Sub-par embryos are terminated automatically; embryos improve test performance by exaggerating formerly honest quality signals; new honest indicators arise while old degraded indicators linger

Embryo Selection and Mate Choice: Can ‘Honest Signals’ Be Trusted? Dakota E. McCoy, David Haig. Trends in Ecology & Evolution, January 28 2020. https://doi.org/10.1016/j.tree.2019.12.002

Highlights
.    Mate choice by honest signaling is a classic explanation for elaborate traits in nature. Many researchers have: (i) observed deceptive signaling, and (ii) wondered how honest signals relate to trait elaboration.
.    Honest signaling is analogous to high-stakes testing. Quality is hard to measure directly, so proxies (tests) are used. High-stakes testing causes ‘teaching to the test’ without improving educational outcomes.
.    Embryo choice is another high-stakes test. Mothers select healthy embryos and terminate sub-par embryos automatically. Embryos are selected to pass maternal tests without improving their quality. The resulting arms race causes extreme and elaborate signals during pregnancy.
.    We can better understand elaborate traits in nature if we interpret mate selection, and embryo choice, as a dynamic give-and-take between two parties with conflicting fitness interests.

Abstract: When a measure becomes a target, it often ceases to be a good measure – an effect familiar from the declining usefulness of standardized testing in schools. This economic principle also applies to mate choice and, perhaps surprisingly, pregnancy. Just as females screen potential mates under many metrics, human mothers unconsciously screen embryos for quality. ‘Examinees’ are under intense selection to improve test performance by exaggerating formerly ‘honest’ signals of quality. Examiners must change their screening criteria to maintain useful information (but cannot abandon old criteria unilaterally). By the resulting ‘proxy treadmill’, new honest indicators arise while old degraded indicators linger, resulting in trait elaboration and exaggeration. Hormone signals during pregnancy show extreme evolutionary escalation (akin to elaborate mating displays).