The oasis

I've always thought it was astonishing that anything short of extremely cold-adapted species could make it through an ice age.

During the last major glacial period, which peaked about twenty-one thousand years ago, the spot where I'm sitting right now was under a thirty-meter-thick layer of ice.  In fact, the hills about fifty kilometers south of us -- the Elmira Moraine -- marks the terminus of the glacier, where rocks, gravel, and soil that had been pushed forward by the advancing ice sheet got left behind as it melted.  During this period, the average global temperature was 6 C colder than it is now, and so much water was locked up as ice that the sea level was over a hundred meters lower than it is today.

My picture of how species survived (excluding the aforementioned cold-lovers) was that everything shifted range toward lower latitudes as the temperature cooled and the ice advanced, then reversed the process as the glacial period ended and the ice receded.  Species that couldn't shift quickly enough, or for which the climatic changes happened too fast to adapt, became extinct.  But according to a paper last week in Science Advances, the picture may not have been quite so simple.

One clue that our understanding was incomplete had to do with genetic diversity.  For a lot of species, we have a pretty good understanding of how quickly genetic mutations accrue, so looking at the genetic makeup of various populations within a species gives you an estimate of how long ago they had a common ancestor.  (And also tells you how closely each of those populations are related to the others.)  And in Europe, the populations of warmth-loving tree species like oaks suggested strongly that modern individuals weren't all descended from southern survivors which gradually expanded their ranges back northward as the glacial period ended twenty-odd-thousand years ago.  Their genetic diversity was too high for that to be plausible -- and some of the northern populations of modern oaks seemed to be a genetic cluster only distantly related to their southern cousins.

Fossils from the Czech Republic strongly suggest that what happened was that patches of the original forest were able to survive, clustered around hot springs that even at the height of the glacial period never froze over.  Geologist Jan Hošek of the Czech Geological Survey, who was lead author of the paper, found fossils of warmth-loving tree species preserved in geyserite -- a sedimentary rock produces by hot water dissolving and then depositing layers of opaline silica on exposed surfaces.  The hot springs created an oasis covering an estimated fifty square kilometers.  Not huge, but enough that a population of oaks and other temperate woodland plants (and presumably the animals they hosted) were able to survive the worst of the cold.

Artist's conception of the hot spring refugium [Image credit: artist Jiří Svoboda]

Being a warmth-lover myself, I always find it astonishing that species made it through some of these climatic extremes.  Not only the cold ones, of course; episodes like the Paleocene-Eocene Thermal Maximum, when the global temperature was 8 C above what it is now, can't have been pleasant, either.  But the recent discoveries show that given even a small refuge, living things will hang on despite all odds.

As Ian Malcolm famously put it, "Life, uh, finds a way."

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Inside the bubble

A couple of nights ago, my wife and I watched the latest episode in the current series of Doctor Who, "Dot and Bubble."  [Nota bene: this post will contain spoilers -- if you intend to watch it, you should do so first, then come back and read this afterward.]

All I'd heard about it before watching is that it is "really disturbing."  That's putting it mildly.  Mind you, there's no gore; even the monsters are no worse than the usual Doctor Who fare.  But the social commentary it makes puts it up there with episodes like "Midnight," "Cold Blood," and "The Almost People" for leaving you shaken and a little sick inside.

The story focuses on the character of Lindy, brilliantly played by Callie Cooke, who is one of the residents of "Finetime."  Finetime is basically a gated summer camp for spoiled rich kids, where they do some nominal work for two hours a day and spend the rest of the time playing.  Each of the residents is surrounded, just about every waking moment, by a virtual-reality shell showing all their online friends -- the "bubble" of the title -- and the "work" each of them does is mostly to keep their bubbles fully charged so they don't miss anything.

The tension starts to ramp up when the Doctor and his companion, Ruby Sunday, show up unannounced in Lindy's bubble, warning her that people in Finetime are disappearing.  At first she doesn't believe it, but when forced to look people up, she notices an abnormal number of them are offline -- she hadn't noticed because the only ones she sees are the ones who are online, so she wasn't aware how many people in her bubble had vanished.  At first she's dismissive of Ruby and downright rude to the Doctor, but eventually is driven to the realization that there are monsters eating the inhabitants of Finetime one by one.

