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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Little cat man

It's amazing how many attempts it took for primates to successfully colonize North America.

There's only one primate species currently in the continent.  Us.  Other mammalian groups -- carnivores, rodents, ungulates, insectivores, bats, and so on -- have done fine here, flourishing and diversifying and lasting for tens of millions of years.

Primates haven't been so successful.

The first primates -- well, proto-primates -- in North America were the plesiadapiformes, which first appear in the fossil record in the early Paleocene Epoch, right after the Chicxulub Impact pretty well wiped out all the big animal species (most notably, the non-avian dinosaurs).  To modern eyes, they would have looked a bit like squirrels:

[Image licensed under the Creative Commons Nobu Tamura (http://spinops.blogspot.com), Plesiadapis NT, CC BY-SA 3.0]

Despite the superficially squirrelly appearance, their skulls, and especially their teeth, show clear affinities with primates, not with rodents.

These guys were widespread, living throughout North America, Europe, and Asia.  All of those continents were still connected at this point -- what had been Pangaea had broken into a northern continent (Laurasia) and a southern continent (Gondwanaland, made up of what are now South America, Australia, and Antarctica).  But things were changing, as they are wont to do.  The Central Atlantic Magmatic Province had kicked into high gear, rifting Laurasia and splitting what would become North America from the rest of the continent, opening up the North Atlantic Ocean.  At that point, the primate species (and everyone else) in North America were pretty well stuck there.

And they lasted a while.  But at the end of the Eocene Epoch, around 34 million years ago, the North American continent got significantly cooler and drier.  This drove all the warmth-loving native primates to extinction.

[Nota bene: South American monkeys come from a different lineage.  Recall that at this point, North and South America were pretty far apart, and there was a lot of ocean in between.  South America was a great deal closer to Africa, though -- and was colonized by primates from Africa, probably by monkeys and other species clinging to rafts of plant roots and brush torn loose during storms.  They seem to have made this amazing journey in several pulses, starting about thirty million years ago.  In any case -- the genetic and structural evidence is clear that South American monkeys are related to primates from Africa, not the extinct groups in North America.]

In any case, North America was primateless for about four million years.  Then, suddenly, a primate appeared in what is now Nebraska.  This species, named Ekgmowechashala (the name is Sioux for "little cat man"), weighed about three kilograms, and looked a bit like a lemur.  But where the hell did it come from?

The whole topic came up in the first place because of new research into this odd creature, which appeared in the Journal of Human Evolution last week.  A thorough analysis of Ekgmowechashala fossils dating from around thirty million years ago found that they most closely resemble primate species in China and eastern Siberia.  Apparently, the ancestors of Ekgmowechashala did what the ancestors of the Native Americans would do, millions of years later.  They took advantage of the fact that the cooler conditions locked up more sea water in the form of ice, lowering sea levels.  Among other things, this turned what is now the Bering Sea into a broad valley with rolling hills (nicknamed Beringia), allowing them to cross into North America.

"The 'Lazarus effect' in paleontology is when we find evidence in the fossil record of animals apparently going extinct -- only to reappear after a long hiatus, seemingly out of nowhere," said Chris Beard, of the University of Kansas, who was senior author of the paper.  "This is the grand pattern of evolution that we see in the fossil record of North American primates. The first primates came to North America about 56 million years ago at the beginning of the Eocene, and they flourished on this continent for more than 20 million years.  But they went extinct when climate became cooler and drier near the Eocene-Oligocene boundary, about 34 million years ago.  Several million years later Ekgmowechashala shows up like a drifting gunslinger in a Western movie, only to be a flash in the pan as far as the long trajectory of evolution is concerned.  After Ekgmowechashala is gone for more than 25 million years, Clovis people come to North America, marking the third chapter of primates on this continent. Like Ekgmowechashala, humans in North America are a prime example of the Lazarus effect."

So the "little cat man" didn't last very long -- the continual cooling of the climate, peaking with the repeated continental glaciations of the "Ice Ages," was more than primates could cope with.  But as Beard points out, that didn't stop our own species from doing the very same thing, eventually colonizing all of North America, and more inhospitable places yet.

