A Cambrian holdout

Although you don't tend to hear much about it, the Ordovician Period was a very peculiar time in Earth's history.

From beginning (485 million years ago) to the end (444 million years ago) it experienced one of the biggest global climatic swings the Earth has ever seen.  In the early Ordovician the climate was a sauna -- an intense greenhouse effect caused the highest temperatures the Paleozoic Era would see, and glacial ice all but vanished.  By the end, the center of the supercontinent of Gondwana was near the South Pole, and glaciers covered much of what is now Africa and South America, resulting in a massive extinction that wiped out an estimated sixty percent of life on Earth.

At this point, life was confined to the oceans.  The first terrestrial plants and fungi wouldn't evolve until something like twenty million years after the beginning of the next period, the Silurian, and land animals only followed after that.  So during the Ordovician, the shift in sea level had an enormous impact -- as the period progressed and more and more ocean water became locked up in the form of glacial ice, much of what had been shallow, temperate seas dried up to form cold, barren deserts.  And that was all there was on land -- thousands of square kilometers of rock, sand, and ice, without a single living thing larger than bacteria to be found anywhere.

Somehow, despite the extreme climatic swings that happened during the Ordovician, life in the oceans diversified, and rebounded after the dramatic dieoff at the end.  And along the way, there were some really peculiar life forms.

One of these was discovered not long ago in the Castle Bank Formation in the middle of Wales.  (Ordovician outcrops in Wales are what gave the period its name; the Ordovices were a tribe that lived there around the time of the Roman conquest of Britain.)  The animal was small -- the fossil measures only thirteen millimeters from tip to tail -- but it was one odd-looking critter:

A reconstruction of Mieridduryn bonniae [Image credit: Franz Anthony]

Aficionados of paleontology will no doubt immediately recognize the similarity to Cambrian animals called Opabinia and Anomalocaris; Mieridduryn looks almost like a hybrid of the two.  (If you're a linguistics geek like myself, you might be interested to know that the genus name Mieridduryn comes from Welsh words meaning "bramble snout.")  And it does seem to be a holdover from the Cambrian Explosion fauna, which also produced such weird forms as Hallucigenia (the name means "comes from a hallucination"), which is so bizarre that at first, paleontologists reconstructed it upside down, until some better-preserved fossils made them realize their error.

[Image licensed under the Creative Commons Qohelet12, Hallucigenia, CC BY-SA 4.0]

By the Ordovician, however, a lot of the stranger (to our eyes, at least) life forms had gone extinct, and the wipeout at the end of the Ordovician finished off the last of them.  At that point, what was left -- arthropods, primitive vertebrates, mollusks, echinoderms, annelids, and so on -- would have begun to look a lot more familiar to us.

But during the mid-Ordovician, when Mieridduryn was snorking about in the mud of shallow, warm oceans, there were still some mighty peculiar animals.  If you hopped a time machine and went back there, you might well think you were on a different planet.  It reminds me of the poem by Irish geologist John Joly, which he was inspired to write while looking at a the fossil of a long-extinct animal, and seems a fitting place to end:

Is nothing left?  Have all things passed thee by?

The stars are not thy stars.  The aged hills

Are changed and bowed beneath the ills

Of ice and rain, of river and sky;

The sea that riseth now in agony

Is not thy sea.  The stormy voice that fills

This gloom with man's remotest sorrow shrills

The memory of thy lost futurity.

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Glimpse of the dawn

A pair of words biologists (and interested laypeople) have to be careful with are primitive and advanced.

They're often used in place of the generally more appropriate simple and complex.  By that usage, an amoeba is primitive and an aardvark is advanced.  But where it gets confusing is that primitive and advanced are also sometimes used to mean "like something that evolved earlier" and "like something that evolved more recently," respectively -- so they use primitive to describe a stegosaurus and advanced to describe a spider monkey, when in fact both of those are about equally complex.  (It gets even murkier when you throw in questions of relative intelligence.)

It bears keeping in mind that while modern organisms vary greatly on the simple/complex spectrum, they all have lineages that have been around exactly the same amount of time -- 4.3 billion years, give or take a day or two.  All known lineages of terrestrial life converge on a single life form nicknamed LUCA -- the Last Universal Common Ancestor -- around four billion years ago.  To our eyes, LUCA probably wouldn't have looked like much.  It probably resembled species we now classify as bacteria.

But all life on Earth descends from it.  And as far as the primitive/advanced bit, the only difference is in that time, some of the lineages changed a great deal more than others did.

The reason this comes up is because of a link sent to me by a friend and frequent contributor of topics for Skeptophilia, about a species of fairly modern-looking jellyfish that was found in rock strata that are 505 million years old.