Reluctantly accepting guidance from the Doctor, she runs for one of the conduits that pass under the city, which will give her a way out of the boundaries into the "Wild Wood," the untamed forests outside the barrier.  Along the way, though, we begin to see that Lindy isn't quite the vapid innocent we took her for at first.  She coldly and unhesitatingly sacrifices the life of a young man who had tried to help her in order to save her own; when she finds out that the monsters had already killed everyone in her home world, including her own mother, she basically shrugs her shoulders, concluding that since they were in a "happier place" it was all just hunky-dory.

It was the end, though, that was a sucker punch I never saw coming.  When she finally meets up with the Doctor and Ruby in person, and the Doctor tells her (and a few other survivors) that they have zero chance of surviving in the Wild Wood without his help, she blithely rejects his offer.

"We can't travel with you," she says, looking at him as if he were subhuman.  "You, sir, are not one of us.  You were kind -- although it was your duty to save me.  Screen-to-screen contact is just about acceptable.  But in person?  That's impossible."

In forty-five minutes, a character who started out seeming simply spoiled, empty-headed, and shallow moved into the territory of "amoral" and finally into outright evil.  That this transformation was so convincing is, once again, due to Callie Cooke's amazing portrayal.

What has stuck with me, though, and the reason I'm writing about it today, is that the morning after I watched it, I took a look at a few online reviews of the episode.  They were pretty uniformly positive (and just about everyone agreed that it was disturbing as hell), but what is fascinating -- and more than a little disturbing in its own right -- is the difference between the reactions of the reviewers who are White and the ones who are Black.

Across the board, the White reviewers thought the take-home message of "Dot and Bubble" is "social media = bad."  Or, at least, social media addiction = bad.  If so, the moral to the story is (to quote Seán Ferrick of the YouTube channel WhoCulture) "as subtle as a brick to the face."  The racism implicit in Lindy's rejection of the Doctor was a shocking twist at the end, adding another layer of yuck to an already awful character.

The Black reviewers?  They were unanimous that the main theme throughout the story is racism (even though race was never once mentioned explicitly by any of the characters).  In the very first scene, it was blatantly obvious to them that every last one of Lindy's online friends is White -- many of them almost stereotypically so.  Unlike the White reviewers, the Black reviewers saw the ending coming from a mile off.  Many of them spoke of having dealt all their lives with sneering, race-based microaggressions -- like Lindy's being willing at least to talk to Ruby (who is White) while rejecting the Doctor (who is Black) out of hand.

When considering "Dot and Bubble," it's easy to stop at it being a rather ham-handed commentary on social media, but really, it's about echo chambers.  Surround yourself for long enough with people who think like you, act like you, and look like you, and you start to believe the people who don't share those characteristics are less than you.

What disturbs me the worst is that I didn't see the obvious clues that writer Russell T. Davies left us, either.  When Lindy listens to Ruby and rejects the Doctor, it honestly didn't occur to me that the reason could be the color of his skin.  I didn't even notice that all Lindy's friends were White.  As a result, the ending completely caught me off guard.  As far as the subtle (and not-so-subtle) racist overtones of the characters in the episode, I wasn't even aware of them except in retrospect.

But that's one of the hallmarks of privilege, isn't it?  You're not aware of it because you don't have to be.  As a White male, there are issues of safety, security, and acceptance I never even have to think about.  So I guess like Lindy and the other residents of Finetime, I also live in my own bubble, surrounded by people who (mostly) think like I do, never having to stretch myself to consider, "What would it be like if I was standing where they are?"

And what makes the character of Lindy so horrific is that even offered the opportunity to do that -- to step outside of her bubble and broaden her mind a little -- she rejects it.  Even if it means losing the aid of the one person who is able to help her, and without whose assistance she is very likely not to survive.