But it's odd to think that thirty million years ago, there was something very like a lemur living near what is now Omaha.

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Written in the genes

Two years ago, I wrote about a mysterious plunge in global average temperature that occurred 12,800 years ago.  It's nicknamed the "Younger Dryas event," after the tundra wildflower Dryas octopetala, which showed a population explosion over the following millennium (as judged by pollen in ice core samples).  This plant only flourishes when the winters are extremely cold, and the pollen spike, along with various other lines of evidence, supports a rapid drop in temperature averaging around six degrees Celsius worldwide.

[Image licensed under the Creative Commons xulescu_g, Dryas octopetala (41907904865), CC BY-SA 2.0]

The obvious question, of course, is what could cause such a rapid and catastrophic drop in temperature.  There are three reasonably plausible answers that have been suggested: 

1. an impact by a comet or meteorite causing an ejection of ash into the atmosphere, blocking sunlight
2. the collapse of an ice dam across what is now the St. Lawrence Seaway -- the temperature had been warming prior to the event -- allowing the emptying of an enormous freshwater lake into the North Atlantic, shutting off the thermohaline circulation and propelling the Northern Hemisphere back into an ice age
3. a nearby supernova in the constellation Vela frying the ozone layer, causing a collapse of ecosystems worldwide and an atmospheric chain reaction resulting in a global drop in temperature

The discussion amongst the scientists is ongoing, but the weight of evidence seems to favor the impact hypothesis.  (The link I posted above has more details, if you're curious.)

What's more certain is that the Younger Dryas event had a massive effect.  A number of large mammal groups -- including mastodons, North American camels, dire wolves, and gomphotheres (a bizarre-looking elephant relative) -- all went extinct shortly after the event itself, whatever it was, occurred.  Humans very nearly bit the dust, too; two of the dominant cultures of the time, the Natufian culture of the Middle East and the Clovis culture of North America, both collapsed right around the same time.

It's the latter that brings the topic up, because of some fascinating new research that came out last week, led by Paula Paz Sepúlveda of the Universidad Nacional de La Plata (Argentina), which looks at the effects this wild climate reversal had on the human genome.

What the researchers did was look at the makeup of the Q Y-DNA haplogroup.  You probably already know that two bits of our genome, the Y chromosome and the mitochondrial DNA, are frequently used for analyzing ethnic group affiliations because they don't recombine each generation -- they're passed down intact through (respectively) the paternal and maternal line.  So your mtDNA is the same as your mother's mother's mother's (etc.), and if you're male, your Y DNA is the same as your father's father's father's (etc.).  This means that the only differences in either one are due to mutations, making them invaluable as a measure of the degree of relatedness of different ethnic groups, not to mention providing a way to track patterns of human migration.

The Q haplogroup is ubiquitous in indigenous people of North and South America, so it was a good place to start looking for clues that the climate shift might have written into the human genome.  And they found them; coincident with the Younger Dryas event there was a marked drop in genetic diversity in the Q haplogroup.  It looks like the climate calamity caused a bottleneck -- a severe reduction in population, resulting in a loss of entire genetic lineages:

The YD impact hypothesis states that fragments of a large disintegrating asteroid/comet hit North America, South America, Europe, and Western Asia at 12,800 cal BP.  Multiple airbursts/impacts produced the YD boundary layer (YDB, Younger Dryas boundary), depositing peak concentrations of a wide variety of impact markers.  The proposed impact event caused major changes in continental drainage patterns, ocean circulation, in temperature and precipitation, large-scale biomass burning, abrupt climate change, abrupt anomalous distribution of plants and animals, extinction of megafauna, as well as, cultural changes and human population decline.  The diversity of the set of markers related to the cosmic impact is found mainly in the Northern hemisphere, including Venezuela, but they have also been recorded in the Southern hemisphere, in Chilean Patagonia, and Antarctica.

