Evolutionary Perspectives on Pregnancy by Avise John

Evolutionary Perspectives on Pregnancy by Avise John

Author:Avise, John
Language: eng
Format: epub
Tags: SCI027000, Science/Life Sciences/Evolution, SCI056000, Science/Life Sciences/Anatomy & Physiology (see also Life Sciences/Human Anatomy & Physiology)
Publisher: Columbia University Press
Published: 2013-01-07T16:00:00+00:00


Factoid: Did you know? Gestational diabetes occurs in about 4% of human pregnancies, meaning that approximately 135,000 pregnant women per year experience this condition in the United States alone.

Factoid: Did you know? Preeclampsia affects about 5% of human pregnancies and is a leading cause of perinatal mortality, preterm birth, and maternal morbidity (Aubuchon et al. 2011).

A third possible example of maternal-fetal conflict involves human chorionic gonadotropin (hGH), a hormone produced by the conceptus that enters the mother’s bloodstream and impels her body to retain (rather than abort) the fetus (Neese and Williams 1994). Without such fetal manipulation of maternal physiology, mothers otherwise seem to have evolved surveillance mechanisms to recognize and reject defective fetuses. Such maternal screening mechanisms make evolutionary sense because a female can increase her lifelong genetic fitness by detecting and aborting any defective conceptus early in a pregnancy (and then perhaps starting over), even if this comes at the increased risk of occasionally killing a normal embryo. By secreting high levels of hGH, the fetus in effect is trying to prove its good health to a mother who has evolved physiological mechanisms that make her suspicious of such biochemical manipulations by the embryo.

Sometimes maternal-fetal gamesmanship during evolution can play out in ways that are subtler or far less disastrous for a pregnancy than are gestational diabetes, preeclampsia, or spontaneous abortion. An interesting case in point is the common phenomenon of “morning sickness” or “pregnancy sickness,” wherein expectant mothers become easily nauseated and show strong aversions to or cravings for specific foods. One proximate explanation is that high levels of hGH contribute to this sensitivity, in which case morning sickness might be viewed as an unhappy evolutionary by-product of the genetic conflict between mother and embryo (Haig 1993; Forbes 2002). Another evolutionary interpretation is perhaps more conventional (Hook 1978): that mothers have evolved physiologies that confer sensitivities to any environmental contaminants that might compromise an otherwise successful pregnancy (Profet 1988, 1992; Sherman and Flaxman 2001). According to this view, morning sickness could be part of an adaptive response that discourages the ingestion of toxins and promotes the ingestion of healthy foods during a pregnancy. Under either explanation, pregnancy sickness is not an inexplicable pathological condition but a syndrome that emerged in response to selective pressures in the stressful biological environments in which humans evolved.



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