FRAMES OF REFERENCE
DIMITAR D. SASSELOV
Professor of astronomy, Harvard University; director, Harvard Origins of Life Initiative; author, The Life of Super-Earths: How the Hunt for Alien Worlds and Artificial Cells Will Revolutionize Life on Our Planet
Deep and elegant explanations relate to natural or social phenomena, and the observer often has no place in them. As a young student, I was fascinated to understand how frames of reference work—that is, to learn what it means to be an observer.
The reference-frame concept is central in physics and astronomy. For example, the study of flows relies most often on two basic frames: one in which the flow is described as it moves through space, called an Eulerian frame; and another, called a Lagrangian frame, which moves with the flow, stretching and bending as it goes. The equations of motion in the Eulerian frame seemed intuitively obvious to me, but I felt exhilarated when I understood the same flow described by equations in the Lagrangian frame.
It is beautiful. Let’s think of a flow of water, a winding river. You are perched on a hill by the riverbank, observing the water flow, which is marked by a multitude of floating tree leaves. The banks of the river, the details of the surroundings, provide a natural coordinate system, just as on a geographical map; you could almost create a mental image of fixed criss-crossing lines, your frame of reference. The river’s flow moves through that fixed map; you can describe the twists and turns of the currents and their changing speed, all thanks to this fixed Eulerian frame of reference, named after Leonhard Euler (1707–1783).
It turns out that you could describe the flow with equal success if, instead of standing safely atop the hill, you plunged into the river and floated downstream, observing the whirling motions of the tree leaves all around you. Your frame of reference—the one named after Joseph-Louis Lagrange (1736–1813)—is no longer fixed; instead, you’re describing all motions as relative to you and to one another. Your description of the flow will match exactly the description you achieved by observing from the hill, although the mathematical equations appear unrecognizably different.
To my younger self, back then, the transformation between the two frames looked like magic. It was not deep, perhaps, but it was elegant and extremely helpful. However, it was also just the start of a journey—a journey that would pull the old frames of reference out from under me. It started with the naive picture of an unmoving Earth as the absolute frame of Aristotle, soon to be rejected and replaced by Galileo with a frame of reference in which motion is not absolute. Oh, how I loved floating with Lagrange down Euler’s river, only to be unsettled again by the special relativity of Einstein and trying to comprehend the loss of simultaneity. And a loss it was.
A fundamental shift in our frame of reference, especially the one that defines our place in the world, deeply affects each and every one of us personally. We live and learn. The next generation is born into the new with no attachment to the old.
In science, it’s easy. But human frames of reference go beyond mathematics, physics, and astronomy. Do we know how to transform between human frames of reference successfully? Are they more often than not “Lagrangian” and relative? Perhaps we could take a cue from science and find an elegant solution. Or at least an elegant explanation.
EPIGENETICS—THE MISSING LINK
HELEN FISHER
Biological anthropologist, Rutgers University; author, Why Him? Why Her? How to Find and Keep Lasting Love
To me, epigenetics is the most monumental explanation to emerge in the social and biological sciences since Darwin proposed his theories of natural selection and sexual selection. More than 2,500 articles, many scientific meetings, the San Diego Epigenome Center and other institutes, a five-year Epigenomics Program launched in 2008 by the National Institutes of Health, and many other institutions, academic forums, and people are devoted to this new field. Although epigenetics has been defined in several ways, all are based on the concept that environmental forces can affect gene behavior, either turning genes on or off. As an anthropologist untrained in advanced genetics, I won’t attempt to explain the processes involved, although two basic mechanisms are known: One involves molecules known as methyl groups that latch on to DNA to suppress and silence gene expression; the other involves molecules known as acetyl groups, which activate and enhance gene expression.
The consequences of epigenetic mechanisms are likely to be significant. Scientists hypothesize that epigenetic factors play a role in the etiology of many diseases, conditions, and human variations, from cancers to clinical depression and mental illnesses to human behavioral and cultural variations.
Take the Moroccan Amazighs, or Berbers, people with highly similar genetic profiles who now reside in three different environments: Some roam the deserts as nomads, some farm the mountain slopes, some live in the towns and cities along the Moroccan coast. And depending on where they live, up to one-third of their genes are differentially expressed, reports researcher Youssef Idaghdour.*
For example, among the urbanites, some genes in the respiratory system are switched on—perhaps, Idaghdour suggests, to counteract their new vulnerability to asthma and bronchitis in these smoggy surroundings. Idaghdour and his colleagues propose that epigenetic mechanisms have altered the expression of many genes in these three Berber populations, producing their population differences.
