So the next time you’re in airport security and frustrated by that disorganized person in front of you who can’t seem to get it through his head that his belt, wallet, and watch will all set off the alarm, just take a deep breath and think of the possibly habitable distant oceans we now know of, thanks to the same beautiful physics that’s driving you nuts as you contemplate missing your plane.
PLATE TECTONICS ELEGANTLY VALIDATES CONTINENTAL DRIFT
PAUL SAFFO
Technology forecaster; managing director, foresight, Discern Analytics; consulting associate professor, Stanford University
Plate tectonics is a breathtakingly elegant explanation of a beautiful theory: continental drift. Both puzzle and answer were hiding in plain sight, right under our feet. Generations of globe-twirling schoolchildren have noticed that South America’s bulge seems to fit into the gulf of Africa and that Baja California looks as if it had been cut out of the Mexican mainland. These and other more subtle clues led Alfred Wegener to propose to the German Geological Society in 1912 that the continents had once formed a single landmass. His beautiful theory was greeted with catcalls and scientific brickbats.
The problem was that Wegener’s beautiful theory lacked a mechanism. Critics sneeringly pronounced that the lightweight continents could not possibly plow through a dense and unyielding oceanic crust. No one, including Wegener, could imagine a force that could cause the continents to move. It didn’t help that Wegener was a meteorologist poaching in geophysical territory. He would die on an expedition to Greenland in 1930, his theory out of favor and all but forgotten.
Meanwhile, hints of a mechanism were everywhere but at once too small and too vast to be seen. Like ants crawling on a globe, puny humans missed the obvious. It would take the arrival of powerful new scientific tools to reveal the hidden forensics of continental drift. Sonar traced mysterious linear ridges running zipperlike along ocean floors. Magnetometers towed over the seabed painted symmetrical zebra-striped patterns of magnetic reversals. Earthquakes betrayed plate boundaries to listening seismographs. And radiometric dating laid out a scale reaching into deep time.
Three decades after Wegener’s death, the mechanism of plate tectonics emerged with breathtaking clarity. The continents weren’t plowing through anything—they were rafting atop the crust, like marshmallows stuck in a sheet of cooling chocolate. And the oceanic crust was moving like a conveyor, with new crust created in midocean spreading centers and old crust subducted, destroyed, or crumpled upward into vast mountain ranges at the boundaries where plates met.
Elegant explanations are the Kuhnian solvent that leaches the glue from old paradigms, making space for new theories to take hold. Plate tectonics became established beyond a doubt in the mid-1960s. Contradictions suddenly made sense, and ends so loose no one thought they were remotely connected came together. Continents were seen for the wanderers they were. The Himalayas were recognized as the result of a pushy Indian plate smashing into its Eurasian neighbor, and it became obvious that an ocean was being born in Africa’s Great Rift Valley. Mysteries fell like dominoes before the predictive power of a beautiful theory and its elegant explanation. The skeptics were silenced and Wegener was posthumously vindicated.
WHY SOME SEA TURTLES MIGRATE
DANIEL C. DENNETT
Philosopher; university professor and codirector, Center for Cognitive Studies, Tufts University; author, Breaking the Spell: Religion as a Natural Phenomenon
My choice is an explanation that delights me. It may be true and may be false—I don’t know, but probably somebody who reads Edge will be able to say, authoritatively, with suitable references. I am eager to find out. I was told some years ago that the reason that some species of sea turtles migrate all the way across the South Atlantic to lay their eggs on the east coast of South America after mating on the west coast of Africa is that when the behavior started, Gondwana was just beginning to break apart (that would be between 130 and 110 million years ago), and these turtles were just swimming across the narrow strait to lay their eggs. Each year the swim was a little longer—maybe an inch or so—but who could notice that? Eventually they were crossing the ocean to lay their eggs, having no idea, of course, why they would do such an extravagant thing.