For myself, my initial blindness to what "Dot and Bubble" was saying was a chilling reminder to keep pushing my own boundaries.  In the end, all I can do is what poet Maya Angelou tells us: "Do the best you can until you know better.  Then, when you know better, do better."

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The emperor of books

In my novel The Scattering Winds, set seven hundred years in the future, an inquisitive and adventurous young man stumbles upon a relic of the distant past -- a library that somehow survived the cataclysms of our own time, and all the vagaries of circumstance in the following seven centuries.  When he starts going through the treasure-trove of books that have survived, he's struck by the tragic and devastating fact that what was preserved and what was lost was merely a matter of luck, and that for every precious title still in existence, there were a hundred others for which every copy had been destroyed forever.

My inspiration for writing this was that this is, honestly, the situation we're already in.  The vast majority of works from the ancient world are long gone, lost through violence, mishap, and the fact that before the invention of the printing press, making additional copies of books was a long and arduous process, so many of them only ever existed in the form of a copy or two in some monastic library somewhere.  We extol the works of authors like Sophocles and Euripides, but it bears keeping in mind that most of their writing no longer exists.  Our understanding of their work is as fragmentary as if we tried to comprehend the depth and breadth of Shakespeare using only five randomly chosen sonnets, Timon of Athens, and The Merry Wives of Windsor.

It's curious, though, how sometimes circumstances conspire to allow a work to survive.  This is the subject of Stephen Greenblatt's wonderful book The Swerve, looking at how sheer luck resulted in the rediscovery of the single extant copy of the first century B.C.E. philosopher Lucretius's poem De Rerum Natura (On the Nature of Things), the concepts of which were pivotal to the development of science during the Renaissance.  There's another example of this phenomenon, though, which I wonder if you've heard of.  Just about everything we know about the fifth century C.E. turmoil, which resulted in the collapse of the Western Roman Empire and the near-collapse of the Eastern one, is due to the efforts of a single man -- Emperor Constantine VII Porphyrogenitus of Byzantium, who reigned from 913 to 959.

Constantine was the son of Emperor Leo VI "the Wise" and his mistress, Zoë Karbonopsina ("Zoë of the Coal-Black Eyes"), and so he was "born to the royal purple" (that's what his mouthful of a sobriquet means).  When his mother gave birth to him, she insisted on doing so in the Purple Room of the Imperial Palace to emphasize his royal-purple origins in fact as well as symbolically.

Constantine was one of those people who probably shouldn't ever have been involved in politics.  He had a reputation for being smart, honest, generous, and kind, which certainly wasn't (and isn't) a combination that does all that well in office.  He was far more interested in history than he was in administration (a leaning I definitely understand), but was fortunate to have capable ministers who took care of most of the duties of office for him.  All in all, his reign went far better than other times there's been a bookish scholarly type on the throne.  King Henry VI of England comes to mind -- during whose chaotic reign the English got their asses handed to them repeatedly in wars with the French, and the War of the Roses broke out on the home island.

That Constantine fared better is largely due to his smart choices of helpers.  Fortunately for us, because this left him free to pursue his passion, which was saving old manuscripts.  He realized how much of the work of ancient writers had been lost in the paroxysms of the fifth and sixth centuries, so he set about pulling together and recopying everything he could find of what was left. 

[Image licensed under the Creative Commons Wooofer, Constantine VII Porphyrogenitus (2), CC BY-SA 4.0]

The result was a 53-volume set called Excerpta Historica, which contained everything from fragments to whole books by hundreds of ancient authors, some of whom have no other surviving works.  These include Polybius, Nicolaus of Damascus, Dexippus, Eunapius, Peter the Patrician, Menander the Protector, John of Antioch, Thucydides, Xenophon, Diodorus of Sicily, Dionysius of Halicarnassus, Josephus, Arrian of Nicomedia, Iamblichus, Appian of Alexandria, Cassius Dio, Socrates of Constantinople, Theodoret of Cyrrhus, Sozomen, Philostorgius, Procopius, Agathias of Myrina, Theophylact Simocatta, John Malalas and Malchus of Philadelphia.