It's fascinating to think of our own genomes, and (of course) the genomes of other species, as being a kind of proxy record for climate; that not only gradual fluctuations, but sudden and unexpected events like impacts and volcanic eruptions, can leave their marks on our DNA.  It brings home once again how interlocked everything is.  Our old perception of humans as being some kind of independent entity, separate from everything else on Earth, is profoundly wrong.  We were molded into what we are today by the same forces that created the entire biosphere, and we can't separate ourselves from those forces any more than we could disconnect from our own heartbeats.  As Chief Seattle famously put it, "Man did not weave the web of life, he is merely a strand in it.  Whatever he does to the web, he does to himself."

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Mapping out a fraud

Ever heard of the Vinland Map?

Supposedly dating from the fifteenth century, this map shows the outlines of Europe, Greenland, Asia, Africa... and North America, which is labeled "Vinland Insula" (the island of Vinland).  The map surfaced in 1957, and was widely hailed as a genuine depiction of the Norse exploration of northeastern North America, drawn using information gathered as far back as the tenth century C.E.

Interestingly, the map surfaced three years before the discovery of the (authentic) Viking-era archaeological site at L'Anse-aux-Meadows, Newfoundland, the first (and at this point, only) certain Norse site in North America.  When tenth-century Norse artifacts were found there in 1960, it bolstered the claims that the map was genuine.  We know the Vikings made it to "Vinland," as per the stories of Leif Eiriksson and Thorfinn Karlsefni, and the Map seemed to indicate they'd made it a lot farther, possibly to what is now coastal New England and points south.

Very quickly, it became the center of a lot of wilder claims.  Ancient Aliens aficionados said that not only did it show that the Norse had visited North America and surveyed it closely enough to get a lot of the details of the coastline correct, it contained enough information to support that the drawing had been made from a higher vantage point -- i.e., from the air.  In a spaceship.  Because the Norse gods were actually Ancient Astronauts.

Even the less up-in-the-stratosphere claims were given substantial momentum by the Vinland Map.  I remember when I was working on my master's thesis -- about the effects of the Viking invasions on the Old English and Old Gaelic languages -- running into an apparently serious study purporting to find evidence of borrow-words from Old Norse into various Algonkian languages, including Malecite, Abenaki, and Mi'kmaq.  The difficulty with this sort of thing is in determining whether pairs of similar words from otherwise unrelated languages are related genetically (i.e. from a common root) or are just chance correspondences; in fact, that was one of the more difficult parts of my own research.  Sometimes it's obvious, but that's the exception.  An example is the English word window -- the Old English word was eagþyrl and the Norse word at the same time was vindauga.

Doesn't take a linguist to figure that one out.

Most, however, are not that clear-cut, and it takes more evidence than "they sound kind of the same" to establish a genetic connection.  And the vast majority of linguists think that any similarities between Norse words and Algonkian words are chance -- and cherry-picking.  You can find those sorts of accidental correspondences between just about any two languages you pick if you're allowed to ignore all the pairs of words that don't sound alike.

In any case, the Vinland Map was considered support for the contention that the Vikings did get south of L'Anse-aux-Meadows, whether or not they left linguistic and/or archaeological traces.  This claim gained some credence when a physicist tested the parchment of the Map back in 1995 and found that it dated somewhere between 1432 and 1445, exactly as advertised.

Unfortunately, the age of the parchment is irrelevant -- because a study published last week by some researchers at Yale University, where the map is housed, found that beyond question, the Vinland Map is a fake.

The researchers were able to do an analysis of the ink used on the Map without destroying it, and found that it is unquestionably modern ink.  It contains anatase, a form of titanium dioxide first used in inks in the 1920s.  Also, it was discovered that one of the inscriptions on the map had been overwritten to appear as if it was a bookbinder's instructions to assemble the map pages in concordance with the Speculum Historiale, a thirteenth-century encyclopedia intended as a compendium of everything known to the intelligentsia of Europe at the time.

"The Vinland Map is a fake," said Raymond Clemens, curator of early books and manuscripts at Yale’s Beinecke Rare Book and Manuscript Library.  "There is no reasonable doubt here. This new analysis should put the matter to rest...  The altered inscription certainly seems like an attempt to make people believe the map was created at the same time as the Speculum Historiale.  It’s powerful evidence that this is a forgery, not an innocent creation by a third party that was co-opted by someone else, although it doesn’t tell us who perpetrated the deception."