The species, named Burgessomedua phasmiformis, was a free-swimming, tentacle-laden predator with a bell on the order of twenty centimeters in diameter.  It, like many of the Cambrian explosion fauna, were found in the exceptionally well-preserved Burgess Shale Formation of the Canadian Rockies in British Columbia.

Artist's impression of live Burgessomedusa in the Cambrian seas [courtesy of artist Christian McCall]

Jellyfish and most of the other members of Phylum Cnidaria are generally scarce in the fossil record, because their bodies are primarily water.  If you've ever seen a dried-up jellyfish on the beach, you know what I'm talking about; there's barely anything left.  (Don't assume that this means they're harmless, though.  Even the dried tentacles of a Portuguese man-o'-war can pack a dangerous sting.)  But you can see how astonishing it is not only to have one create an impression in sedimentary rocks, but to have that impression last for 505 million years.

So the exceptional preservation of this extremely rare fossil animal is amazing enough.  But what I find even more mind-boggling when I think about the life back then is the bigger picture of what the Cambrian Period was like.  At that point, all life was in the water.  There was (more or less) the same amount of land as there is now, albeit configured completely differently -- but on that land was not a single living thing.  No plants, no fungi, no animals.  Nothing.  It was a vast expanse of empty rock, sand, and dust.

At this point, the first terrestrial plants wouldn't make their appearance for another fifty million years, and even then, they were highly water-dependent and very likely clustered along shorelines.  The first vascular plant -- one with the internal plumbing most plants have today -- that appears in the fossil record is Cooksonia, which appeared during the mid-Silurian Period (about 430 million years ago).  It was a strange, rather Dr. Seussian thing:

[Image licensed under the Creative Commons Smith609 Ground texture from Image:Mud closeup.jpg, Cooksonia pertoni, CC BY 3.0]

But when Burgessomedusa was swimming in the Cambrian oceans, all that lay millions of years in the future.  This glimpse of the dawn of time gives us a picture so alien to our current mental image of the Earth it's hard to believe it's the same planet.

What this tells paleontologists, though, is that even in the early Cambrian, there were relatively modern-looking jellyfish -- and that even though today's cnidarians are advanced in the sense of "length of their lineage on Earth," they haven't changed much at all during all those hundreds of millions of years.  The general reason for such stability is that the body plan works; there's little selective pressure to favor alterations in a system that does fine as is, however "primitive" it may look to us.

As a writer friend of mine posted yesterday:

The details might be off a little, but the gist is accurate enough.

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An explosion of understanding

One of the reasons I love science is its capacity for inducing wonder.

Albert Einstein said it best: "Joy in looking and comprehending is nature’s most beautiful gift."  Being able to look around you and think, "Okay, now I understand a little bit more of the universe" is nothing short of a thrill.

I recall having that feeling when I first learned about the Cambrian Explosion, a sudden increase in biodiversity that occurred about 540 million years ago, and which produced virtually all the animal phyla we currently have today.  I think it struck me that way because it was so contrary to the picture I'd had, of evolution slowly plodding along, from something like a jellyfish to something like a worm to something like a fish, through amphibians and reptiles and mammals, finally leading to us as (of course) the Pinnacle of Creation.  That view, it seems, is substantially wrong.  While there has been great change on many branches of the family tree of life, all of the basic branches diverged right about the same time.

Fascinating, too, that there were also a variety of branches that left no living descendants, that are so bizarre to our eyes that they look more like something from a science fiction movie.  There's Dickinsonia:

[Image is licensed under the Creative Commons Verisimilus at English Wikipedia, DickinsoniaCostata, CC BY-SA 3.0]

... and Anomalocaris, shown here as a model of what it might have looked like when alive:

[Image is in the Public Domain]

... and the aptly named Hallucigenia, which could be straight out of a fever-dream:

[Image is licensed under the Creative Commons Scorpion451, Hallucigenia Reconstruction Current 2015, CC BY-SA 4.0]

... and my personal favorite, five-eyed, vacuum-cleaner-hose-equipped Opabinia:

[Image is licensed under the Creative Commons Nobu Tamura (http://spinops.blogspot.com), Opabinia BW, CC BY 3.0]

If you'd like to find out more, I encourage you to read Stephen Jay Gould's awesome book Wonderful Life, which will tell you about these four creatures and a great many more besides.

The reason I bring this up is that some research out of Oxford University has elucidated not only the structure of these odd creatures, but the environment in which they lived.  Having fossils from 540 million years ago that were sufficiently intact to determine what they'd looked like while alive is amazing enough; but being able to determine anything about the conditions under which they lived is downright astonishing.  But that's just what Ross Anderson and Nicholas Tosca, of the Department of Sedimentary Geology at Oxford, and their team have done.

Their paper, which appeared in the journal Geology, described microscopic mineralogical analysis of the Burgess Shale of Canada and the Ediacaran Assemblage of Australia, two of the finest deposits of Cambrian Explosion fossils in the world.  And what the geologists found allowed them to make a guess at where the likes of Opabinia and the rest lived: warm, shallow ocean ecosystems that had water rich in iron.

