Wipeout

252 million years ago, the Earth was hit by a confluence of Very Unfortunate Events.

First, most of the large continental land masses locked up into a single supercontinent, Pangaea.  This had multiple effects, including alterations of oceanic currents, massive desertification, and the collapse of the convection cells powering seafloor spreading at mid-ocean ridges.  The latter caused a drastic lowering of sea level and exposure of continental shelves, reducing habitat for marine species that live in shallow water (which is most of them).

Second, the tinder box that had formed in the Carboniferous Period -- enormous deposits of coal, oil, and limestone produced when the Earth was basically one giant greenhouse -- found its lit match when the Siberian Traps erupted.  This is one of the largest volcanic events known, and produced an almost unimaginable four million cubic kilometers of basaltic lava.  This ripped through all that coal and carbonate rock, releasing catastrophic amounts of carbon dioxide and sulfur dioxide into the atmosphere.  The portion of the excess absorbed into the ocean caused acidification, killing any marine animal with carbonate shells or skeletons.  The resulting temperature rise caused worldwide oceanic anoxia.  It very likely also triggered the unraveling of unstable methane clathrate deposits on the seafloor, releasing gaseous methane and further boosting the temperature.

If that weren't enough, right around this time the Araguainha Impactor hit what is now Brazil.  The spot where it struck was at the time mostly composed of another gift from the Carboniferous -- oil shale.  This was flash-incinerated, releasing yet more carbon dioxide.

The result: the extinction of between 80% and 95% of the species on Earth, depending on how you count them and who you ask.  

What there's no doubt of, though, is that it was devastating.  It's the closest the Earth has come to undergoing a complete wipeout.  Entire taxa went extinct, including eurypterids (sea scorpions), trilobites, blastoids, tabulate and rugose corals, and acanthoid fish; 99% of radiolarian species vanished, as well as 98% of gastropods and 97% of ammonites and foraminiferans.  The entire food web collapsed.

Afterward, the Earth was an overheated, sulfur-smelling, hypoxic, largely lifeless wasteland.

And yet, somehow, it recovered.  How exactly the Earth's living things made it through the largest bottleneck ever is the subject of a paper last week in the Geological Society of America Bulletin, authored by a team from University College Cork, the University of Connecticut, and the Natural History Museum of Vienna.  And what it found was that the bounce-back didn't happen all at once.  It was far from a linear progression toward rebuilding the biosphere -- there were further shifts and setbacks over several million years as life "found a way."

The team focused mainly on the plants, given that they're the base of the food web.  Some of the first recolonizers were conifers, but they suffered a reversal not even a million years after the main pulse of extinctions with the Smithian-Spathian Boundary Event, a further spike in global temperature that ultimately saw sea surface temperatures of 40 C (104 F), but which was then followed by an unexplained and equally rapid drop.  The wild pendulum swings in temperature caused the collapse of the resurgent coniferous forests; ultimately they were replaced by seed ferns and club mosses (the latter were larger than the ones we have today, but not as big as the enormous Lepidodendrons that were around during the Carboniferous).  

An early Triassic seed fern, Lepidopteris [Image licensed under the Creative Commons Vivi Vajd, Stephen McLoughlin, Sam M. Slater, Ola Gustafsson, Allan G. Rasmusson, Lepidopteris life restoration, CC BY 4.0]

Eventually the climate stabilized, but any way you spin it, the Early Triassic Period was a horrible time to be alive.  It was largely hot and dry, but then -- with startling rapidity -- terrestrial biomes were swamped during the weird Carnian Pluvial Episode, a two-million-year-long thunderstorm which I wrote about not long ago.  Then, at the end of the Triassic, there was yet another massive extinction, this one probably caused by the volcanism from the Central Atlantic Magmatic Province (which would ultimately open the Atlantic Ocean).  Things had largely settled down by the beginning of the Jurassic Period, at which point we were heading into a period of lush forests and (mostly) stable climate -- the long, glorious Age of Dinosaurs.

But as you know, even their salad days weren't destined to last forever.

