Cover image

Herbivorous mammals in relaxed postures are shown in the foreground. In the distance, nonherbivorous mammals are shown in grayscale. The lack of color in the nonherbivores represents constrained molecular evolution, whereas the color in the herbivores represents a relaxation of evolutionary constraint as mammalian lineages become more herbivorous. A colorful DNA helix emerges from behind the herbivores, surrounded by plant-based foodstuffs and depictions of the liver and kidneys. In this issue, it is reported that genes associated with liver and kidney functions experience reduced evolutionary constraint and functional importance as increasingly herbivorous diets evolved across Mammalia. (Photo collage created by Matthew D. Pollard in Adobe Photoshop, using public domain images from Wikimedia Commons and images generated by DALL-E 3. [For details, see Pollard et al., pp. 2176–2189.])