The iron content allowed the formation of the mineral berthierine, which is not only distinctive in its origins, but has an anti-bacterial effect that halted decomposition and prevented decomposition.  This resulted in the phenomenally well-preserved fossils both sites are known for.

"Berthierine is an interesting mineral because it forms in tropical settings when the sediments contain elevated concentrations of iron," Anderson said.  "This means that Burgess Shale-type fossils are likely confined to rocks which were formed at tropical latitudes and which come from locations or time periods that have enhanced iron.  This observation is exciting because it means for the first time we can more accurately interpret the geographic and temporal distribution of these iconic fossils, crucial if we want to understand their biology and ecology."

The whole thing is tremendously exciting.  To not only have an idea of the appearance of these animals, but to be able to picture them in something like their actual habitat, gives us a glimpse of a world five times older than it was during the heyday of the dinosaurs.  It's breathtaking to think about.

I'll end with a quote from another scientist -- Brian Greene, the physicist whose lucid writing about modern physics in his book The Fabric of the Cosmos inspired an equally brilliant NOVA series.  Greene says: "Science is a way of life.  Science is a perspective.  Science is the process that takes us from confusion to understanding in a manner that's precise, predictive and reliable -- a transformation, for those lucky enough to experience it, that is empowering and emotional."

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The ancestral worm

I live only a few miles from the tallest waterfall in the eastern half of North America, which is not Niagara Falls but Taughannock Falls.

Taughannock (for non-locals, pronounced ta-GAN-uck) Falls is sixty-six meters tall, ten meters higher than Niagara.  It is way narrower than Niagara, and has a far smaller water volume even when it gets rainy around here, but hey, a record is a record.

All that gray rock you see surrounding the narrow thread of the waterfall is Devonian-age shale and limestone, sedimentary rocks deposited about four hundred million years ago when this whole area was at the floor of a shallow sea.  Taughannock Creek has gradually cut its way through the layers of rock, creating a hanging valley at the top of one of the gorges this area is known for -- and exposing literally millions of fossils.

Some of the most common fossils you can find in Taughannock Gorge are brachiopods, shelled animals that look to the untrained eye a bit like a clam.  They're only distantly related to mollusks, however -- the internal structure would make that immediately apparent.  Even the shells show the difference, if you know what to look for.  The easiest way to tell is that bivalve (mollusk) shells are symmetrical across the hinge line, and brachiopods are not.  (Whereas brachiopods are symmetrical across the midline of the shell, and most bivalves aren't.)

Syringothyris texta, an extinct Devonian brachiopod [Image is in the Public Domain]

Although incredibly common as fossils -- I know a couple of places where you can fill your pockets with brachiopod fossils in under fifteen minutes -- they're quite rare as living animals today.  They got hit hard by the Permian-Triassic Extinction (what didn't?) and never really recovered.  There are about thirty thousand species of brachiopods known to the fossil record, of which only a little fewer than four hundred have survived to the day.  Those survivors aren't common anywhere.  They're mainly deep marine species, animals none of us are going to run into on a daily basis.

But that low modern diversity belies what a dominant group they were back before the End Permian Event wiped out an estimated 96% of life on Earth.  Along with trilobites, they were one of the commonest life forms in the planet's oceans before the "Great Dying" of 252 million years ago destroyed them.

What brings all this up is a paper in Current Biology last week describing a fossil found in China that is a good candidate for the common ancestor of brachiopods and the two other groups of lophophorates -- phoronid (horseshoe) worms and bryozoans (moss animals).  Once again, looks are deceiving; these three groups of animals bear little superficial similarity.  The horseshoe worms are sedentary animals that live in U-shaped tubes, and bryozoans are tiny colonial species that look a bit like miniature corals.  But they are alike in internal structure, and all three have a lophophore, a tube-like feeding structure surrounded with tentacles.  And this newly-discovered species, the early Cambrian Wulfengella, looks like it's the right animal in the right place at the right time to be the ancestor of all three groups.

Artist's reconstruction of Wulfengella [Image courtesy of Robert Nicholls, Paleocreations.com]

All of this just goes to show how non-intuitive relationships can be.  Wulfengella doesn't look on first glance anything like any of the three groups it's suppose to be the ancestor to, but its fine structure gives away its kinship.  And it once again highlights how much everything -- the biodiversity, the terrain, the continents themselves -- have changed throughout Earth's history.  We only think things are static because our lives are so short; on the grander scale, the current configurations of the planet will last the blink of an eye.  If you'll indulge me quoting one more time the words of one of my favorite poems, from the eloquent mind of Alfred Lord Tennyson, because I can't think of a better way to close this post:

There rolls the wave where grew the tree.