It always strikes me, when I read papers like this one -- the colossal hubris and ignorance of people who think we can mess around with Earth's ecosystems with complete impunity.  They often shrug off any Cassandras with breezy lines like, "The Earth's climate has had swings in the past, and has always recovered."  And in one sense, sure, that's true.  Faced even with a catastrophic extinction like the Permian-Triassic, enough species made it through the bottleneck -- and the whipsawing that happened afterward, as the climate gradually restabilized -- to repopulate the Earth.

But keep in mind that a great many species didn't make it.  Most of them, in fact.  Then, at the end of the Cretaceous, the non-avian dinosaurs -- that had been the dominant group worldwide for two hundred times longer than humans have existed -- were completely eliminated.  Okay, life recovered once again, but even for the survivors, living through the event itself was no fun.

Oh, and allow me to put this whole grim story into perspective by mentioning the second paper that came out this week; a huge study out of James Cook University and the University of Adelaide showing unequivocally that tropical forests are dying off because of human-induced climate change -- that they're not adapting fast enough to cope with how quickly we're altering the climate.

We are the first species that has sufficient brainpower to understand how our actions affect the biosphere, and (perhaps) enough power to work toward mitigating them.  And instead, we're largely doing nothing, selling out the future in exchange for short-term expediency, a use-it-once-then-throw-it-away lifestyle, and enriching the coffers of corporate billionaires.  The current so-called administration's mottos with regards to the environment are "Deregulate everything," "Cut down more trees," and "Drill, baby, drill."

They, and all of us, should remember: sure, it's likely that whatever we do, in a million years there still will be plenty of life on Earth.  No matter the mistakes we make, the biosphere will survive.

But there is no guarantee that the survivors will include us.

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The return of Lieutenant Kijé

Ever heard the story of Lieutenant Kijé?

He's the subject of a 1927 comic film made in the Soviet Union.  Set in the time of Tsar Paul I, it's the tale of a visit by the Tsar to a military outpost.  One night, the Tsar is awakened by a noise -- it's the sound of one of the officers getting a little too frisky with a young woman in an adjoining room -- and when the regiment commander is confronted about the outrage the next morning, he blames it on a (nonexistent) "Lieutenant Kijé."  ("Kijé" is a slang word meaning approximately the same thing as "whatchamacallit.")  The indignant Tsar demands to meet with this errant officer -- so the panicked commander says he can't, the matter is already settled, Kijé is in the brig and will be shipped off to Siberia.

Soon after, however, the real culprit's identity comes out, and the Tsar demands that the commander not only release and apologize to the wronged Lieutenant Kijé, but promote him to the rank of colonel.  Repeated requests by the Tsar to meet Kijé result in more and more elaborate stories made up about him explaining why this can't happen -- first that Kijé was on leave because he was getting married to the lovely Princess Gagarina, then because he's away at battle (which, of course, results in a brilliant triumph).  Finally, though, the whole house of cards can't be sustained any longer.  The Tsar demands to meet this valiant pinnacle of an officer so he can personally promote him to general.

The commander and the others who are in on the lie have no choice.  They invent one final story -- that the brave Colonel Kijé has tragically died a heroic death in battle.  Sad as it is to have to tell His Majesty the Tsar, there will never be an opportunity to meet this exemplary soldier in person.

The story only became known outside of Russia because of the absolutely delightful score for the film written by the brilliant Sergei Prokofiev -- the Lieutenant Kijé Suite is still a staple of the classical orchestral repertoire today.

I started thinking about the story Lieutenant Kijé this morning because of our own Tsar, Donald Trump.

If you watched the State of the Union address -- or, if (like me) you read excerpts because you can only listen to Trump's voice for about fifteen seconds without wanting to remove your ears, with a cheese grater if it's the only thing handy -- you probably know that he babbled on (and on and on) about government waste, citing eight million dollars that had been spent to "create transgender mice."  I probably don't need to tell you that this was an idiotic error.  The mice weren't transgender, they were transgenic.  Transgenic organisms are ones that have been genetically modified, in this case to engineer their immune systems to respond more like a human's would.  Transgenic organisms are a staple of medical research, especially into cancer, asthma, and autoimmune diseases.

Transgender mice, on the other hand, do not exist.

Naturally, anyone with an IQ higher than their hat size laughed directly into Trump's face for making such a moronic pronouncement (and in the State of the Union address, no less, in front of literally millions of watchers).  So what do you think his advisors did in response?  Issue some kind of "the President misspoke, and we'd like to correct it" statement?

