The Best American Science and Nature Writing 2020

by Michio Kaku

  According to the adaptive model of beauty, the chucks must convey something about the males’ fitness. As it happens, larger males, which produce the deepest and sexiest chucks, are also the most adept at mating, because they are closer in size to females. (Frog sex is a slippery affair, and a diminutive male is more likely to miss his target.) Moreover, the túngara frog has an inner organ tuned to 2,200 hertz, which is close to the dominant frequency of a chuck. Together, these facts seem to indicate that the túngara’s puddle-side serenade is an example of adaptive mate choice: females evolved ears tuned to chucks because they indicate the biggest and most sexually skilled males.

  Ryan’s research revealed a stranger story. When he examined the túngara frog’s family tree, he discovered that eight frog species closely related to the túngara also have inner ear organs sensitive to frequencies of about 2,200 hertz, yet none of them produce chucks in their mating call. Ryan thinks that eons ago, the ancestor of all these species probably evolved an inner ear tuned to roughly 2,200 hertz for some long-abandoned purpose. The túngara later revived this neglected auditory channel, probably by happenstance. Male frogs that happened to burp out a few extra notes after whining were automatically favored by females—​not because they were more suitable mates, but simply because they were more noticeable.

  Like the glistening scales on the surfperch and swordtails that Cummings studied, the túngara’s costly mating call did not evolve to convey any pragmatic information about health or fitness. But that doesn’t mean that these traits were arbitrary. They were the result of specific, discernible aspects of the animals’ environments, anatomy, and evolutionary legacy. “I took a real beating when I suggested this idea in 1990,” Ryan says. “It was very widely criticized. But now sensory bias is considered an important part of the evolution of these preferences.”

  During our walk at Hammonasset, while admiring seabirds from shore-side cliffs, I asked Prum about sensory bias. He said it could not possibly explain the staggering diversity and idiosyncrasy of sexual ornaments—​the fact that every closely related sparrow species has a unique embellishment, for example. Prum sees sensory bias as just another way to maintain the predominant “adaptive paradigm” that refuses to acknowledge his theory of aesthetic evolution. Tellingly, Prum and Ryan do not discuss each other’s work in their recent books.

  While mulling over the similarities and discrepancies between Prum’s ideas and those of his peers, I kept returning to a passage in his book. In 2010, Prum and his colleagues revealed that a crow-size dinosaur called Anchiornis huxleyi was beautifully adorned: gray body plumage, an auburn mohawk, and long white limb feathers with black spangles. Why dinosaurs originally evolved feathers has long perplexed scientists. At first, layers of fuzzy filaments, similar to a chick’s down, most likely helped dinosaurs repel water and regulate body temperature. But what explains the development of broad, flat feathers like those found on Anchiornis? Flight is the intuitive answer, but the first planar feathers were probably too primitive for flight or gliding, lacking the distinct asymmetry that makes birds’ feathers aerodynamic. In his book, Prum advocates for an alternative hypothesis that has been gaining support: large feathers evolved to be beautiful.

  The aesthetic possibilities of fuzzy down are limited. “The innovative planar feather vane, however, creates a well-defined, two-dimensional surface on which it is possible to create a whole new world of complex color patterns within every feather,” Prum writes. Only later did birds co-opt their big, glamorous plumes for flight, which is probably a key reason that some of them survived mass extinction 66 million years ago. Birds transformed what was once mere frippery into some of the most enviable adaptations on the planet, from the ocean-spanning breadth of an albatross to the torpedoed silhouette of a plunging falcon. Yet they never abandoned their sense of style, using feathers as a medium for peerless pageantry. A feather, then, cannot be labeled the sole product of either natural or sexual selection. A feather, with its reciprocal structure, embodies the confluence of two powerful and equally important evolutionary forces: utility and beauty.