My first response to reading this was to get really pissed off.  Not only does this claim have significant bearing on the subject of my own research, it muddies the waters considerably with respect to any legitimate claims that the Norse reached mainland North America.  Historical linguistics is hard enough; having some asshole create a highly-plausible fake -- good enough that it took sophisticated ink analysis to detect it -- makes it more difficult for those of us who just want to know what really happened.

Fakes in general really make me see red.  We already have the natural biases all humans come equipped with (confirmation bias, correlation/causation errors, and dart-thrower's bias, particularly) gumming up the works even for reputable scientists who are trying their hardest to see things clearly.  It may seem like a minor concern -- who really cares if a particular old document is genuine?  But truth matters, even if it's an argument about what might seem like academic trivia.

Or it should matter.  What's most troubling about this is that whoever created the Vinland Map evidently knew what (s)he was doing, and knew the subject well enough to fool historians for over fifty years.  (Well, some historians -- there were researchers who doubted it pretty much from the get-go.)  So the great likelihood is whoever perpetrated this fake was an academic him/herself.

And to me, that's unconscionable.

So that's our disappointing piece of news for the day.  It still seems pretty likely to me that the Norse did make it to mainland North America, but even if I'm right we're back to having zero hard evidence.  I guess I'm lucky that I chose the thesis research I did; there's no doubt the Vikings made it to Britain.  The monks at Lindisfarne would have been happy to tell you all about it.

At least the ones who survived.

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My friends know, as do regular readers of Skeptophilia, that I have a tendency toward swearing.

My prim and proper mom tried for years -- decades, really -- to break me of the habit.  "Bad language indicates you don't have the vocabulary to express yourself properly," she used to tell me.  But after many years, I finally came to the conclusion that there was nothing amiss with my vocabulary.  I simply found that in the right context, a pungent turn of phrase was entirely called for.

It can get away with you, of course, just like any habit.  I recall when I was in graduate school at the University of Washington in the 1980s that my fellow students were some of the hardest-drinking, hardest-partying, hardest-swearing people I've ever known.  (There was nothing wrong with their vocabularies, either.)  I came to find, though, that if every sentence is punctuated by a swear word, they lose their power, becoming no more than a less-appropriate version of "umm" and "uhh" and "like."

Anyhow, for those of you who are also fond of peppering your speech with spicy words, I have a book for you.  Science writer Emma Byrne has written a book called Swearing Is Good for You: The Amazing Science of Bad Language.  In it, you'll read about honest scientific studies that have shown that swearing decreases stress and improves pain tolerance -- and about fall-out-of-your-chair hilarious anecdotes like the chimpanzee who uses American Sign Language to swear at her keeper.

I guess our penchant for the ribald goes back a ways.

It's funny, thought-provoking, and will provide you with good ammunition the next time someone throws "swearing is an indication of low intelligence" at you.  

[Note: if you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!]

Dire straits

During my junior year as an undergraduate, I had to take a humanities elective as part of my degree requirements and settled upon a class in archaeology, a subject which had always been an interest of mine.  The course description sounded pretty cool, and I thought it would be a fun challenge to take on.

However, I had not reckoned with the fact that the professor, one Dr. Servello, seemed to have a screw loose.  I found this out early on when one day he caught a glimpse of some genealogical charts in my binder (part of a family tree project I was doing as an anniversary gift for my parents), and added that to the fact that I wore a St. Christopher medal, and concluded from this that I was a member of a cult.

He kept me after class that day to ask me what my cult believed.  When I protested that in fact, I did not belong to a cult, he became genuinely concerned and said, "No, no, you don't need to be afraid to tell me!  I'm fascinated by alternative belief systems!"

But the most striking thing about Dr. Servello was that he never admitted to being wrong.  About anything.  He had a nearly Trumpian ability to continue arguing his point even after having hard evidence that he'd misspoken thrown into his face.  One time he argued for a half-hour over the correct pronunciation of a Chinese archaeological site -- with a student from China.  In very short order we learned not to bother contradicting him about any of the wacky things he said, because it never accomplished anything but wasting inordinate amounts of class time.