What is delicious about this example is that it vividly illustrates several important evolutionary themes: the staggering power over millions of years of change so gradual it is essentially unnoticeable; the cluelessness of much animal behavior, even when it is adaptive; and of course the eye-opening perspective that evolution by natural selection can offer to the imagination of the curious naturalist. It also demonstrates either the way an evolutionary hypothesis can be roundly refuted by discoverable facts (if it is refuted) or the way it can be supported by further evidence (if in fact it is so supported).
An attractive hypothesis such as this is the beginning, not the end, of the inquiry. Critics often deride evolutionary hypotheses about prehistoric events as “just-so stories,” but as a blanket condemnation this charge should be rejected out of hand. Thousands of such hypotheses—first dreamed up on slender evidence—have been tested and confirmed beyond a reasonable doubt. Thousands of others have been tested and disconfirmed. They were just-so stories until they weren’t, in other words. That’s the way science advances.
I have noticed that there is a pattern in the use of the “just-so story” charge: With almost no exceptions, it is applied to hypotheses about human evolution. Nobody seems to object that we can’t know enough about the selective environment leading to whales or flowers for us to hold forth so confidently about how and why whales and flowers evolved as they did. So my rule of thumb is: If you see the “just-so story” epithet hurled, look for a political motive. You’ll almost always find one. While it is no doubt true that some evolutionary psychologists have offered hypotheses about human evolution for which there is still only slender supporting evidence, and while it is also no doubt true that some evolutionary psychologists have been less than diligent in seeking further evidence to confirm or disconfirm their favorite hypotheses, this is at most a criticism of the thoroughness of some researchers in the field, not a condemnation of their method or their hypotheses. The same could be said about many other topics in evolutionary biology.
A HOT YOUNG EARTH: UNQUESTIONABLY BEAUTIFUL AND STUNNINGLY WRONG
CARL ZIMMER
Science writer; author, A Planet of Viruses
Around 4.567 billion years ago, a giant cloud of dust collapsed in on itself. At the center of the cloud, our sun began to burn, while the outlying dust grains began to stick together as they orbited the new star. Within a million years, those clumps of dust had become protoplanets. Within about 50 million years, our own planet had already reached about half its current size. As more protoplanets crashed into Earth, it continued to grow. All told, it may have taken another 50 million years to reach its full size, a time during which a Mars-sized planet crashed into it, leaving behind a token of its visit—our moon.
The formation of the Earth commands our greatest powers of imagination. It is primordially magnificent. But elegant is not the word I’d use to describe the explanation I just sketched out. Scientists did not derive it from first principles. There is no equivalent of e = mc2 that predicts how the complex violence of the early solar system produced a watery planet that could support life. In fact, the only reason we now know so much about how the Earth formed is because geologists freed themselves from a seductively elegant explanation that was foisted on them 150 years ago. It was unquestionably beautiful, and stunningly wrong.
The explanation was the work of one of the greatest physicists of the 19th century, William Thomson (aka Lord Kelvin). Kelvin’s accomplishments ranged from the concrete (figuring out how to lay a telegraph cable from Europe to America) to the abstract (the first and second laws of thermodynamics). Kelvin spent much of his career writing equations that could let him calculate how fast hot things got cold. He realized that he could use these equ
ations to estimate how old the Earth is. “The mathematical theory on which these estimates are founded is very simple,” Kelvin declared when he unveiled it in 1862.*
At the time, scientists generally agreed that the Earth had started out as a ball of molten rock and had been cooling ever since. Such a birth would explain why rocks are hot at the bottom of mine shafts: The surface of the Earth was the first part to cool, and ever since, the remaining heat inside the planet had been flowing out into space. Kelvin reasoned that over time the planet should steadily grow cooler. He used his equations to calculate how long it should take for a molten sphere of rock to cool to Earth’s current temperature, with its observed rate of heat flow. His verdict was a brief 98 million years.