Psychiatrists, psychologists, and therapists have long been preoccupied with our childhood experiences—specifically, how these sculpt our adult attitudes and behaviors. Yet they have focused on how the brain integrates and remembers these occurrences. Epigenetic studies provide a different explanation. For example, mother rats that spend more time licking and grooming their young during the first week after birth produce infants who later become better-adjusted adults. And researcher Moshe Szyf proposes that this behavioral adjustment occurs because epigenetic mechanisms are triggered during this critical period, producing a more active version of a gene that encodes a specific protein. Then this protein, via complex pathways, sets up a feedback loop in the hippocampus of the brain—enabling these rats to cope more efficiently with stress.*
These behavioral modifications remain stable through adulthood. However, Szyf notes that when specific chemicals were injected into the adult rats’ brains to alter these epigenetic processes and suppress this gene expression, these well-adjusted rats became anxious and frightened. And when different chemicals were injected to trigger epigenetic processes that instead enhance the expression of this gene, fearful adult rats (rats that had received little maternal care in infancy) became more relaxed.
Genes hold the instructions; epigenetic factors direct how those instructions are carried out. And as we age, scientists report, these epigenetic processes continue to modify and build who we are. Fifty-year-old twins, for example, show three times more epigenetic modifications than do three-year-old twins; and twins reared apart show more epigenetic alterations than those who grow up together. Epigenetic investigations are proving that genes are not destiny; but neither is the environment—even in people.
Shelley Taylor has shown this. Studying an allele (genetic variant) in the serotonin system, she and colleagues showed that the symptoms of depression are visible only when this allele is expressed in combination with specific environmental conditions. Moreover, Taylor maintains that individuals growing up in unstable households are likely to suffer all their lives with depression, anxiety, specific cancers, heart disease, diabetes, or obesity.* Epigenetics at work? Probably.
Even more remarkable, some epigenetic instructions are passed from one generation to the next. Transgenerational epigenetic modifications are now documented in plants and fungi and have been suggested in mice. Genes are like the keys on a piano; epigenetic processes direct how these keys are played—modifying the tune, even passing these modifications to future generations. Indeed, in 2010, scientists wrote in Science magazine that epigenetic systems are now regarded as heritable, self-perpetuating, and re
versible.
If epigenetic mechanisms can not only modulate our intellectual and physical abilities but also pass these alterations on to our descendants, epigenetics has immense and profound implications for the origin, evolution, and future of life on Earth. In coming decades, scientists studying epigenetics may understand how myriad environmental forces affect our health and longevity in specific ways, find cures for many human diseases and conditions, and explain intricate variations in human personality.
The 17th-century philosopher John Locke was convinced that the human mind is a blank slate upon which the environment inscribes personality. With equal self-assurance, others have been convinced that genes orchestrate our development, illnesses, and lifestyles. Yet social scientists failed for decades to explain the mechanisms governing behavioral variations between twins and among family members and culture groups. And biological scientists failed to pinpoint the genetic foundations of many mental illnesses and complex diseases. The central mechanism to explain these complex issues has been found.
I am hardly the first to hail this new field of biology as revolutionary—the fundamental process by which nature and nurture interact. But to me, as an anthropologist long trying to take a middle road in a scientific discipline intractably immersed in nature-versus-nurture warfare, epigenetics is the missing link.
FLOCKING BEHAVIOR IN BIRDS
JOHN NAUGHTON
Newspaper columnist; vice-president, Wolfson College, Cambridge; author, From Gutenberg to Zuckerberg: What You Really Need to Know About the Internet
My favorite explanation is Craig Reynolds’s suggestion (first published in 1987) that flocking behavior in birds can be explained by assuming that each bird follows three simple rules: separation (don’t crowd your neighbors), alignment (steer toward the average heading of your neighbors), and cohesion (steer toward the average position of your neighbors).* That such complex behavior can be accounted for in such a breathtakingly simple way is, well, just beautiful.
LEMONS ARE FAST
BARRY C. SMITH
Professor & director, Institute of Philosophy, School of Advanced Study, University of London; author, Questions of Taste: The Philosophy of Wine
When asked to put lemons on a scale between fast and slow, almost everyone says “fast,” and we have no idea why. Maybe human brains are just built to respond that way. Probably. But how does that help? It’s an explanation of sorts but it seems to be a stopping point, when we wanted to know more. This leads us to ask what we want from an explanation: one that’s right, or one that satisfies us? Things that were once self-evident are now known to be false. A straight line is obviously the shortest distance between two points until we think that space is curved. What satisfies our way of thinking need not reflect reality. Why expect a simple theory of a complex world?
Wittgenstein had interesting things to say about what we want from explanations, and he knew different sorts could serve. Sometimes we just need more information; sometimes we need to examine a mechanism, like a valve or a pulley, to understand how it works; sometimes what we need is a way of seeing something familiar in a new light to see it as it really is. He also knew there were times when explanations won’t do: “For someone worried by love, an explanatory hypothesis will not help much.”*
So, what of the near-universal response to the seemingly meaningless question of whether lemons are fast or slow? To be told that our brains are simply built to respond that way doesn’t satisfy us. But it’s precisely when an explanation leaves us short that it spurs us to greater effort; it’s the start of the story, not the end. For the obvious next question to ask is why are human brains built this way? What purpose could it serve? And here the phenomenon of automatic associations may give us a deep clue about the way the mind works, because it’s symptomatic of what we call cross-modal correspondences: non-arbitrary associations between features in one sense modality with features in another.