  Most of the scientists I spoke with said that the old dichotomy between adaptive adornment and arbitrary beauty, between “good genes” and Fisherian selection, is being replaced with a modern conceptual synthesis that emphasizes multiplicity. “Beauty is something that arises from a host of different mechanisms,” says Gil Rosenthal, an evolutionary biologist at Texas A&M University and the author of the new scholarly tome Mate Choice. “It’s an incredibly multilayered process.”

  The environment constrains a creature’s anatomy, which determines how it experiences the world, which generates adaptive and arbitrary preferences, which loop back to alter its biology, sometimes in maladaptive ways. Beauty reveals that evolution is neither an iterative chiseling of living organisms by a domineering landscape nor a frenzied collision of chance events. Rather, evolution is an intricate clockwork of physics, biology, and perception in which every moving part influences another in both subtle and profound ways. Its gears are so innumerable and dynamic—​so susceptible to serendipity and mishap—​that even a single outcome of its ceaseless ticking can confound science for centuries.

  * * *

  On my last day in Austin, while walking through a park, I encountered a common grackle hunting for insects in the grass. His plumage appeared black as charcoal at first, but as he moved, it shimmered with all the colors of an oil slick. Every now and then, he stopped in place, inflated his chest, and made a sound like a rusty swing set. Perhaps dissatisfied with the local fare, or uncomfortable with my presence, he flew off.

  In his absence, my attention immediately shifted to something his presence had obscured—​a golden columbine bush. From a distance, its flowers resembled medieval illustrations of comets, big and bold with long, trailing streamers. Up close, I was struck by the complexity of a single blossom: a large yellow star wreathed a cluster of five tubular petals, shaped like angel’s trumpets and pooled with nectar. A tuft of pollen-tipped filaments fizzed through the very center. Viewed from above, the flowers looked like huddles of tiny birds with their beaks pressed together and wings flared. The name “columbine” comes from the Latin for “dovelike.”

  Why are flowers beautiful? Or, more precisely: why are flowers beautiful to us? The more I thought about this question, the more it seemed to speak to the nature of beauty itself. Philosophers, scientists, and writers have tried to define the essence of beauty for thousands of years. The plurality of their efforts illustrates the immense difficulty of this task. Beauty, they have said, is: harmony; goodness; a manifestation of divine perfection; a type of pleasure; that which causes love and longing; and M = O/C (where M is aesthetic value, O is order, and C is complexity).

  Evolutionary psychologists, eagerly applying adaptive logic to every facet of behavior and cognition, have speculated that the human perception of beauty emerges from a set of ancient adaptations: perhaps men like women with large breasts and narrow waists because those features signal high fertility; symmetrical faces may correlate with overall health; maybe babies are irresistibly cute because their juvenile features activate the caregiving circuits in our brains. Such claims sometimes verge on the ludicrous: the philosopher Denis Dutton has argued that people around the world have an intrinsic appreciation for a certain type of landscape—​a grassy field with copses of trees, water, and wildlife—​because it resembles the Pleistocene savannas where humans evolved. In a TED Talk, Dutton explains that postcards, calendars, and paintings depicting this universally beloved landscape usually include trees that fork near the ground because our ancestors relied on their conveniently low branches to scramble away from predators.

  Of course, it is undeniable that we, like all animals, are products of evolution. Our brains and sensory organs are just as biased as any other creature’s. Our inherited anatomy, physiology, and instincts have undoubtedly shaped our perception of beauty. In their recent books, Richard Prum and Michael Ryan
synthesize research on animals and people, exploring possible evolutionary explanations for our own aesthetic tastes. Ryan is particularly interested in the innate sensitivities and biases of our neural architecture: he describes how our visual system, for example, may be wired to notice symmetry. Prum stresses his conviction that in humans, as in birds, many types of physical beauty and sexual desire have arbitrarily coevolved without reference to health or fertility. What complicates their respective arguments is the overwhelming power of human culture. As a species, we are so thoroughly saturated with symbolism, ritual, and art—​so swayed by rapidly changing fashions—​that it is more or less impossible to determine just how much an aesthetic preference owes to evolutionary history as opposed to cultural influence.

