The evolutionary biology of spontaneous abortion in humans

doi:10.1016/S0169-5347(97)01179-8

Trends in Ecology & Evolution

Volume 12, Issue 11, November 1997, Pages 446-450

https://doi.org/10.1016/S0169-5347(97)01179-8 Get rights and content

Abstract

Human mothers an efficient screening system to eliminate genetically abnormal embryos. However, the incidence of certain birth defects — most notably Down's syndrome — rises with maternal age. Conventional eplanations have focused on a rising production of defective zygotes; in contrast, an evolutionary approach suggest a relaxed maternal screen. Relaxed screening potentially explains the rising incidenee of chromosomal abnormalities in live-births, the incidence of normal embryos in spontaneous abortions, and the incidence of spontaneous abortions with maternal age. If true, then restoration of the screen may be possible, reducing the incidence of birth defects.

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Theories of population variation in selection in utero attempt to explain frailty within narrower subgroups. Forbes (1997) offers an evolutionary perspective to the observation that incidence of Down syndrome (trisomy 21) among live births rises with advanced maternal age. He forwarded the relaxed filter hypothesis in which aging nulliparous mothers, nearing the end of their reproductive lifespan, reduce the stringency of their maternal screen against frail or low-quality gestations and thereby allow them to progress to a live birth.
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Low levels of first trimester hCG and low transcription of CGB genes indicate maternal susceptibility to miscarriage, chromosomal abnormalities of the fetus, or ectopic pregnancy (Rull & Laan, 2005; Stenman, Tiitinen, Alfthan, & Valmu, 2006). Human mothers use selective spontaneous abortion as a mechanism for quality control (Forbes, 1997, 2005). Recent work by Catalano and colleagues shows that frail males are culled during periods of environmental stress (Catalano, Currier, & Steinsaltz, 2014; Catalano, Margerison-Zilko, et al., 2012, Catalano, Saxton, et al., 2012; see also Boklage, 1990; Wells, 2000) and the link between hCG level and embryo fitness is clear and direct.
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Much literature argues that natural selection conserves mechanisms that allow women to spontaneously abort gestations least likely to yield fit offspring (Baird, 2009; Forbes, 1997; Møller, 1997; Stearns, 1987; Trivers & Willard, 1973; Wells, 2000). This “selection in utero” implies that somewhere in the biology of pregnant women is a means to estimate the ratio of likely grandchildren (a result of fit offspring) to maternal investment required to sustain offspring from gestation through reproductive age (Baird, 2009; Forbes, 1997; Møller, 1997; Stearns, 1987; Wells, 2000). Relatively low ratios presumably put a gestation at greater risk of spontaneous abortion (Wells, 2000).
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Trends in Ecology & Evolution

PerspectiveThe evolutionary biology of spontaneous abortion in humans

Abstract

Trends Ecol. Evol.

Lancet

Ethol. Sociobiol.

Lancet

Int. J. Gyn. Obst.

Hypotheses for the production of excess zygotes: models of bet-hedging and selective abortion

Evolution

On the evolution of human brood size

Evolution

Occult pregnancy as afactor in unexplained fertility

J. Reprod. Med.

Sonar evidence of early pregnancy failure inpatients with twin pregnancies

Brit. J. Obstet. Gynecol.

Epidemiology of chromosomal anomalies in spontaneous abortion: prevalence, manifestation and determinants

Why are twins so rare in Homo sapiens?

Am. Nat.

Chiasma frequency and maternal age in mammals

Nature

Oocyte selection: a new model for maternal age-dependence of Down syndrome

Human Genetics

An experimental approach to the analysis of mechanisms of meiotic nondisjunction and anaphase lagging in primary oocytes

Cytogenet. Cell Genet.

A chiasmahormonal hypothesis relating to Down's syndrome and maternal age

Nature

Down syndrome, paternal age, maternal age and birth order

Ann. Hum. Genet.

Maternal-age effect in aneuploidy: does altered embryonic selection play a role?

Am. J. Hum. Genet.

Evidence that altered embryonic selection contributes to maternalage effect as aneuploidy; A spurious conclusion attributable to pooling of heterogeneous data?

Am. J. Hum. Genet.

Down syndrome rates andrelaxed selection at older maternal ages

Am. J. Hum. Genet.

Perspective
The evolutionary biology of spontaneous abortion in humans