But as in any group, in the class there was That Guy.  He felt duty-bound to challenge Dr. Servello every time he made shit up, which was usually several times per class.  But the one that stands out in my memory was the epic argument that ensued when Dr. Servello was telling us about dire wolves.

"It's one of the largest predatory mammals ever," he said, with great conviction.  "They were fourteen feet tall at the shoulder."

Simultaneously all of the two-dozen-odd students in the class gave Dr. Servello the human equivalent of the Canine Head Tilt of Confusion.  Even so, most of us just added it to our growing list of bizarre Servello-isms, and were prepared to let it go.

But not That Guy.

"That's impossible," he said flatly.

"No, no, they were huge!" Dr. Servello insisted.  "Biggest predatory mammal ever!"

"That's impossible," That Guy said through clenched teeth.  "A wolf that big could look into a second-story window."

There followed a good forty-five minute-long argument, ending with That Guy grabbing his binder and storming out of class.

I related the story to some friends later.  These friends always waited with bated breath for me to come out of archaeology class, to see what lunatic pronouncements Dr. Servello had made that day.  This one, however, was impressive even by comparison to his previous efforts.

"That," one of my friends said reverently, "is one big bow-wow."

The topic comes up because while dire wolves are not fourteen feet high at the shoulder (which, for the record, would make them taller than a full-grown male African elephant) they are a fascinating species.  They were pretty impressive animals -- adults averaged a meter high at the shoulder and a little over two meters from tip to tail -- but their skeletal morphology led taxonomists to believe they were simply larger cousins of the North American gray wolf, descended from a parental species that had crossed the Bering Land Bridge into Eurasia.  But that idea is being challenged by some new analysis of DNA from dire wolves who were trapped in the La Brea Tar Seeps forty-some-odd thousand years ago, and a comparison with gray wolf DNA supports a conclusion that the last common ancestry of the two species was around 5.7 million years ago, before the ancestors of today's gray wolves had crossed into North America.

Dire wolf skeleton in the Sternberg Museum, Hays, Kansas [Image licensed under the Creative Commons James St. John, Canis dirus Sternberg Museum, CC BY 2.0]

The research, which was the subject of a paper in Nature this week, suggests that the morphological similarities between gray wolves and dire wolves are due to convergent evolution -- the evolution of superficially similar traits in distantly-related species that are under the same selective pressures.  And of course, these two were starting out closer in structure anyhow; no one is doubting that dire wolves are canids.  But the DNA difference is striking enough that the researchers are proposing to take the dire wolf out of the genus Canis and place it in its own new genus -- Aenocyon, meaning "terrible wolf."

"These results totally shake up the idea that dire wolves were just bigger cousins of gray wolves," said paleontologist Grant Zazula, who was not involved in the new study, in an interview with Scientific American.  "The study of ancient DNA and proteins from fossil bones is rapidly rewriting the ice age and more recent history of North America’s mammals."

It is not, for the record, rewriting how big they were.  As terrible as Aenocyon was, it wouldn't have towered over an elephant.  However, it is thought to have had the greatest bite force of any canid ever, and as it seems to have been a pack hunter, could take down some of the megaherbivores of its time -- giant ground sloths, North American camels and horses, bison... and even mastodons.

But like most of the Ice Age megafauna, the changing climate at the end of the Pleistocene put the dire wolf in dire straits.  They're thought to have persisted in areas of the northern Rockies as little as 9,500 years ago, but when the big prey animals began to disappear, selection favored their smaller (now thought to be distant) cousins, gray wolves.

Which is kind of a shame.  They were impressive beasts, even if they weren't the big bow-wows Dr. Servello claimed they were.  And it's nice to clarify at least a little more of their genetics and history, turning a lens on a species we thought we understood.

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As a biologist, I've usually thought of myself as immune to being grossed out.  But I have to admit I was a little shocked to find out that the human microbiome -- the collection of bacteria and fungi that live in and on us -- outnumber actual human cells by a factor of ten.