Geologists howled in protest. They didn’t know how old the Earth was, but they thought in billions of years, not millions. Charles Darwin—who was a geologist first and a biologist later—estimated that it had taken 300 million years for a valley in England to erode into its current shape. The Earth itself, Darwin argued, was far older. And when he published his theory of evolution he took it for granted that the Earth was inconceivably old; the luxury of time provided room for evolution to work slowly and imperceptibly.
Kelvin didn’t care. His explanation was so elegant, so beautiful, so simple, that it had to be right. It didn’t matter how much trouble it caused for other scientists who were ignoring thermodynamics. In fact, Kelvin made even more trouble for geologists when he took another look at his equations. He decided his first estimate had been too generous. The Earth might be only 10 million years old.
It turned out that Kelvin was wrong, but not because his equations were ugly or inelegant. They were flawless. The problem lay in the model of the Earth to which Kelvin applied his equations.
The story of Kelvin’s refutation got a bit garbled in later years. Many people (myself included) have mistakenly claimed that his error stemmed from his ignorance of radioactivity. Radioactivity was not discovered until the early 1900s, as physicists worked out quantum physics. The physicist Ernest Rutherford declared that the heat released as radioactive atoms broke down inside the Earth kept it warmer than it would be otherwise. Thus a hot Earth did not have to be a young Earth.
It’s true that radioactivity does give off heat, but there isn’t enough inside the planet to account for the heat flowing out of it. Instead, Kelvin’s real mistake was assuming that the Earth was just a solid ball of rock. In reality, the rock flows like syrup, its heat lifting it up toward the crust, where it cools and then sinks back into the depths once more. This stirring of the Earth is what causes earthquakes, drives old crust down into the depths of the planet, and creates fresh crust at ocean ridges. It also drives heat up into the crust at a much greater rate than Kelvin envisioned.
That’s not to say that radioactivity didn’t have its part to play in showing that Kelvin was wrong. Physicists realized that the tick-tock of radioactive decay created a clock they could use to estimate the age of rocks with exquisite precision. Thus we can now say that the Earth is not just billions of years old but 4.567 billion.
Elegance unquestionably plays a big part in the advancement of science. The mathematical simplicity of quantum physics is lovely to behold. But in the hands of geologists, quantum physics has brought to light the glorious, messy, and very inelegant history of our planet.
SEXUAL-CONFLICT THEORY
DAVID M. BUSS
Professor of psychology, University of Texas, Austin; coauthor (with Cindy M. Meston), Why Women Have Sex
A fascinating parallel has occurred in the traditionally separate disciplines of evolutionary biology and psychology. Biologists historically viewed reproduction as an inherently cooperative venture. A male and female would couple for the shared goal of reproduction of mutual offspring. In psychology, romantic harmony was presumed to be the normal state. Major conflicts within romantic couples were, and still are, typically seen as signs of dysfunction. A radical reformulation, embodied by sexual-conflict theory, changes these views.
Sexual conflict occurs whenever the reproductive interests of an individual male and individual female diverge—or, more precisely, when the “interests” of their genes diverge. Sexual-conflict theory defines the many circumstances in which discord is predictable and entirely expected.
Consider deception on the mating market. If a man is pursuing a short-term mating strategy and the woman in whom he is sexually interested is pursuing a long-term mating strategy, conflict between them is virtually inevitable. Men are known to feign long-term commitment, interest, or emotional involvement for the goal of casual sex, interfering with women’s long-term mating strategy. Men have evolved sophisticated strategies of sexual exploitation; conversely, women sometimes present themselves as costless sexual opportunities and then invade a man’s mating mind so successfully that he wakes up one morning and realizes he can’t live without her—one version of the bait-and-switch tactics in women’s evolved arsenal.
Once coupled in a long-term romantic union, a man and a woman often still diverge in their evolutionary interests. Sexual infidelity on the part of the woman might benefit her by securing superior genes for her progeny, an event with catastrophic costs to her hapless partner, who unknowingly devotes resources to a rival’s child. From a woman’s perspective, a man’s infidelity risks diversion of precious resources to rival women and their children and poses the danger of losing the man’s commitment entirely. Sexual infidelity, emotional infidelity, and resource infidelity are such common sources of sexual conflict that theorists have coined distinct phrases for each.
