How Evolution Shapes Our Loves and Fears
See a snake, and many of us shiver. Hear a symphony, we sigh. A stroll through a garden can bring comfort and pleasure. But why? In his slim but rich new book Snakes, Sunrises, and Shakespeare, Gordon Orians, a professor emeritus of biology at the University of Washington in Seattle, explores how evolution has shaped our emotional responses to the environment and each other. Here, we offer a few tidbits:
Monsters under the Bed
Most savanna primates sleep in trees; so did our ancestors. Females were more likely to sleep in trees than males—they were lighter and more agile than the males, but also smaller and more vulnerable to savanna predators. As such, females should be particularly alert to attacks by predators from below. Males, on the other hand, sleeping on the ground, should be more attentive to side attacks. Three-to-four-year-old boys and girls are equally fearful at night, but boys are more afraid of danger to one side—the monster in the closet—while girls are more fearful of something dangerous below—the monster under the bed.
The Musical Ape
Charles Darwin first proposed that vocal communication in general, and music in particular, had developed as a result of sexual selection. Darwin appears to have been right! Females of some species of birds are more strongly attracted to males with larger song repertoires. Song elaboration in humpback whales is probably also favored by sexual selection. Why should females pay attention? Learning and producing songs requires a specialized neural system that develops when the individual is growing rapidly and many other physiological and anatomical systems are competing for a limited energy supply. Therefore, a male bird that sings vigorously and well is advertising his health and fitness.
A Snake in the Grass
Our ancestors would have benefited from an ability to detect hidden, stationary predators from glimpses of only small parts of them. Tessellated patterns are rare in nature but common among snakes. Yet cells of the mammalian visual system are highly stimulated by such patterns. The system readily detects scale patterns in peripheral vision, where we are most likely to spot a snake. The neural system responds selectively to angles and edges, features that enhance our ability to detect snakes against a background during daylight. Our neural fear module increases our ability to detect motionless snakes, even when we are unaware that we have seen them.
Goes Down Smooth
Every human society has discovered the medicinal and psychological benefits of alcohol. Other animals are attracted to alcohol, too. Vertebrates inevitably ingest alcohol when they eat ripe and rotting fruit. Orangutans and elephants travel for miles to find fermented fruits. The “drunken monkey” hypothesis of Robert Dudley proposes that a strong attraction to the smell and taste of alcohol helps animals find ripe fruit. Overripe fruit on the ground may have ethanol concentrations as high as four percent. However, when given a choice in the lab, animals typically prefer fruits with less ethanol. Getting drunk in a world full of predators is not a good idea.
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