To name a few.

Two of the historians that Constantine included were Priscus and Zosimus, who lived in Constantinople in the fifth and early sixth centuries (respectively), and from whose writings we know as much as we do about the events leading up to the fall of the Roman Empire.  Imagine it -- without Constantine's preservation of these two writers' histories, we might only know that there had been this huge empire surrounding the Mediterranean, and then... something mysterious happened, and it collapsed.

It does leave you wondering, though, what other major events in history we know nothing about, because any records chronicling them have been lost over the years.  The sad fact is that the depredations of time in the last thousand years continued after Constantine's death, and even of his original 53 volumes, we only have four left -- we only know of the 49 lost volumes from references in other works, and can only speculate about what we might have learned from them.

But at least we have the four that survived.  Without the work of a brilliant, book-loving Byzantine emperor, our knowledge of the ancient history of Europe would be even more incomplete than it is.  And like my main character in The Scattering Winds, from these fragments we can get at least a glimpse into a long-gone world that otherwise we'd know almost nothing about.

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The migrants

Most people know of at least two reasons that organisms can evolve.  The first, of course, is natural selection; members of the same species with inheritable differences can have different survival rates or reproductive rates, leading to overall shifts in the genetic makeup of the population.  The second is catastrophe; a major external event, such as the eruption of the Siberian Traps or the collision of the Chicxulub Meteorite, can completely destabilize what had been a thriving ecosystem, and cause the selective pressures to go off in a completely different direction.  (The two I mentioned were the dominant factors in the Permian-Triassic and Cretaceous-Tertiary extinctions, respectively.)

Less well-known is the role that plate tectonics can play.  When two land masses split apart, the organisms then go their separate ways evolutionarily, especially once the two pieces drift far enough away from each other to experience significantly different climates.  This is what happened to Australia, which most recently was connected to Antarctica; once they diverged, Australia moved northward and Antarctica southward, resulting in just about everything in Antarctica becoming extinct as the temperatures dropped, and leaving Australia with its unique assemblage of species.

The opposite can happen when two continents run into each other.  This occurred when India separated from Africa and collided with Asia, about fifty million years ago, carrying with it species from the southern supercontinent (Gondwana) and introducing them to the northern one (Laurasia).  But an even more striking example occurred when North and South America got close enough that a bit of the seafloor was pushed above water, creating the Isthmus of Panama.

When this happened, on the order of three million years ago, it opened up an easy avenue of two-way migration between the two continents.  This reconnected land masses that had been separated since the breakup of Pangaea in the early Triassic Period, on the order of two hundred million years ago.  That's a long time for species assemblages to evolve in their own directions, and the result was two entirely different floras and faunas.  Those began to move back and forth across the gap as soon as the isthmus formed.

What is curious -- and still largely unexplained -- is why the survival rates of the northward and southward migrants were so drastically different.  Species went both directions; that much is clear from the fossil record.  But just looking at mammals, South America gained (and still has) various species of cats, wolves, foxes, peccaries, deer, skunks, bears, and mice that it gained from North America, to name only a few of the groups that moved in and thrived.  But going the other direction?

There were only three survivors.  The opossum, the armadillo, and the porcupine are the only mammalian South American imports we still have around today.  Others that attempted the northward trek, including ground sloths, glyptodonts, "terror birds," sparassodonts, notungulates, and litopterns, struggled along for a while but eventually became extinct.

[Image is in the Public Domain]

The surmise is that moving from wet forests where it's warm year-round into cooler, drier temperate deciduous forests or grasslands is harder than the reverse, just from the perspective of resources.  Whatever the reason, though, it altered the ecosystems of South America forever, as the North American species proved to be better competitors (and predators), driving entire families of South American mammals extinct.  Some groups continued to thrive and diversify, of course.  Hummingbirds come to mind; they're a distinctly South American group. increasing in diversity as you head south.  Where I live, there's a grand total of one species of hummingbird (the Ruby-throated Hummingbird).