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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No butts about it

The early Cambrian Period was known for having some weird-looking animals, but even by Cambrian standards, Saccorhytus coronarius was pretty bizarre.

The name is a Greek and Latin composite that means, more or less, "wrinkled bag with a crown," and as disparaging as it sounds I have to admit it's pretty accurate.  The reconstruction of it from various fossils makes it look like a design for a new Pokémon that was rejected on the basis of being too outlandish:

One thing you'll notice about it is that it has no anus.  This, by itself, isn't as odd as it sounds; whole phyla of animals, notably Cnidaria (which includes jellyfish and sea anemones) and Platyhelminthes (flatworms) only have one opening in their digestive tract, meaning once they finish digesting their dinner, they spit the undigested bits out of their mouths.  This lack of a nether orifice has made poor Saccorhytus the butt of many jokes, and in fact I was going to title this post "Assless chaps" but was informed that the more prudish members of my readership might take that the wrong way.

Be that as it may, the spikes combined with its other weird features made it hard to classify.  The first Saccorhytus fossils seemed to have additional holes near the mouth, which initially were thought to be openings for gills but later turned out to be  places where spines had broken off during fossilization.  This has altered our understanding of where it fits on the animal family tree; initially, the supposed gill slits suggested it might be related to deuterostomes (including starfish, sea urchins, sand dollars, and vertebrates).  The fact that this was an artifact of fossilization, coupled with some new research, has placed it instead amongst the Ecdysozoa.  Ecdysozoa is Greek for "animals that get undressed" (speaking of undignified scientific names) because of their ability to shed and regrow their exoskeletons, and includes the familiar phyla Arthropoda, Nematoda, and Tardigrada, as well as less-well-known groups like Priapulida ("penis worms"), which takes "undignified names" to the next level.

Here's the current best-supported arrangement for known animal groups, with the Saccorhytus's branch shown in red:

So that's today's news from the No Ifs, Ands, or Butts department.  (Sorry, I'll stop with the middle-school humor.  Probably.)  Saccorhytus isn't a close relative of ours, but more allied to insects and roundworms.  Still, the lack of a hind end means it's not exactly a comfortable fit in that group either.  Of course, "if you haven’t got an anus," said study lead author Philip Donoghue of the University of Bristol, "you’re not going to be very comfortable anywhere."

Okay, look, that one wasn't my fault.  The scientist himself said it.

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Death, with big nasty pointy teeth

One of the biggest mysteries in paleontology is what caused the Cambrian Explosion.

You probably know that the Cambrian Explosion is when, around 538.8 million years ago, all of the basic body plans of modern animals appeared in a relative flash.  Before that, there were various simple and soft-bodied forms; afterward, there were animals that were clearly arthropods, annelids (segmented worms), mollusks, echinoderms, corals, nematodes, and proto-vertebrates.

In addition, there were also a number of groups of uncertain relationship to better-known lineages, and which went extinct by the end of the Cambrian Period.  One of the weirdest is Opabinia:

[Image licensed under the Creative Commons Nobu Tamura (http://spinops.blogspot.com), Opabinia BW2, CC BY 3.0]

This kind of rapid diversification is usually an indication that something drastic has changed.  One event that sometimes causes this is a large extinction -- leaving behind open niches that the survivors can adapt to fill.  But there appears to have been no major extinction immediately prior to the Cambrian Explosion.

One of the most plausible explanations has its basis in the observation that a lot of the new forms had fossilizable parts -- shells, exoskeletons, teeth, stiff fins and tails adapted for rapid swimming, and so on.  These more durable body parts mostly are either of a defensive or offensive nature.  So perhaps the Cambrian Explosion was triggered when formerly scavenging species realized they didn't have to wait for their friends and neighbors to die to have dinner, and predation was invented.  At that point, there's a hell of a selective pressure for said friends and neighbors to develop structures that protect them from being on the day's menu -- or turn them into predators themselves.

That theory about the origins of the Cambrian Explosion got a significant boost with the recent discovery of a fossil in Charnwood Forest, near Leicester, England, which is the oldest clearly predatory animal known -- and dates to 560 million years ago, so about twenty million years prior to the spike in biodiversity.

It's a relative of modern sea anemones, and was christened Auroralumina attenboroughii, "Attenborough's dawn lantern," after naturalist David Attenborough, who said he was "truly delighted" by the honor.  

[Image licensed under the Creative Commons F. S. Dunn, C. G. Kenchington, L. A. Parry, J. W. Clark, R. S. Kendall & P. R. Wilby, Auroralumina attenboroughii reconstruction, CC BY-SA 4.0]

It's wildly inaccurate to say that "this is the species that caused the Cambrian Explosion," but it certainly is suggestive that predators evolved not that long before the burst in biodiversity began.  "It’s generally held that modern animal groups like jellyfish appeared 540 million years ago, in the Cambrian Explosion, but this predator predates that by twenty million years," said Phil Wilby of the British Geological Survey, who co-authored the study.  "It’s the earliest creature we know of to have a skeleton.  So far we’ve only found one, but it’s massively exciting to know there must be others out there, holding the key to when complex life began on Earth."