There are cross-modal correspondences between taste and shape, between sound and vision, and between hearing and smell, many of which are being investigated by experimental psychologist Charles Spence and philosopher Ophelia Deroy. These unexpected connections are reliable and shared—unlike those in cases of synesthesia, which are idiosyncratic, though individually consistent. And the reason we make these connections in the brain is to give us multiple fixes on objects in the environment that we can both hear and see. It also allows us to communicate elusive aspects of our experience.
We often say that tastes are hard to describe, but when we realize that we can change vocabulary and talk about a taste as round or sharp, new possibilities open up. Musical notes are high or low; sour tastes are high, and bitter notes low. Smells can have low notes and high notes. You can feel low, or be incredibly high. This switching of vocabularies allows us to utilize well-understood sensory modalities to map various possibilities of experience.
Advertisers know this intuitively and exploit cross-modal correspondences between abstract shapes and particular products, or between sounds and sights. Angular shapes conjure up carbonated water, not still—whereas an ice cream called “Frisch” would be thought creamier than one called “Frosch.” Notice, too, how many successful companies have names starting with the “K” sound, and how few with “S”. These associations set up expectations in the mind that not only help us perceive but may shape our experiences.
And it’s not just the vocabularies we use. In his 19th-century tract on the psychology of architecture, Heinrich Wolfflin tells us that it’s because we have bodies and are subject to gravity, bending, and balance that we can appreciate the shape of buildings and columns by feeling an empathy for their weight and strain. Physical forms possess a character only because we possess a body.
This idea has led to recent insights into aesthetic appreciation in the work of Chris McManus at University College London. Like all good explanations, it spawns more explanations and further insights. It’s another example of how we use the interaction of sensory information to understand and respond to the world around us. So the fact that we all think lemons are fast may be a big part of the reason we’re so smart.
FALLING INTO PLACE: ENTROPY AND THE DESPERATE INGENUITY OF LIFE
JOHN TOOBY
Founder of evolutionary psychology; codirector, University of California–Santa Barbara Center for Evolutionary Psychology
The hardest choice I had to make in my early scientific life was whether to give up the beautiful puzzles of quantum mechanics, nonlocality, and cosmology for something equally arresting: to work instead on reverse-engineering the code that natural selection built into the programs that make up our species’ circuit architecture. In 1970, the surrounding cultural frenzy and geopolitics made first steps toward a nonideological and computational understanding of our evolved design, “human nature,” seem urgent. The recent rise of computer science and cybernetics made it seem possible. The almost complete avoidance of, and hostility to, evolutionary biology by behavioral and social scientists that had nearly neutered those fields made it seem necessary.
What finally pulled me over was that the theory of natural selection was itself such an extraordinarily beautiful and elegant inference engine. Wearing its theoretical lenses was a permanent revelation, populating the mind with chains of deductions that raced like crystal lattices through supersaturated solutions. Even better, it starts from first principles (such as set theory and physics), so much of it is non-optional.
But still, from the vantage point of physics, beneath natural selection there remained a deep problem in search of an explanation: The world given to us by physics is unrelievedly bleak. It blasts us when it is not burning us or invisibly grinding our cells and macromolecules until we are dead. It wipes out planets, habitats, labors, those we love, ourselves. Gamma-ray bursts wipe out entire galactic regions; supernovae, asteroid impacts, supervolcanos, and ice ages devastate ecosystems and end species. Epidemics, strokes, blunt-force trauma, oxidative damage, protein cross-l
inking, thermal-noise-scrambled DNA—all are random movements away from the narrowly organized set of states that we value, into increasing disorder. The second law of thermodynamics is the recognition that physical systems tend to move toward more probable states, and in so doing tend to move away from less probable states (organization) on their blind toboggan ride toward maximum disorder.
Entropy, then, poses the problem: How are living things at all compatible with a physical world governed by entropy, and, given entropy, how can natural selection lead, over the long run, to the increasing accumulation of functional organization in living things? Living things stand out as an extraordinary departure from the physically normal (for example, the Earth’s metal core, lunar craters, or the solar wind). What sets all organisms—from blackthorn and alder to egrets and otters—apart from everything else in the universe is that woven through their designs are staggeringly unlikely arrays of finely tuned interrelationships—a high order that is highly functional. Yet as highly ordered physical systems, organisms should tend to slide rapidly back toward a state of maximum disorder or maximum probability. As the physicist Erwin Schrödinger put it, “It is by avoiding the rapid decay into the inert state of ‘equilibrium’ that an organism appears so enigmatic.”*
The quick answer, normally palmed off on creationists, is true as far as it goes, but far from complete: The Earth is not a closed system; organisms are not closed systems, so entropy still increases globally (consistent with the second law of thermodynamics) while (sometimes) decreasing locally in organisms. This permits, but does not explain, the high levels of organization found in life. Natural selection, however, can (correctly) be invoked to explain order in organisms, including the entropy-delaying adaptations that keep us from oxidizing immediately into a puff of ash.
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