The little country of Ecuador has 132.

The reason all this comes up is the discovery of the complete skeleton of an extinct species of porcupine in Florida, dating to 2.5 million years ago -- and therefore, one of those early migrants northward from its ancestral homeland.  It's related to the modern North American species, but definitely not the same; the extinct species, for example, had a prehensile tail, similar to modern South American species (and which our North American porcupines lack).  It's still unknown, however, if the Florida species is ancestral to our current North American porcupines, or if they're cousins; further study of the skeleton may help to resolve that question.

It's fascinating, though, to see the fingerprints of this mass migration that was to change so radically two different continents.  The process of plate movement continues; Australia will eventually collide with Asia, for example, with similar results, mixing together two sets of species that have been isolated for millions of years.  Change is inevitable in the natural world; it can happen quickly or slowly, and sometimes occurs in ways we're just beginning to understand.

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The tale of a troublemaker

One of the things that resonates about the best fiction is its ability to point us in the direction of truths that somehow transcend the mundane factual reality that surrounds us every day.  I know that there are books that have changed my life and my worldview permanently, twisting my perception around and leaving me fundamentally altered afterward.  The Bridge of San Luis Rey by Thornton Wilder.  A Wrinkle in Time by Madeleine L'Engle.  Foucault's Pendulum by Umberto Eco.  The Lathe of Heaven by Ursula LeGuin.  1Q84 by Haruki Murakami.

These kinds of books may not come along often, but when they do, they can leave you reeling.  As science fiction writer Samuel R. Delany put it, "Fiction isn't just thinking about the world out there.  It's also thinking about how that world might be -- a particularly important exercise for those who are oppressed, because if they're going to change the world we live in, they -- and all of us -- have to be able to think about a world that works differently."

This quote immediately came to mind when I read the new book by Andrew Butters (that I was privileged enough to have a copy of prior to release), Known Order Girls.

The story's protagonist is Katherine Webb, a teenage girl who has grown up as part of the "Known Order" -- a programmed society where everything is run by a sentient AI called Commander.  Commander is the ostensibly benevolent dictator that keeps everything stable, making sure the trains are on time and the economy hums along -- and that each man, woman, and child knows exactly what their place is.

And stays there.

But Katherine is too smart for her own good, and sees that the rules that keep the society stable are also a straitjacket to creativity and growth and individuality.  So she starts to rebel -- in small ways, at first.  The penalties for breaking the Known Order are dramatic and terrifying.  But soon she finds out that the price for compliance might be higher still.

I can honestly say that I have seldom met a protagonist whom I was so invested in, whom I so deeply wanted to win the day.  I won't spoil the story by giving you any details other than a suggestion that there are points you'll want to have plenty of tissues handy.  Stories with teenage main characters are usually targeted toward the Young Adult market, but this is a novel that can (and should) be read by all ages.

In an interesting synchronicity, while I was making dinner yesterday evening, I had my iTunes going, and the wonderful song "I Was Born" by Hanson popped up.

The lyrics immediately put me in mind of Katherine Webb's fight against the monolithic control of Commander.  Sometimes there are people who are born to go places no one's ever gone, do something no one's ever done, and be someone no one's ever been; after reading Known Order Girls, I think you'll agree that Katherine is one of those.

This story is one of those infrequent deeply moving, wildly inspiring tales, reminding us that one determined, defiant troublemaker can indeed change the world for the better.

Do yourself a favor.  Get yourself a copy of Known Order Girls by Andrew Butters.  I promise you won't regret it.

Better still, buy a copy for every teenager you know.  There are features of our own Known Order that could use some defiance right about now.

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Ghost shortage

I sometimes get grief from readers because of my tendency to dismiss claims of the paranormal.

