The Art Instinct_ Beauty, Pleasure, & Human Evolution - Denis Dutton [75]
Sexual selection is ubiquitous in the animal kingdom and throws light on curious features of animals that natural selection is powerless explain. Not only striking plumage but such characteristics as body symmetry, healthy skin, shiny fur, agility, tireless courtship dancing, intricate aerial maneuvers, musculature, and gross strength are in part or in whole products of sexual selection. The typical pattern is that some trait of animal that evolved by a straightforward process of natural selection commandeered by sexual selection and either greatly accentuated or completely transformed into a fitness signal. Thus birds evolve feathers warmth and for flight. But feathers are susceptible to coloration, can grown in an immense variety of forms, and can act as visible signs health and genetic fitness. Natural selection can produce drab feathers exactly to match a habitat background and achieve near invisibility in nest. Sexual selection classically eschews camouflage strategies, going exactly the opposite direction to produce gaudy, flamboyant shapes colors. This ostentation—both dangerously conspicuous and wasteful— not an incidental by-product of some evolutionary process but is the very point of sexual selection and fitness display.
Sexual selection is sometimes regarded as a special case of natural since both processes in the most general sense increase gene propagation, the survival of a ge netic line. However, as Darwin himself fully appreciated, the intrinsic mechanisms of natural and sexual selection fundamentally different. In natural selection, random mutation and selective capacity, sperm production, binocular vision, and so forth. Still within the realm of natural selection are evolved dispositions, emotions, and behavior patterns that have direct bearing on survival or the will to reproduce: of heights, wariness of growling animals, finding poisonous plant bitter and repellent, a taste for sweet and fat, and sexual plea sure. well-functioning liver and a general fear of snakes are both “healthy” in the sense that they were naturally selected for in prehistory and so remain with us today. For each one of us, our grandmothers and grandfathers tens thousands of generations removed form a continuous line of people who were fit to live long enough to reproduce. These survivors passed their traits on to us, unlike their less fit siblings who died—of liver failure snakebite, for instance—before they could reproduce. The unlucky siblings are our aunts and uncles thousands of generations removed; they our direct ancestors. These were joined in death by other of our more distant relatives, countless people and proto-people who did not find high places scary nor snakes parpaticularly alarming, for whom fat and sweet were especially tasty, and who in their reproductive prime took little plea from sexual adventures.
However, a distinctly new factor is introduced into the logic of evolution by sexual selection. Where natural selection pits a slowly mutating species against opportunities and demands of an external environment, sexual selection shifts the focus to the relation of members of a species each other. These relations fall into two broad classes of competition. First, members of the same sex compete against each other for either best mate or the largest number of mates. This kind of sexual selection still somewhat resembles natural selection: it typically involves aggressive fighting among males for females in a winner-takes-all situation. With elephant seals, sheer body size and constant guarding can give large, mature male access to 80 percent or more of the females in an extensive beach territory. This kind of male competitive struggle, also observed among such animals as elk and bighorn goats, can lead to fights to the death for access to females.
Although they are a frequent topic of fictional literature worldwide, dramatic duels to the death for the hand