You read that right: if you counted up all the cells in and on the surface of your body, for every one human cell with human DNA, there'd be ten cells of microorganisms, coming from over a thousand different species.

And that's in healthy humans.  This idea that "bacteria = bad" is profoundly wrong; not only do a lot of bacteria perform useful functions, producing products like yogurt, cheese, and the familiar flavor and aroma of chocolate, they directly contribute to good health.  Anyone who has been on an antibiotic long-term knows that wiping out the beneficial bacteria in your gut can lead to some pretty unpleasant side effects; most current treatments for bacterial infections kill the good guys along with the bad, leading to an imbalance in your microbiome that can persist for months afterward.

In The Human Superorganism: How the Microbiome is Revolutionizing the Pursuit of a Healthy Life, microbiologist Rodney Dietert shows how a lot of debilitating diseases, from asthma to allergies to irritable bowel syndrome to the inflammation that is at the root of heart disease, might be attributable to disturbances in the body's microbiome.  His contention is that restoring the normal microbiome should be the first line of treatment for these diseases, not the medications that often throw the microbiome further out of whack.

His book is fascinating and controversial, but his reasoning (and the experimental research he draws upon) is stellar.  If you're interested in health-related topics, you should read The Human Superorganism.  You'll never look at your own body the same way again.

[Note:  if you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!]

Very early Californians

Yesterday's post about self-correction and reframing in science prompted a friend of mine, the phenomenal author, blogger, and all-around polymath Gil Miller, to send me an interesting link about an archaeological site in California.

The striking thing about this link is its alleged age.  There are mastodon bones showing signs of butchering dating to 130,000 years ago -- which is 115,000 years older than the oldest recording human-occupied site in North America.

[Image licensed under the Creative Commons Dantheman9758 at the English Wikipedia, Mastodon+Human, CC BY-SA 3.0]

Accepting this would require a major retooling of our understanding of the human colonization of the continent.  Were there other hominids living here, who then died out prior to the ancestors of the Native Americans crossing her from Asia?  If so, why aren't there more fossils and other relics?  Was this an early wave of colonization from Siberia, which made it to California but ultimately was unsuccessful?  Is the damage to the bones caused by something other than butchering?  Are the dates of the bones in error?

The answer to the last-asked question, at least, seems to be no.  If a site shows anomalous dates, the first thing you do is... check the dates.  Which was done, and it seems like the radioisotope dating of the mastodon bones is correct.

As far as the others, here's what the authors have to say (from their 2017 paper on the topic in Nature).  The passage is a bit long, but it gives you the scope of their argument:

The earliest dispersal of humans into North America is a contentious subject, and proposed early sites are required to meet the following criteria for acceptance: (1) archaeological evidence is found in a clearly defined and undisturbed geologic context; (2) age is determined by reliable radiometric dating; (3) multiple lines of evidence from interdisciplinary studies provide consistent results; and (4) unquestionable artefacts are found in primary context.  Here we describe the Cerutti Mastodon (CM) site, an archaeological site from the early late Pleistocene epoch, where in situ hammerstones and stone anvils occur in spatio-temporal association with fragmentary remains of a single mastodon (Mammut americanum).  The CM site contains spiral-fractured bone and molar fragments, indicating that breakage occured while fresh.  Several of these fragments also preserve evidence of percussion.  The occurrence and distribution of bone, molar and stone refits suggest that breakage occurred at the site of burial.  Five large cobbles (hammerstones and anvils) in the CM bone bed display use-wear and impact marks, and are hydraulically anomalous relative to the low-energy context of the enclosing sandy silt stratum.  230Th/U radiometric analysis of multiple bone specimens using diffusion–adsorption–decay dating models indicates a burial date of 130.7 ± 9.4 thousand years ago.  These findings confirm the presence of an unidentified species of Homo at the CM site during the last interglacial period (MIS 5e; early late Pleistocene), indicating that humans with manual dexterity and the experiential knowledge to use hammerstones and anvils processed mastodon limb bones for marrow extraction and/or raw material for tool production.  Systematic proboscidean bone reduction, evident at the CM site, fits within a broader pattern of Palaeolithic bone percussion technology in Africa, Eurasia, and North America.  The CM site is, to our knowledge, the oldest in situ, well-documented archaeological site in North America and, as such, substantially revises the timing of arrival of Homo into the Americas.