In my own defense, I am convincible.  It just takes more than personal anecdote and eyewitness accounts to do it.  Our memories and sensory-perceptive apparatus are simply not accurate enough recording devices to be relied on for anything requiring scientific rigor.  I find myself agreeing with the hard-nosed skeptic MacPhee in C. S. Lewis's novel That Hideous Strength:

"My uncle, Dr. Duncanson," said MacPhee, "whose name may be familiar to you — he was Moderator of the General Assembly over the water, in Scotland — used to say, 'Show it to me in the word of God.'  And then he’d slap the big Bible on the table.  It was a way he had of shutting up people that came to him blathering about religious experiences.  And granting his premises, he was quite right.  I don’t hold his views, Mrs. Studdock, you understand, but I work on the same principles.  If anything wants Andrew MacPhee to believe in its existence, I’ll be obliged if it will present itself in full daylight, with a sufficient number of witnesses present, and not get shy if you hold up a camera or a thermometer."

So it's not that I'm rejecting anything out of hand, nor saying that your story of seeing your Great Aunt Mildred's ghost fluttering about in your attic last week isn't true.  What I'm saying is that thus far, I personally don't have enough evidence to support a belief in ghosts.  Neither the attempts at rigorous study I've seen, nor my own individual experience, would be at all convincing to someone who didn't already have their mind made up.

And, if you believe an article I just ran across yesterday, any opportunities I might have for changing my opinion are waning fast.

According to paranormal researcher/nuclear physicist Paul Lee, the United Kingdom is "running out of ghosts."  Lee, author of The Ghosts of King's Lynn and West Norfolk, has been tracking paranormal activity in Britain since January 2020, and has seen a marked decline in reports.  "I've been contacting all the reportedly haunted locations on my app, and asking if the residents, owners or staff have experienced any unexplained activity," Lee said.  "So far I've had almost eight hundred replies, and even some supposedly highly haunted places like Conisbrough Castle in South Yorkshire, the Ettington Park Hotel in Stratford -- said to be one of the most haunted hotels in the UK -- and Fortnum and Mason in Piccadilly, say they haven't experienced anything in the last few years."

[Image licensed under the Creative Commons Gallowglass, Medieval ghost, CC BY-SA 3.0]

As far as what's happened to all these spirits, Lee says they may have "moved on."  I guess, like in The Good Place, anything gets boring after a while, and after a few centuries of scaring the shit out of tourists, the ghosts are probably eager for a change of venue.  On the other hand, Lee cautions, just because a particular ghost hasn't been heard from in a while doesn't mean it's gone permanently.  "It may be that ghosts can be recharged," he said.  "You sometimes hear stories of ghosts suddenly reappearing again after many years' absence."

So it could be that this is just a temporary lull, and the ghosts will all come back at some point.  Maybe when the Tories get voted out.

But you have to wonder, of course, if there's something more rational going on here, like the fact that people are wising up to how easy it is to slip into superstition and credulity, and attribute every creaking floorboard to the tread of a spectral foot.  While there are groups that approach these sorts of phenomena the right way (the Society for Psychical Research comes to mind), there are so many more that look at claims of hauntings as a way of turning a quick buck that maybe people are just getting fed up.  Shows like Ghost Hunters can't have helped; week after week, they go to supposedly haunted sites, wander around brushing aside cobwebs and waving their flashlights about in an atmospheric fashion, and like Monty Python's Camel Spotters, every week find conclusive evidence of nearly one ghost.  Despite a zero percent success rate, they always high-five each other for a job well done at the end of the episode, counting on the fact that viewers will already have forgotten that they'd just spent forty-five minutes watching nothing happening.

So maybe there are fewer ghost reports because people are getting smarter about what actually constitutes something worth investigating.  Wouldn't that be nice?

Anyhow, I wish Paul Lee the best of luck.  If the sightings don't pick up, he'll have to go back to nuclear physics to make ends meet, and that would be a damn shame.  And to reiterate my first point, it's not that I'm saying what he claims is impossible; no one would be happier than me if there turned out to be an afterlife, preferably on the beach and involving hammocks, sunshine, the minimum legally-allowable amount of clothing, and drinks with cheerful little paper umbrellas.

