The neural selection and the emergence of ‘beauty canons’ as signaling codes in co-evolving species

Widespread opinion wants beauty to be pleasant and aimless, this assumption biased Darwin's explanation of sexual selection. Conversely, Wallace hypothesized that showy and symmetric sexual traits correlate with vigor and health and he placed ‘aesthetic’ preferences within the natural selection. The controversy has continued until today. To understand the role of beauty canons in communication, the focus was on the flower-pollinator cooperative system as a model, were flower evolution embodies the natural history of pollinators' preferences. Optimum for a signal requires energy efficiency, high signal-to-noise ratio, and intelligibility. It involves pollinator perception mechanisms that, in turn, induce co-evolutionary feedback on signal traits. In fact, the flowers physical and hedonic properties correlate with the basic perceptual, motivational, emotional, and learning mechanisms of pollinators. It is proposed that pollinator behavior, unmasking a preference, reveals the ability to evaluate an expected benefit. Features such as a relative simplicity, redundancy, and regularity of stimuli facilitate perception and memorization and are essential elements for communication between co-evolving species. They improve signaling to satisfy the need for easy and fast recognition. With these properties, a stimulus is adaptive and rewarding per se and may be an ideal conditioned stimulus in associative learning. Among the most conspicuous signals, pollinators learn to recognize and choose those associated with nectar, thus favoring the evolution of flowers that are not only ‘beautiful’ but also ‘honest’ in reporting a reward. Beauty is an emergent property, and studying communication and perception we may understand the origin of some beauty canons.