It's amazing to think of what the Earth was like back then.  The only life was in the sea, and the vast continents were nothing but bare rock and sand without a single living thing anywhere.  Into that world was born an animal that was one of the first of its kind, a predatory beast with a protective skeleton to make sure that it wouldn't get turned into lunch itself -- launching the evolution of a dizzying array of structures that allowed for fleeing, attacking, and self-protecting, including all of the big, nasty, pointy teeth we see in predatory animals today.

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With fronds like these...

One of the most mystifying, and therefore (to me) one of the most fascinating, paleontological finds is the fauna of the Ediacaran Assemblage.

It's intriguing from a number of perspectives.  First, it gives lie to the picture most people have of the evolution of animals, that it was some kind of linear progression.  It's often seen as a climb up the Great Chain of Being, from something like a jellyfish, to something like a worm, to something like a bug, to fish, amphibians, reptiles, mammals, and finally -- at the top, of course -- is the Pinnacle of Evolution: namely, us.

The truth is (predictably) much more interesting.  During the late Precambrian and early Cambrian Periods, in a relatively short amount of time (geologically and paleontologically speaking) all of the ancestors of the major animal groups appeared, as if there was a sudden and drastic push to diversification.  At that point there were proto-arthropods, proto-vertebrates, proto-mollusks, and proto-damn-near-everything-else.

Even more fascinating is that there were a number of animal groups around during that time that are of uncertain affinity to the others, and who apparently left no descendants.  There's the bizarre Anomalocaris, probably related most closely to early arthropods (its name is Greek for "abnormal shrimp"), with two jointed, spike-lined tentacles and a mouth shaped like a pineapple ring.  Opabinia was equipped with no less than five compound eyes and a proboscis like a vacuum-cleaner hose.  Most famous is the aptly-named Hallucigenia ("it creates hallucinations"), a worm-like critter with giant eyes, tube-like legs, and a double row of formidable spines down the back.

All three of these are probably branches of the huge group Protostomia, which are still today the most numerous animals on Earth.  But there are other fossils from the Ediacaran Assemblage that are even more mysterious, and one of the weirdest ones is the group called rangeomorphs.

They were almost certainly animals, although they were sessile (fixed to the seafloor) via stalks, and had weird frond-like structures of uncertain purpose (but which may have been a mechanism either for oxygen extraction or for filter feeding).  So if you were to look at a living one, your initial impression might well be that it was some odd sort of seaweed, and not an animal at all.

A 550-million-year-old fossil of the rangeomorph Charnia masoni, from the Mistaken Point Formation in Newfoundland [Image licensed under the Creative Commons Smith609 at English Wikipedia, Charnia, CC BY 2.5]

If Anomalocaris, Opabinia, and Hallucinogenia are problematic in terms of their evolutionary affinities, the rangeomorphs are complete ciphers.  They have no obvious connections to any living animal group, and in some ways more resemble fungi, although that too is speculation.  They were apparently quite common during the late Precambrian, so the sea bottom would have been covered with their frilly fronds gently waving in the currents -- but at the moment, exactly what they were is a mystery.

And the mystery just deepened considerably with a discovery that was the subject of a paper last week in Current Biology.  The rangeomorphs had another perplexing and unusual feature -- they were connected by thread-like filaments, some of them up to four meters long, that seem to have hooked populations up into a huge network of interlinked individuals.

The purpose of these filaments is unknown, but it could be that the individuals in a network were all clones, and were functioning as a colonial organism a little like modern corals.  What it immediately put me in mind of was groves of aspens, which look like bunches of individual trees but are all linked underground by a network of rhizomes -- some of the colonies cover many acres, and one in Colorado is said to be over eighty thousand years old.  (This calls into question what we mean by the word "organism;" is each of these trees a separate organism?  Is the whole grove a single organism?  If so, and you dug a trench down the middle and cut the rhizomes, have you just created two organisms?  Like many terms in biology, this word only seems simple until you push on it a little.)

In any case, the rangeomorphs apparently had the world's first social network, but what exactly it was used for we can only speculate at.  They were strange animals to say the very least.  These sorts of discoveries always make me wonder what the Earth looked like back then -- given how infrequent fossilization is, and how unlikely it is for a rock to remain undamaged through all those millions of years, the chances are that for every one species we have a reasonably good picture of, there are hundreds that we know nothing at all about.  The Precambrian water-world of the Ediacaran fauna would have looked a very alien place to our eyes, even though the seeds of all of our modern life-forms -- including ourselves -- were there in those oceans.