In the interim, however, I'll keep looking for hard evidence.  And if tonight I get visited by the spirit of your Great Aunt Mildred and she gives me a stern talking-to, I guess it will serve me right.

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Flocking together

One of the most mesmerizing sights in nature is the collective motion of large groups of animals.

I remember watching films by Jacques Cousteau as a kid, and being fascinated by his underwater footage of schools of fish swimming along and then turning as one, the light flickering from their silvery sides as if they were each reflective scales on a giant single organism.  Murmurations of starlings barely even look real; the flocks swirl and flow like some kind of weird, airborne fluid.  But the most astonishing example of collective motion I've ever seen was when Carol and I visited Bosque del Apache Wildlife Refuge, in central New Mexico, a few years ago, during the migration of snow geese through the region.

"Get there early," we were told.  "At least a half-hour before sunrise.  You'll be glad you did."

We arrived just as the light was growing in the eastern sky.  The wetland was full of tens of thousands of snow geese, all moving around in a relaxed sort of fashion, calling softly to each other.  The brightness in the sky grew, and then -- without any warning at all...

... BOOM.

They all exploded into the air, seemingly simultaneously.  We have wondered many times since what the signal was; there was nothing we could discern, no handful of birds that launched first, no change in the vocalizations that a human would interpret as, "Now!"  One moment everything was calm; the next, the air was a hurricane of flapping wings.  They whirled around, circling higher and higher, and within ten minutes they were all gone, coursing through the sky toward their next destination.

[Image licensed under the Creative Commons CrunchySkies, Snow goose migration at Squaw Creek National Wildlife Refuge, Feb 2013, 25, CC BY-SA 3.0]

How animals manage such feats, moving as a unit without colliding or leaving members behind -- and seemingly without any central coordination -- has long fascinated zoologists.  Way back in 1987, computer simulation expert Craig Reynolds showed (using software called "Boids") that with only a handful of simple rules -- stay within so many wing-lengths of your nearest neighbors but not close enough to touch, match the speed of your neighbors within ten percent either way, steer toward the average heading of your nearest neighbors, give other members a chance to be in any given position in the group -- he was able to create simulated flocking behavior that looked absolutely convincing.  

Last week, a paper out of the Max Planck Gesellschaft showed there's another factor that's important in modeling collective motion, and this has to do with the fact that flying or swimming animals have a rhythm.  Look, for example, at a single fish swimming in an aquarium; its motion forward isn't like a car moving at a steady speed down a highway, but an oscillating swim-glide-swim-glide, giving it a pattern a little like a Slinky moving down a staircase.

Biologist Guy Amichay, who led the research, found that this gives schools of fish a pulse; he compares it to the way we alternate moving our legs while walking.  "Fish are coordinating the timing of their movements with that of their neighbor, and vice versa," Amichay said.  "This two-way rhythmic coupling is an important, but overlooked, force that binds animals in motion.  There's more rhythm to animal movement than you might expect.  In the real world most fish don't swim at fixed speeds, they oscillate."

The key in simulating this behavior is that unlike the factors that Reynolds identified, getting the oscillating movement right depends on neighboring fish doing the opposite of what their nearest neighbors are doing.  The swim-glide pattern in one fish triggers a glide-swim pattern in its friends; put another way, each swim pulse creates a delay in the swim pulse of the school members around it.  

"It's fascinating to see that reciprocity is driving this turn-taking behavior in swimming fish, because it's not always the case in biological oscillators," said study co-author Máté Nagy.  "Fireflies, for example, will synchronize even in one-way interactions.  But for humans, reciprocity comes into play in almost anything we do in pairs, be it dance, or sport, or conversation,"

"We used to think that in a busy group, a fish could be influenced by any other member that it can see," said co-author Iain Couzin. "Now, we see that the most salient bonds could be between partners that choose to rhythmically synchronize."

So zoologists have taken another step toward comprehending one of the most fascinating phenomena in nature; the ability of animals to move together.  Something to think about next time you see a school of fish or a flock of birds in flight.  Getting it right requires rapid and sophisticated coordination we are only now beginning to understand.

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