As I discussed yesterday, the process of science is that when someone makes a claim, his/her fellow scientists immediately jump in and tear it apart, looking at it from every angle, asking if there are other explanations that account for all the evidence, and in general trying to refute it.  They don't do this to be mean.  The idea is to see if the proposed model can withstand scrutiny -- to see, in scientific parlance, if it is "robust."

And this claim had an additional caveat; to accept it meant to undo our entire previous understanding of how the Americas were colonized by humans.  Carl Sagan's "ECREE Principle" applies here -- "Extraordinary Claims Require Extraordinary Evidence."  So the cross-checking and verification was especially intense.

Most archaeologists were unconvinced.  In an article in BBC Online by BBC science editor Paul Rincon, David Meltzer, professor of archaeology at the Southern Methodist University of Dallas, Texas, put it most succinctly: "Nature is mischievous and can break bones and modify stones in a myriad of ways.  With evidence as inherently ambiguous as the broken bones and nondescript broken stones described in the paper, it is not enough to demonstrate they could have been broken/modified by humans; one has to demonstrate they could not have been broken by nature.  This is an equifinality problem: multiple processes can cause the same product."

Which is the problem in all of science.  In order to demonstrate your claim, you have not only to provide evidence, but to show that there is no other explanation that explains it equally well.  Especially here, when to accept the claim requires rewriting everything we know about Western Hemisphere archaeology -- invoking another good rule of thumb, Ockham's Razor.

Usually framed as, "if there are competing explanations, the one that requires the fewest ad hoc assumptions is most likely to be correct."

So at the moment, the consensus about the Cerutti Mastondon Site claim is "maybe, but probably not."  The Holen et al. paper has not stood the test of scientific scrutiny.  Which doesn't mean the claim is wrong; plenty of weird claims have later been shown, by virtue of additional evidence, to have been correct.  But in the absence of that evidence, we have to be able to say, "We don't know."

As an extraordinary claim, thus far it seems not to have reached the bar of support we expect in science.

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This week's Skeptophilia book of the week is a dark one, but absolutely gripping: the brilliant novelist Haruki Murakami's Underground: The Tokyo Gas Attack and the Japanese Psyche.

Most of you probably know about the sarin attack in the subways of Tokyo in 1995, perpetrated by members of the Aum Shinrikyo cult under the leadership of Shoko Asahara.  Asahara, acting through five Aum members, set off nerve gas containers during rush hour, killing fifty people outright and injuring over a thousand others.  All six of them were hanged in 2018 for the crimes, along with a seventh who acted as a getaway driver.

Murakami does an amazing job in recounting the events leading up to the attack, and getting into the psyches of the perpetrators.  Amazingly, most of them were from completely ordinary backgrounds and had no criminal records at all, nor any other signs of the horrors they had planned.  Murakami interviewed commuters who were injured by the poison and also a number of first responders, and draws a grim but fascinating picture of one of the darkest days in Japanese history.

You won't be able to put it down.

[Note: if you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!]

Building the Rockies

I recently re-read John McPhee's wonderful quartet of books on geology, Basin and Range, Rising from the Plains, In Suspect Terrain, and Assembling California.  His lucid prose and capacity for focusing on the human stories connected with the subject while teaching us some fascinating science brought me back to these books, which I first read perhaps twenty years ago.

The first two, in particular, describe something that is quite surprising -- or at least was to me when I first learned about it.  The biggest mountain range in the United States, the Rockies, is actually quite poorly understood, and contains some features that are still yet to be satisfactorily explained.  A good part of the Rocky Mountain range is non-volcanic, and although there are some areas that have igneous rocks the vast majority is made up of sedimentary and metamorphosed sedimentary rock -- sandstone, limestone, shale, slate, quartzite, and marble.  Even some of the igneous rocks only show at the surface because the overlayment of sedimentary rock that once was present has eroded away.

