The Elements of Evolution (43-8) Cryptic Coloration | Eyelashes

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It is extremely common that animals are cryptically colored, thereby blending in with their surroundings. If hypothesized natural selection via random mutation were at work, such optimization would not be so ubiquitous. In that case, poorly colored animals would regularly appear. Instead, such ill-adapted mutations are quite rare: typi-cally, symptomatic of general developmental deficiencies

Eyelashes are found on a wide variety of mammals. They are always about 1/3rd as long as the eye is wide. This allometric proportion is the ideal length for divert-ing airflow around the eye, and thereby minimizing evaporation.