Some of those seeds, though, failed to leave behind any progeny, and it seems likely that the rangeomorphs were one of those.  Whatever they were, they certainly show no obvious connections to any modern group, animal or otherwise.  To me this only increases their fascination -- and with it, the hope that further discoveries may shed some light on this and other groups whose origins are lost in the depths of time.

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This week's Skeptophilia book-of-the-week is brand new -- science journalist Lydia Denworth's brilliant and insightful book Friendship: The Evolution, Biology, and Extraordinary Power of Life's Fundamental Bond.

Denworth looks at the evolutionary basis of our ability to form bonds of friendship -- comparing our capacity to that of other social primates, such as a group of monkeys in a sanctuary in Puerto Rico and a tribe of baboons in Kenya.  Our need for social bonds other than those of mating and pair-bonding is deep in our brains and in our genes, and the evidence is compelling that the strongest correlate to depression is social isolation.

Friendship examines social bonding not only from the standpoint of observational psychology, but from the perspective of neuroscience.  We have neurochemical systems in place -- mediated predominantly by oxytocin, dopamine, and endorphin -- that are specifically devoted to strengthening those bonds.

Denworth's book is both scientifically fascinating and also reassuringly optimistic -- stressing to the reader that we're built to be cooperative.  Something that we could all do with a reminder of during these fractious times.

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

Explaining an explosion

One of the most puzzling and fascinating questions in evolutionary biology is what kicked off the Cambrian Explosion.

One striking thing about this event is that it points out how many laypeople have the wrong idea about the progression of evolutionary change.  This view -- perpetuated (unfortunately) by a lot of children's books on prehistoric life -- is that we started out with single-celled organisms, then something like a jellyfish, to something like a worm, to something like a crustacean, and so on and so forth -- until we finally get to humans, who are (of course) the pinnacle and end goal of the whole process.

This is wrong on several counts.

First, evolution is not goal-driven.  It's the law of "whatever works now."  There's no support for the Lamarckian idea of reptiles somehow figuring out that it'd be nice if they could fly, and gradually developing wings.  The evolutionary model shows that when changes occur, they're selected for (or against) by whatever the conditions are at the time.  If those conditions change and what once was an advantage now is a disadvantage, well... sucks to be you.  If the population you belong to has the genetic variation to adapt to the new situation, you might make it as a species.  If not, you'll join the 99% of species on Earth that have vanished entirely.

The second problem that it implies a different length of evolutionary history for each sort of organism -- thus you'll see, sometimes even in otherwise excellent books, sea anemones called "primitive" and octopuses called "advanced."  In fact, sea anemones and octopuses -- and humans -- have precisely the same span of ancestral lineage.  Yes, it's true that in that time, the lineage that led to humans has changed a good bit more; it's also true that we've evolved to be a lot more complex than sea anemones have.  So the words "primitive" and "advanced" have to be used with caution -- because we all trace our ancestry back exactly the same number of years, to a common ancestor some three billion years ago.

Last, and most pertinent to this post, the Cambrian Explosion shows us that the"ladder of creation" view of evolutionary history isn't correct.  The Explosion itself occurred on the order of 541 million years ago, and marks the evolution of most of the major body plans of animals we see today.  So nearly simultaneously, and quite rapidly, the fossil record goes from soft-bodied simple forms to a huge diversity of forms -- early arthropods, proto-vertebrates, mollusks, worms, and echinoderms all appear in a relative flash.

It also generated a few animals we don't see around today -- lineages that left no descendants.  These include Anomalocaris...

[Image licensed under the Creative Commons https://commons.wikimedia.org/wiki/File:Anomalocaris_NT_small.jpg]

... Opabinia...

[Image licensed under the Creative Commons Nobu Tamura (http://spinops.blogspot.com), Opabinia BW2, CC BY 3.0]

... and the aptly-named Hallucigenia.

[Image licensed under the Creative Commons Jose manuel canete, H. sparsa, CC BY-SA 4.0]

The conventional wisdom for years has been that the development of fossilizable parts -- teeth, spikes, armor plates -- came about because of the evolution of carnivory.  Once carnivores are around, there's a significant pressure to evolve structures either for defense or to become a carnivore yourself.

But a paper released last week, from research done at the University of Exeter, has suggested a different cause -- that the roots of the Cambrian Explosion, and thus the biodiversity we see around us today, happened because of plate tectonics.  Plate movements in the early Cambrian resulted in the formation of island arcs, similar to what we see today in Japan and Indonesia, and the resultant volcanic activity dumped so much carbon dioxide into the air that it warmed the planet and boosted phytoplankton growth -- leading to a spike in oxygen and rapid cycling of nutrients that fueled an explosion of animal diversity.