Ha.  Of course not.  They started frantically going through every scrap of research involving mice they could find to see if they could come up with one that had anything to do with gender.  There's no way they could tell Tsar Donald he'd fucked up.

All they found was an obscure 2019 study that had to do with the role of stress in sexual development in mice, and said, basically, "Here it is!  This is what he was talking about!"  Never mind that (1) it was definitely not what he was talking about, (2) the 2019 study itself was published during Trump's first term, so hardly can be used as an example of wasteful spending today, (3) it still has nothing to do with mice (or anyone else) being transgender, and (4) Trump is so catastrophically stupid there's no way he's even capable of reading and understanding a scientific abstract, much less an academic paper in its entirety.

Then, when people pointed out the above, they doubled down again.  (Tripled down?)  They put out an official statement that yes, Biden did so waste money on transgender mice.  You ready for the studies they cited?

• a study to find out if hormone therapy affects the immune response in patients with HIV
• a study looking at how steroid hormone administration affects fertility
• a study of the effects of testosterone on breast cancer susceptibility
• a study of how hormone administration affects the microbiome
• a study of how reproductive hormones affect neurological development in embryos
• a study of how reproductive hormones affect asthma

All of that justifiable medical research.  None of it having anything to do with "making mice transgender."  The only connection with being transgender is that some of the hormones under study are the ones used in gender transition in humans.

So it's another reprehensible attack using the current furor over LGBTQ+ people to whip up the base, and has only a glancing connection to the truth.  But Trump's cronies had to keep defending it, because how else were they to keep up the appearance that the Tsar knows what he's talking about, and appease the "Trump Was Right About Everything!" crowd?

It's the same colossally ignorant approach that "DOGE" has used -- purging projects involving keywords (or syllables) like "diversity" and "trans" and accidentally trashing projects studying things like biodiversity and transnational terrorism.  There have now been at least three instances of mass firings that have led to the people in charge going "Oopsie" and trying to rehire the fired workers with only partial success -- at the FAA, the nuclear weapons oversight team at the Department of Energy, and the Center for Disease Control.

The bottom line is that the people now running the government aren't just greedy and amoral, they're fundamentally, deeply, and irrevocably stupid.  And -- like the Tsar in Lieutenant Kijé -- they have surrounded themselves by sycophantic toadies who are afraid to stand up and say, "Wait a moment.  You can't make that claim, it's false."  Or, in the case of "DOGE," that maybe hiring a bunch of hackers and then running around the place with a chainsaw is not the way to approach pulling back the reins on wasteful spending.

But I fear that the farce will continue.  When you're dealing with a man who has a bloated ego, has never been given a single meaningful consequence for wrongdoing in his entire life, has a whipcrack temper, and is in one of the most powerful elected positions in the world, we're going to see more of this kind of behavior.  All we can do is to continue to use our voices as strongly as we are able, and call out this sort of nonsense whenever we see it or hear it.

And keep in mind that even the tsars, as powerful as they were, did not last forever.

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Deep impact

It's remarkably hard to find evidence of impact craters on the Earth.

If you're thinking, "What's the difficulty?  Just look for a big hole in the ground," you're probably thinking of one of two things -- either craters on the Moon, or Barringer Crater near Winslow, Arizona.  The craters on the Moon stick around pretty much indefinitely because the airless, waterless surface experiences virtually no erosion; as far as Barringer, the impact that caused it only happened around fifty thousand years ago, which is the blink of an eye, geologically speaking.  (Plus, it's in the high desert, with little vegetation to hide underneath.)

With older impact craters, the forces of erosion eat away at the telltale signs -- the raised, oval or circular ridges, especially.  The oldest craters have been destroyed by subsequent tectonic shifts and faults, and (for ones in oceanic plates) because the damaged strata themselves were subducted and melted.

