenets of evolutionary theory is the distinction between proximate and ultimate explanations. One cannot appreciate the explanatory power of evolution without having a grasp of this crucial issue. Proximate explanations address the how and what of a phenomenon. How does testosterone (T) lead to intrasexual aggression? How is T produced in a man's body? What are some environmental triggers that might cause a man's T to fluctuate? What are the physical signs of endemic low T? All of the latter questions and countless others are examples of proximate questions dealing with T. Much of science has operated and will continue to operate at the proximate level.

Evolutionary theory adds another explanatory layer for a given phenomenon. Ultimate explanations tackle the Darwinian why. In other words, what is the adaptive genesis (if any) of a given behavior, cognition, emotion, or morphological trait? Returning to the T example, an ultimate explanation might seek to understand the selective forces that would have yielded much higher T levels in men than in women. Hence, it is not that ultimate explanations are superior to proximate ones (although some individuals mistakenly confuse 'ultimate' as meaning 'superior'). Rather, as I have repeatedly taken great care to explain to marketing and consumer scholars, both explanatory levels are needed to fully understand a phenomenon that involves biological organisms. Since humans are biological creatures (a highly contentious statement to many social scientists), to fully understand Homo sapiens requires that we ask questions at both the proximate and ultimate levels.

My work for much of the past fifteen years has been to introduce ultimate-based theorizing within the field of consumer behavior (see my academic and trade books here and here). One cannot imagine the level of hostility that I have garnered from many marketing scholars in response to my Darwinizing efforts albeit the winds are beginning to change. Patience is indeed a virtue when it comes to the auto-corrective capacities of science.

Whenever I discuss the distinction between proximate versus ultimate explanations, I often use pregnancy sickness as the illustrative example. There are an endless number of proximate questions that can be posed regarding pregnancy sickness, many of which your OB/GYN is intimately knowledgeable about. Less known is the ultimate explanation of pregnancy sickness. Recall that this would require our asking the following question: why would women have evolved this physiologically predictable reality? In other words, pregnancy sickness might be an adaptation to what in particular? It turns out that pregnancy sickness coincides with organogenesis, namely the gestational period when the baby's organs are forming. During this crucial time frame, it is terribly important that the fetus not be exposed to any environmental injuries, which typically come in the form of food pathogens (and other teratogens). To the extent that such a reality would have been quite likely in our evolutionary past, it would be adaptive for pregnant women to evolve food aversions and cravings that cater to this threat. Furthermore, it would make evolutionary sense that a physiological mechanism would evolve that expels such pathogens in the event that a pregnant woman ingests these.

Margie Profet gained worldwide fame for having offered this evolutionary account of pregnancy sickness. Since her seminal 1992 chapter in The Adapted Mind: Evolutionary Psychology and the Generation of Culture, numerous scientists have validated this Darwinian-based hypothesis (cf. Flaxman & Sherman, 2000; Sherman & Flaxman, 2002; Pepper & Roberts, 2006) by investigating the link between the extent to which women experience the symptoms of pregnancy sickness and outcome metrics (e.g., miscarriage rates, embryo quality). The findings suggest that it is beneficial for women to experience pregnancy sickness...which is exactly what your physician will seek to maladaptively shut off!

Not only does this example offer a compelling demonstration of the benefits of tackling problems at both the proximate and ultimate levels but also it shatters the infinitely ignorant attacks levied against evolutionary theory regarding its supposed capacity to engage in unfalsifiable fanciful just-so story telling.

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