But all is not lost. As evolutionist Helena Cronin has eloquently noted, sexual conflict arises in the context of sexual cooperation. The following evolutionary conditions for sexual cooperation are well specified: when relationships are entirely monogamous; when there is zero probability of infidelity or defection; when the couple produces offspring, the shared vehicles of their genetic cargo; and when joint resources cannot be differentially channeled, such as to one set of in-laws versus another. These conditions are sometimes met, leading to great love and harmony between a man and a woman.
The prevalence of deception, sexual coercion, stalking, intimate-partner violence, murder, and the many forms of infidelity reveal that conflict between the sexes is ubiquitous. Sexual-conflict theory, a logical consequence of modern evolutionary genetics, provides the most beautiful theoretical explanation for these darker sides of human sexual interaction.
THE SEEDS OF HISTORICAL DOMINANCE
DAVID PIZARRO
Associate professor of psychology, Cornell University
One of the most elegant explanations I have ever encountered in the social sciences comes courtesy of Jared Diamond, outlined in his wonderful book Guns, Germs, and Steel. Diamond attempts to answer an enormously complex and historically controversial question—why certain societies achieved historical dominance over others—by appealing to a set of basic differences in the physical environments from which these societies emerged, such as differences in the availability of plants and animals suitable for domestication.
These differences, Diamond argues, gave rise to a number of specific advantages, such as greater immunity to disease, that were directly responsible for the historical success of some societies. I’m not an expert in this domain, so I realize that Diamond’s explanation might well be misguided—yet the appeal to such basic mechanisms in order to explain such a wide set of complex observations is so deeply satisfying that I hope he’s right.
THE IMPORTANCE OF INDIVIDUALS
HOWARD GARDNER
Hobbs Professor of Cognition and Education, Harvard Graduate School of Education; author, Truth, Beauty, and Goodness Reframed: Educating for the Virtues in the 21st Century
I consider myself a scientist, and the theory of evolution is central to my thinking. I am a social scientist and have been informed by insights from many social sciences, including economics. Yet I have little sympathy with hegemonic
attempts to explain all human behaviors via evolutionary psychology, via rational-choice economics, and/or by a combination of these two frameworks.
In a planet occupied now by nearly 7 billion inhabitants, I am amazed by the difference one human being can make. Think of classical music without Mozart or Stravinsky; of painting without Caravaggio, Picasso, or Pollock; of drama without Shakespeare or Beckett. Think of the incredible contributions of Michelangelo or Leonardo, or, in recent times, the outpouring of deep feeling at the death of Steve Jobs (or, for that matter, Michael Jackson or Princess Diana). Think of human values in the absence of Moses or Christ.
Alas, not all singular individuals make a positive difference. The history of the 20th century would be far happier had it not been for Hitler, Stalin, or Mao (or the 21st century without Bin Laden). But in reaction to these individuals, there sometimes arise more praiseworthy figures: Konrad Adenauer in Germany, Mikhail Gorbachev in the Soviet Union, Deng Xiaoping in China. These successors also make a signal difference.
I consider Mahatma Gandhi to be the most important human being of the last millennium. His achievements in India speak for themselves. But even if Gandhi had not contributed vital energy and leadership to his own country, he had enormous influence on peaceful resisters across the globe: Nelson Mandela in South Africa, Martin Luther King Jr. in the United States, and the solitary figures in Tiananmen Square in 1989 and Tahrir Square in 2011.
Despite the laudatory efforts of scientists to ferret out patterns in human behavior, I continue to be struck by the impact of single individuals, or of small groups, working against the odds. As scholars, we cannot and should not sweep these instances under the investigative rug. We should bear in mind anthropologist Margaret Mead’s famous injunction: “Never doubt that a small group of thoughtful committed citizens can change the world; indeed, it is the only thing that ever has.”
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