"Many studies have suggested this was linked to a rise in oxygen levels – but without a clear cause for such a rise, or any attempt to quantify it," said Josh Williams, now a Ph.D. candidate at the University of Edinburgh, who was the lead author of the paper.  "What is particularly compelling about this research is that not only does the model predict a rise in oxygen to levels estimated to be necessary to support the large, mobile, predatory animal life of the Cambrian, but the model predictions also show strong agreement with existing geochemical evidence."

Of course, such a complex event is very unlikely to have only a single cause, but the Williams et al. research may have found the initial trigger for the rapid diversification.  It's fascinating to think that a little over half a billion years ago, an episode of volcanism might have been the impetus to generating the animal body plans we still see around us today.  As science has shown us so many times, the key to understanding the present lies in the past.

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Richard Dawkins is a name that often sets people's teeth on edge.  However, the combative evolutionary biologist, whose no-holds-barred approach to young-Earth creationists has given him a well-deserved reputation for being unequivocally devoted to evidence-based science and an almost-as-well-deserved reputation for being hostile to religion in general, has written a number of books that are must-reads for anyone interested in the history of life on Earth -- The Blind Watchmaker, Unweaving the Rainbow, Climbing Mount Improbable, and (most of all) The Ancestor's Tale.

I recently read a series of essays by Dawkins, collectively called A Devil's Chaplain, and it's well worth checking out, whatever you think of the author's forthrightness.  From the title, I expected a bunch of anti-religious screeds, and I was pleased to see that they were more about science and education, and written in Dawkins's signature lucid, readable style.  They're all good, but a few are sheer brilliance -- his piece, "The Joy of Living Dangerously," about the right way to approach teaching, should be required reading in every teacher-education program in the world, and "The Information Challenge" is an eloquent answer to one of the most persistent claims of creationists and intelligent-design advocates -- that there's no way to "generate new information" in a genome, and thus no way organisms can evolve from less complex forms.

It's an engaging read, and I recommend it even if you don't necessarily agree with Dawkins all the time.  He'll challenge your notions of how science works, and best of all -- he'll make you think.

[If you purchase this book using the image/link below, part of the proceeds will go to support Skeptophilia!]

Space mollusks

There's a logical fallacy called the Argument from Personal Incredulity.  The idea here is that you look at something from nature, and find it extraordinary -- beautiful, weird, complex, intricate, or merely bizarre.  Faced with this strange and wonderful thing, you respond, "I can't imagine how this could have come about naturally.  Therefore, it has to be the work of ______."  (Fill in the blank with your favorite deus ex machina, be it gods, aliens, or some other superintelligent power.)

The problem with this, of course, is that saying "I can't imagine how this could happen" only tells you one thing: that you can't imagine how this could happen.  It's not proof of anything else except that whatever-it-is deserves further study.

This approach also gets you into some deep philosophical waters when the extraordinary trait of the example in question is beauty.  You hear people say that gorgeous sunsets or fields of flowers in bloom or whatever are evidence for god's hand in nature, but it conveniently glosses over all the natural things that aren't so nice.  If bunnies and butterflies are god's work, then so are ticks and tapeworms, you know?  Eric Idle pointed this out in his wonderful parody of the hymn "All Things Bright and Beautiful," "All Things Dull and Ugly" -- pointing out that "the Lord God made the lot."

I ran into an example of this -- in a scientific journal, no less -- yesterday, with the paper "Cause of Cambrian Explosion -- Terrestrial or Cosmic?" in the journal Progress in Biophysics and Molecular Biology.  Written by a team of nineteen scientists, it looks at the remarkable expansion of biodiversity that occurred at the beginning of the Cambrian Era, but also considers an evolutionary conundrum -- how the octopus and other cephalopods ended up so much more intelligent than their mollusk relatives.  I'll cut to the chase and tell you their conclusion:

In our view the totality of the multifactorial data and critical analyses assembled by Fred Hoyle, Chandra Wickramasinghe and their many colleagues since the 1960s leads to a very plausible conclusion – life may have been seeded here on Earth by life-bearing comets as soon as conditions on Earth allowed it to flourish (about or just before 4.1 Billion years ago); and living organisms such as space-resistant and space-hardy bacteria, viruses, more complex eukaryotic cells, fertilised ova and seeds have been continuously delivered ever since to Earth so being one important driver of further terrestrial evolution which has resulted in considerable genetic diversity and which has led to the emergence of mankind.

Hoyle and Wickramasinghe are not an auspicious way to start.  They're both associated with the idea of panspermia, that life on Earth was seeded here from outer space, and they don't seem particularly concerned with the fact that there are other, more plausible explanations.  Wickramasinghe especially is associated with a lot of fringe-y claims, such as that the Archaeopteryx type fossil is a forgery and that the virus that caused the 1918-1919 Spanish flu epidemic was extraterrestrial in origin.  He testified for the defense in the 1981 creationism trial in Arkansas, making statements about the "Intelligent Design" model that his colleagues called "absurd" and "ignorant."  (In fact, in papers that mention Wickramasinghe, the phrase most often associated with his name is "his claims have been completely rejected by the scientific community.")