  Perhaps more than any other object of aesthetic obsession, flowers expose the futility of trying to contain beauty in a single theoretical framework. Consider how flowers came to be and how we grew to love them: 150 million years ago many pollen-producing plants depended on the wind to spread their pollen and reproduce. But certain insects, perhaps beetles and flies, began to eat those protein-rich pollen grains, inadvertently transporting them from one plant to another. This proved to be a much more efficient means of fertilization than capricious air currents. Plants with the richest and most obvious sources of pollen were especially successful. Likewise, insects that were particularly adept at finding pollen had an advantage over their peers.

  Through a long process of coevolution, plants and pollinators transformed one another. Some plants began to modify their leaves into proto-flowers: little flags that marked the location of their pollen. Bold colors and distinctive shapes helped them stand out in a tangle of green. Strong aromas and ultraviolet beacons played upon pollinators’ senses. Nectar sweetened the deal. Insects, birds, and mammals began competing for access, evolving wings, tongues, and brains better suited to the quest for floral sustenance. As the pressure from both parties intensified, plants and their pollinators formed increasingly specific relationships, hurtling each other toward aesthetic and adaptive extremes—​a bird that hums and hovers like an insect, an orchid that mimics the appearance and scent of a female bee.

  Many millions of years later, flowers enchanted yet another species. Perhaps the initial attraction was purely utilitarian: the promise of fruit or grain. Maybe we were captivated by their consonance of color, form, and aroma. Whatever the case, we adopted numerous flowering plants into an expanding circle of domesticated species. We brought them into greenhouses and laboratories, magnifying their inherent beauty, creating new hybrids, and tailoring their features to our individual tastes. We contracted orchid delirium and tulip mania, and we have never fully recovered. The flower began as a plea and became a phenomenon.

  If there is a universal truth about beauty—​some concise and elegant concept that encompasses every variety of charm and grace in existence—​we do not yet understand enough about nature to articulate it. What we call beauty is not simply one thing or another, neither wholly purposeful nor entirely random, neither merely a property nor a feeling. Beauty is a dialogue between perceiver and perceived. Beauty is the world’s answer to the audacity of a flower. It is the way a bee spills across the lip of a yawning buttercup; it is the care with which a satin bowerbird selects a hibiscus bloom; it is the impulse to re-create water lilies with oil and canvas; it is the need to place roses on a grave.

  SARAH KAPLAN

  Ghosts of the Future

  from The Washington Post

  If the history of Earth is condensed to fit in a single twenty-four-hour day, life emerges sometime before dawn. Photosynthesis evolves around midmorning, and the atmosphere becomes oxygen-rich right before lunch. But most of the day is utterly boring; all organisms are microscopic and occupied with little more than belching gasses and oozing slime.

  It isn’t till 9 p.m., about half a billion years before the present, that we see the first complex, multicellular beings. Scientists call this juncture the “Cambrian explosion”—​the moment when billions of years of bacteria gave way to the rapidly evolving beings we know as animals. This evolutionary burst is responsible for every elephant, every fly, every bowlegged amphibian and wriggling worm, every complex creature that ever walked, swam, flew, or scurried on this Earth. And I’m about to witness it firsthand.

  “Ready to go back in time?” asks Ardelle Hynes, a cheerful, ponytailed ranger at Yoho National Park in British Columbia.

  It’s a drizzly July morning, and I’m huffing in Hynes’s wake as we ascend a sheer mountainside in the Canadian Rockies. Our destination, high on the cliff face, is a jumble of 510-million-year-old rocks known as the Burgess Shale.

  Formed during the middle part of the Cambrian period, the shale boasts tens of thousands of perfectly preserved fossils from the dawn of the animal kingdom. Many were soft-bodied organisms whose existence in most other places has been lost to the ravages of time. This wealth of small, strange specimens has shaped scientists’ understanding of evolution and offered insight into the link between Earth’s climate and the life it can support, making the Burgess Shale one of the most precious and important fossil sites in the world.

