Classically explained as an adaptation for camouflage, countershading describes the color pattern common among animals and is characterized by darker pigmentation on the side of the body that is most strongly illuminated.
Countershading is a color pattern that is observed in a diversity of taxa, across contrasting environments (Rowland 2009), and across ecological time (Smithwick et al. 2017). There are a number of reasons that countershading might evolve, including thermoregulation, protection against UV radiation, and defense against abrasion (Rowland 2009). The most researched hypothesis for the existence of countershading is that it enhances visual camouflage.
The History of Countershading
The English naturalist Edward Bagnall Poulton and American artist Abbott Thayer independently proposed that the function of countershading is to enhance camouflage (Rowland 2009)....
- Smithwick, F. M., Nicholls, R., Cuthill, I. C., & Vinther, J. (2017). Countershading and stripes in the Theropod Dinosaur Sinosauropteryx reveal heterogeneous habitats in the Early Cretaceous Jehol Biota. Current Biology. https://doi.org/10.1016/j.cub.2017.09.032
- Vinther, J., Nicholls, R., Lautenschlager, S., Pittman, M., Kaye, T. G., Rayfield, E., …, & Cuthill, I. C. (2016). 3D camouflage in an Ornithischian Dinosaur. Current Biology, 26(18), 2456–2462. https://doi.org/10.1016/j.cub.2016.06.065