Of course, for some people, being rejected by the establishment is a sign of being brilliant, a maverick, someone whose ideas are ahead of their time.  Their sticking to their guns turns their claims into something of a crusade.  Fewer people, it seems, conclude that the renegade in question is simply wrong.

Which is how we now have a paper in support of Wickramasinghe and Hoyle -- saying, basically, that we have found the extraterrestrials, and they are us.

The part of the paper that addresses viruses is at least looking at a problem for which the standard model has no particularly good explanation.  Viruses are odd beasts, obligate parasites that hijack a host cell and use their cellular machinery to make more copies of themselves.  Some, the retroviruses (HIV being the best-known example) actually insert a bit of their genetic material into the host's cells, rendering infection more or less permanent.  (We have dozens, possibly hundreds, of retroviral remnants in our own DNA, and they have been implicated in a variety of diseases including multiple sclerosis and schizophrenia.)

But then they start talking about octopuses, and leap right off the logical cliff:

[T]he genetic divergence of Octopus from its ancestral coleoid sub-class is very great, akin to the extreme features seen across many genera and species noted in Eldridge-Gould punctuated equilibria patterns (below).  Its large brain and sophisticated nervous system, camera-like eyes, flexible bodies, instantaneous camouflage via the ability to switch colour and shape are just a few of the striking features that appear suddenly on the evolutionary scene.  The transformative genes leading from the consensus ancestral Nautilus (e.g. Nautilus pompilius) to the common Cuttlefish (Sepia officinalis) to Squid (Loligo vulgaris) to the common Octopus (Octopus vulgaris) are not easily to be found in any pre-existing life form – it is plausible then to suggest they seem to be borrowed from a far distant “future” in terms of terrestrial evolution, or more realistically from the cosmos at large.  Such an extraterrestrial origin as an explanation of emergence of course runs counter to the prevailing dominant paradigm.

The last bit, at least, is undeniable.  They go on to add:

One plausible explanation, in our view, is that the new genes [i.e., differences between the octopus genome and that of their nearest relatives] are likely new extraterrestrial imports to Earth - most plausibly as an already coherent group of functioning genes within (say) cryopreserved and matrix protected fertilized Octopus eggs. 

Thus the possibility that cryopreserved Squid and/or Octopus eggs, arrived in icy bolides several hundred million years ago should not be discounted as that would be a parsimonious cosmic explanation for the Octopus' sudden emergence on Earth ca. 270 million years ago.

The problem here is that their entire argument rests on two things: (1) the lack of a good fossil record of the octopus; and (2) their amazing intelligence.  So we're adding the Argument from Ignorance ("I don't know the explanation, so it must be ____") to the Argument from Personal Incredulity ("It's pretty cool, so it must be ____") to the paucity of the fossil record (not only for octopuses, but for most life forms) and concluding that the octopus came to Earth via frozen eggs from outer space.

[Image is in the Public Domain]

There's also a serious scientific stumbling block about all this, and it's one the authors don't address.  It's the same problem faced by claims of human/alien hybridization; if life did evolve on other worlds, there is no reason in the world that it would necessarily encode its genetic information the same way we do.  Something like DNA or RNA is probably fairly likely; the nucleotides (building blocks) of these molecules are relatively easy to synthesize, and RNA has the unusual characteristic of being autocatalytic (it can catalyze its own chemical reactions).  But the DNA code chart -- the master recipe book by which our genetic material is decoded, and directs all of our cellular processes -- appears to be entirely arbitrary.

And yet... it is shared by all life forms on Earth.  Including the octopus.  Good evidence that we all came from a common ancestor -- and a tough thing to overcome if you think that some terrestrial life forms came from elsewhere in the galaxy.

So if we have scant evidence for something, we don't engage in wild speculation -- we look for more evidence.  You can't base a valid conclusion either on ignorance or awe.  And to cherry-pick a few odd examples of creatures the Darwinian model hasn't fully explained, and use them to support your claim that life's evolutionary drivers came from outer space, is nothing more than fancily-worded confirmation bias.

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This week's recommended book is an obscure little tome that I first ran into in college.  It's about a scientific hoax -- some chemists who claimed to have discovered what they called "polywater," a polymerized form of water that was highly viscous and stayed liquid from -70 F to 500 F or above.  The book is a fascinating, and often funny, account of an incident that combines confirmation bias with wishful thinking with willful misrepresentation of the evidence.  Anyone who's interested in the history of science or simply in how easy it is to fool the overeager -- you should put Polywater by Felix Franks on your reading list.