  This remarkable record exists only because of a catastrophic underwater landslide that buried the organisms in a deluge of sediment millions of years ago. The sand was so fine it would have filled the animals’ gills and the hinges of their legs, trapping and suffocating them. The high alkalinity of the oceans, combined with the utter absence of oxygen, would have held at bay the bacteria that would otherwise decompose an organism’s soft and squishy parts.

  “Think about all the factors that had to come together for us to be able to experience this,” Hynes says. The animals had to die in a manner that allowed them to fossilize. Those conditions had to persist for millions upon millions of years. The rocks had to be lifted from the bottom of the ocean to the top of the world by the action of tectonics, and then scraped by the slow crawl of glaciers to reveal the treasures they contained. And, finally, an enterprising ape species had to evolve sufficient intelligence to invent the field of geology, hike up this mountain, and recognize the significance of what they found. “Aren’t we lucky?” Hynes says.

  I take a breath of sharp, clean air and survey the spruce forest, the ice-capped mountains cloaked in wisps of fog. Hynes gives me a fossil, a piece of this planet’s history, and I feel its heft in my hand. I see what she means.

  But then I think of the invasive bark beetles, spurred by a warming climate, that are eating away at this forest. I think of retreating glaciers and vanishing species and all the consequences of unchecked carbon consumption that are still to come.

  I think of the United Nations scientists who declared last year that we had just over a decade to get climate change under control, and the officials meeting in Madrid this month who have fallen far short of the commitments needed to make that happen.

  Life on Earth has been evolving for nearly 4 billion years. Yet only now, as the geological clock strikes midnight, is there a creature capable of looking back at that history and appreciating it. Only now, as our own actions imperil this extraordinary and singular planet, do humans have a chance to comprehend all that is about to be lost.

  What a profound responsibility that is. What a beautiful gift.

  * * *

  As we hike, Hynes paints a picture of how the landscape would have looked half a billion years ago. The continents were clumped into two large masses, empty but for some slimy microbial mats. Without land plants to prevent erosion, sediment was constantly being swept out to sea, where it settled in thick, silty layers.

  It’s hard for me to envision. At most points in its history, humans wouldn’t recognize our planet at all.

  Researchers debate what caused the single-celled microbes of the Proterozoic (or “simple life”) eon to evolve into the complex organisms seen in the Burgess Shale. Perhaps it was climate change—​Earth was slowly recovering from an intense ice age—​or the gre
ater availability of oxygen in the atmosphere. Others have suggested that some key biological innovation, like the development of vision or the rise of predators, set off an evolutionary arms race that resulted in ever-more-complex creatures.

  After trudging for 2.5 miles and 2,000 feet of elevation gain, we round a bend in the trail and are suddenly at the quarry. Gray and brown slabs of shale litter a football field–size expanse of mountainside. Hynes instructs my fellow hikers and me to set aside our trekking poles, which can damage fossils. Then we set out across the rocks.

  It’s difficult to know where to put my feet; nearly every stone seems to bear at least a fragment of an ancient animal. Hynes points out a fossil resembling a slice of pineapple. These are the mouth parts of Anomalocaris—​the bizarre, dog-size apex predator of the Cambrian seas.

  Weirdness seems to be the defining characteristic of Burgess Shale organisms. Hynes shows us illustrations of Opabinia, an oddball with five eyes and a vacuum cleaner nozzle for a nose, and the monstrous Hallucigenia, which boasted eight pairs of legs and an equal number of conical spines. The ancestor of all modern vertebrates, including fish, birds, and humans, was Pikaia, a wriggling eel-like organism no longer than your big toe. My favorites are the trilobites, distant relatives of today’s horseshoe crabs, with jointed legs and shells of overlapping plates that almost look like ribs. They thrived for 300 million years, through the drifting of continents and the rise and fall of sea levels, the flourishing of coal age plants, the invention of the backbone.