One massive impact crater that was only detected in 1983 -- despite the fact that tens of thousands of people live more or less right on top of it -- is the one left by the Chesapeake Bay Impact Event, which occurred during the Eocene Epoch, on the order of 35.5 million years ago.  At that point, the impact site, on the southern tip of the Delmarva Peninsula, was coastal tropical rainforest; the global temperature was still dropping following the massive Paleocene-Eocene Thermal Maximum, but was still a good two degrees Celsius warmer than today.  The mass of the impactor isn't known for certain -- it was completely vaporized -- but it's estimated to have been about three kilometers across and traveling at eighteen kilometers per second, and punched a hole eight kilometers deep into the crystalline basement rock, blasting the sediments on top to smithereens and creating a crater over eighty kilometers across.  Because at least part of the impact was in the shallow ocean, it also created a massive tsunami that travelled inland as far as the foothills of the Blue Ridge Mountains.

Since the impact, it refilled -- first with unconsolidated, unsorted sediments, essentially broken up pieces of the rock that was blown out from the collision, then with eroded material as the whole place gradually settled down.  Part of it was refilled with seawater.  The only way it was discovered was the presence of an anomalous "fault" that turned out to be the edge of the crater wall, followed by the analysis of some rock cores that showed a huge, thick layer of jumbled junk that geologists figured out was the debris formed as the crater walls slumped inward.  It also explained the North American Tektite Field, an enormous splatter field of what amounts to cooled droplets of melted rock.

But visiting the area today, you don't see much that would tell you that only thirty-five million years ago, the place got slammed by an enormous chunk of rock from outer space.

[Image is in the Public Domain courtesy of the United States Geological Survey]

Even the much larger Chicxulub Impact Crater, near the Yucatán Peninsula, took a lot of work to identify.  It's just shy of twice as old as the Chesapeake Bay site (about 66 million years), and is almost entirely underwater and filled with oceanic sediments.  Today, the impact site that ended the 180-million-year hegemony of the dinosaurs is only visible to sensitive gravitometers and magnetometers.

Which makes the discovery of an impact crater 3.47 billion years old, in East Pilbarra, Western Australia, even more astonishing.

A paper in Nature Communications this week, authored by Christopher Kirkland of Curtin University et al., shows convincing evidence of an impact crater over a hundred kilometers wide near the northwestern coast of Australia.  The center of the crater shows regions of shocked crystalline rock, along with layers of breccia (the same sort of jumble of debris found at the Chesapeake Bay site).  Further stratigraphic work has confirmed that this was, indeed, the site of a "massive hypervelocity impact."  This makes it the only Archaean-age crater known to have survived.

The authors write:

Despite the high modeled frequency of bolide impacts in the early Archaean, the rarity of verified impact craters of Archaean age suggests that: (a) the impact flux was much less than predicted by lunar data; (b) the evidence has been eradicated, or (c) that we have failed to recognise them.  On a young Earth covered in primitive (mafic–ultramafic) crust, identifying shatter cones or impact breccias may represent the best chance of finding other large Archaean impact structures.  However, these highly fractured rocks will be the first to undergo (presumably intense) weathering and erosion.  Notwithstanding their fragility, we believe many more Archaean craters await discovery.

Myself, I think it's astonishing that they've found even one.  For any traces to have survived for nearly three and a half billion years is staggering.  At that point, life was only getting started; the first known microbes appeared 3.7 billion years ago, and when the impact occurred, it would still be another half a billion years before the first certain multicellular life.  So unlike the Chesapeake Bay and Chicxulub Impacts, which were (respectively) regionally and globally devastating to life, the East Pilbarra collision probably didn't make much of... um... an impact.

But it definitely stirred things up, created an enormous crater and rain of debris, and would have been a dramatic thing to witness.  From a safe distance.  The fact that even today, 3.47 billion years later, geologists can detect the hole it left behind, indicates that it was one hell of a punch.

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Spin cycle

Well, The Daily Mail Fail is at it again, this time with a claim that the CIA has declassified a book predicting the end of the world (which is going to happen soon, of course).  Illustrating the fact that there is no conspiracy theory so blatantly idiotic that there won't be people passionately espousing it, the whole thing has the End Times crowd running around making excited little squeaking noises, while the rest of us are wearing expressions like this:

The book is called The Adam and Eve Story, which should put you on notice immediately that we're not talking about hard science, here.  It's by a guy named Chan Thomas, a "former U.S. Air Force employee, UFO researcher, and self-acclaimed psychic," for whom, we're told, "there are no official records of [his] working directly for the CIA."

So we're definitely off to a flying start.

