Real estate with ocean views, stunning mountain vistas, and wide-open green spaces sell at premium prices because humans find those settings pleasing [1-5]. Certain color combinations in fashion—such as brown and forest green—blend harmoniously, while others, such as hot pink and orange, clash. And our eyes like certain proportions in visual objects (like buildings and human faces) but not others.

These “facts" of visual aesthetics are so well established and obvious that we don’t stop to question them. But here we will, asking, “Exactly why is it that our eyes like what they like?”

As with other dimensions of everyday experience, what we find aesthetically pleasing is not random but stems from our evolutionary history. Just as our innate preference for sweet, calorie-rich food helped our ancestors survive in environments where food was scarce, our preferences for certain visual stimuli reflect the survival imperatives that confronted our ancestors.

Let’s start with an easy one: toxic substances, such as those in rotting meat, tainted water, or feces. Although our noses are the primary defenders against such threats, our eyes also play a role. Rotting meat, moldy bread, and dirty water usually have a distinct, “ugly” look. According to ecological valence theory [6, 7], we generally prefer colors, such as green, that are associated with non-toxic substances and dislike those, such as brown, that are associated with objectionable substances. Similarly, color combinations that occur in welcoming environments—such as sky blue and light brown tree bark in forests—"match,” whereas color combinations that do not occur naturally “clash.” The color pair below on the left, coral and turquoise, evokes the........

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