Emotional Design by Donald A. Norman

to receive powerful emotional signals from the environment that get interpreted automatically at the visceral level. This is where the lists of features in chapter 1 came from. Thus, the colorful plumage on male
birds was selectively enhanced through the evolutionary process to be maximally attractive to female birds—as, in turn, were the preferences of female birds so as to discriminate better among male plumages. It’s an iterative, co-adaptive process, each animal adapting over many generations to serve the other. A similar process occurs between males and females of other species, between co-adaptive life forms across species, and even between animals and plants.
    Fruits and flowers provide an excellent example of the co-evolution of plants and animals. Nature’s evolutionary process made flowers to be attractive to birds and bees, the better to spread their pollen, and fruits to be attractive to primates and other animals, the better to spread their seeds. Fruits and flowers tend to be symmetrical, rounded, smooth, pleasant to the touch, and colorful. Flowers have pleasant odors, and most fruits taste sweet, the better to attract animals and people who will eat them and then spread the seeds, whether by spitting or defecation. In this co-evolution of design, the plants change so as to attract animals, while the animals change so as to become attracted to the plants and fruits. The human love of sweet tastes and smells and of bright, highly saturated colors probably derives from this coevolution of mutual dependence between people and plants.
    The human preference for faces and bodies that are symmetrical presumably reflects selection of the fittest; non-symmetrical bodies probably are the result of some deficiency in the genes or the maturation process. Humans select for size, color, and appearance, and what you are biologically disposed to think of as attractive derives from these considerations. Sure, culture plays a role, so that, for example, some cultures prefer fat people, others thin; but even within those cultures, there is agreement on what is and is not attractive, even if too thin or too fat for specific likes.
    When we perceive something as “pretty,” that judgment comes directly from the visceral level. In the world of design, “pretty” is generally frowned upon, denounced as petty, trite, or lacking depth and substance—but that is the designer’s reflective level speaking (clearly trying to overcome an immediate visceral attraction). Because
designers want their colleagues to recognize them as imaginative, creative, and deep, making something “pretty” or “cute” or “fun” is not well accepted. But there is a place in our lives for such things, even if they are simple.
    You can find visceral design in advertising, folk art and crafts, and children’s items. Thus, children’s toys, clothes, and furniture will often reflect visceral principles: bright, highly saturated primary colors. Is this great art? No, but it is enjoyable.
    Adult humans like to explore experiences far beyond the basic, biologically wired-in preferences. Thus, although bitter tastes are viscerally disliked (presumably because many poisons are bitter), adults have learned to eat and drink numerous bitter things, even to prefer them. This is an “acquired taste,” so called because people have had to learn to overcome their natural inclination to dislike them. So, too, with crowded, busy spaces, or noisy ones, and discordant, nonharmonic music, sometimes with irregular beats: all things that are viscerally negative but that can be reflectively positive.
    The principles underlying visceral design are wired in, consistent across people and cultures. If you design according to these rules, your design will always be attractive, even if somewhat simple. If you design for the sophisticated, for the reflective level, your design can readily become dated because this