[Image licensed under the Creative Commons Self, Rocky Mountain National Park, CC BY-SA 2.5]

As McPhee describes it, the current thought is that most of what is west of Colorado and Wyoming is probably the result of accretion -- the huge North American Plate overriding smaller plates to the west and gathering up microcontinents and island arcs they carried, cementing them onto the coastline.  It's certain that this is how California formed -- the boundaries between the different "suspect terranes" (the alternate spelling is used when referring to these chunks of land that end up in a very different place from where they were formed) are pretty well established.  Also, the subduction process that brought them to North America is still ongoing, as the small Explorer, Juan de Fuca, and Gorda Plates (in order from north to south) are pulled underneath -- giving rise to the Cascade Volcanoes such as Mount Lassen, Mount Hood, Mount Rainier, and Mount Saint Helens.

We got another piece added to the puzzle with a paper this week in Nature, out of the University of Alberta, by Yunfeng Chen, Yu Jeffrey Gu, Claire A. Currie, Stephen T. Johnston, Shu-Huei Hung, Andrew J. Schaeffer, and Pascal Audet.  Entitled, "Seismic Evidence for a Mantle Suture and Implications for the Origin of the Canadian Cordillera," the paper describes research that found a sharp boundary in the mantle of the Earth between the "craton" -- the central, oldest piece of the North American continent, encompassing what is now the Midwest -- and a long, narrow microcontinent that slammed into the North American Plate as a primordial sea closed -- moving the coastline hundreds of miles further west.

"This research provides new evidence that the Canadian section of this mountain range was formed by two continents colliding," said Jeffrey Gu, professor in the Department of Physics and co-author on the study, in an interview with Science Daily.  "The proposed mechanism for mountain building may not apply to other parts of the Rocky Mountains due to highly variable boundary geometries and characteristics from north to south."

The cool part is that the research was done by looking deep into the Earth's mantle -- not just by studying the surface features.  And this collision, which is estimated to have occurred a hundred million years ago, has left a scar that is still detectable.  "This study highlights how deep Earth images from geophysical methods can help us to understand the evolution of mountains, one of the most magnificent processes of plate tectonics observed at the Earth's surface," said study co-author Yunfeng Chen.

And this technique could be applied elsewhere, as the Rockies are far from the only mountain range in the world that were created by accretion rather than volcanism.  (The obvious examples are the Alps and the Himalayas -- the latter of which are still rising as the Indian Plate continues to plow into the Eurasian Plate.)  "There are other mountain belts around the world where a similar model may apply," said Claire Currie, associate professor of physics and co-author on the study.  "Our data could be important for understanding mountain belts elsewhere, as well as building our understanding of the evolution of western North America."

So we're piecing together the picture of how the Rockies formed -- ironic, as they seem to have been assembled from pieces themselves.  In the process, we're learning more about the processes that move the tectonic plates, and create the landscape we see around us.  It reminds me of the haunting lines from Alfred, Lord Tennyson, which seem like a fitting way to end:

O Earth, what changes hast thou seen?
There where the long road roars has been
The stillness of the central sea;
The hills are shadows, and they flow
From form to form, and nothing stands,
They melt like mists, the solid lands,
Like clouds, they shape themselves, and go.

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Aptly enough, considering Monday's post about deciphering scripts, this week's Skeptophilia book recommendation is Steven Pinker's brilliant The Stuff of Thought.  Here, experimental psychologist Pinker looks at what our use of language tells us about our behavior and neural wiring -- what, in fact, our choice of words has to do with human nature as a whole.

Along the way, he throws out some fascinating examples -- my favorite of which is his section on the syntax of swearing.  I have to admit, the question, "Just what does the 'fuck' in 'fuck you' actually mean?" is something I've never thought about before, although it probably should have given that I'm guilty of using the f-word a lot more than is generally considered acceptable.

So if you're interested in language, the human mind, or both, this is a must-read.  Although I'll warn you -- if you're like me, it'll leave you thinking, "Why did I just say that?" several times a day.