I guess there's no doubt that the guy's book, which was written in 1966, was considered classified until 2013, and only appeared on the CIA's database of declassified documents about a month ago -- and then, only 55 pages out of the two hundred or so in the original manuscript.  Why it was classified in the first place is uncertain, although it may be nothing more than the fact that anyone who worked on any sort of sensitive-to-security projects -- which Thomas apparently did -- automatically has anything they write classified until it can be reviewed and shown not to give away anything that needs to stay secret.

My surmise is the fact that it languished after that because no one at the CIA took it seriously enough to bother reviewing.

Anyhow, Thomas's claim is that there have been cataclysms on the order of every six thousand years, and we're currently overdue.  What happens during these catastrophes illustrates the fact that Thomas shoulda stuck with UFO research, or at least paid better attention during ninth grade Earth Science class, because the first thing that jumps out at me is that he does not understand the difference between the Earth's rotational axis and its magnetic poles.  This leads him to conclude that when the magnetic poles flip -- something that happens around every three hundred thousand years, not six thousand, so he's off by a factor of fifty, but who's counting -- it somehow affects the rotational axis, throwing continents and oceans around like a washing machine on spin cycle.  

The results are hella scary.  Thomas writes:

In a fraction of a day all vestiges of civilization are gone, and the great cities — Los Angeles, San Francisco, Chicago, Dallas, New York — are nothing but legends.  Barely a stone is left where millions walked just a few hours before...  Winds with the force of a thousand armies will shred everything in sight with a supersonic bombardment, as a Pacific tsunami drowns Los Angeles and San Francisco as if they were but grains of sand...  Calamity will overtake the entire North American continent within three hours, as an earthquake simultaneously creates massive cracks in the ground that allow magma to rise to the surface.

So I think we all can agree that this would be bad.  By the time it's all over -- in seven days, he says -- everything will be rearranged, with Antarctica at the equator (melting its huge ice caps), and the Bay of Bengal at what is now the North Pole.

By now you may be wondering what historical cataclysms "every six thousand years" he's basing this on.  I know I was.  You ready?

The Flood of Noah, and six thousand years before that, something about Adam and Eve.  (You might have guessed the latter based on the book's title; I have to admit by that point I'd already forgotten it, so this got an all-new eyeroll from me.)

Scholars of the Bible might be objecting by now that the Book of Genesis doesn't describe any kind of worldwide catastrophe centering around Adam and Eve, just some malarkey about a serpent and an apple and whatnot, and their being the ancestors of all humanity despite supposedly being the first people and having only sons.  But Thomas seems sufficiently detached from reality that this is only a minor quibble compared to some of the other stuff he says.

Despite the fact that the claim is (in a word) ridiculous, I've already seen three videos on TikTok that seem to treat the whole thing as deadly serious, with the fact that three-quarters of the original manuscript is still classified being used as evidence that the CIA is "hiding something" and "they're trying to prevent mass panic."

Trust me, the only people out there panicking over this are ones who see messages from God on their grilled cheese sandwiches.  And it hardly bears pointing out that you can't use pages you've never seen as proof of anything, given that by default we don't know what's in them.

Sometimes absence of evidence really is evidence of absence.

In any case, I wouldn't lose any sleep over this.  But I will appeal to the conspiracy theorists: can you please try and give me better material to work with?  Because this one was kind of bottom-of-the-barrel.  Time to step up your game, folks.  It's positively making me pine for the good old days of HAARP and Nibiru and the Annunaki and "Birds Aren't Real."

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Watch your tone!

You probably know that there are many languages -- the most commonly-cited are Mandarin and Thai -- that are tonal.  The pitch, and pitch change across a syllable, alter its meaning.  For example, in Mandarin, the syllable "ma" spoken with a high steady tone means "mother;" with a falling then rising tone, it means "horse."

If your mother is anything like mine was, confusing these is not a mistake you'd make twice.

A pitch vs. time graph of the five tones in Thai [Image licensed under the Creative Commons Thtonesen.jpg: Lemmy Laffer derivative from Bjankuloski06en, Thai tones, CC BY-SA 3.0]

English is not tonal, but there's no doubt that pitch and stress change can communicate meaning.  The difference is that pitch alterations in English don't change the denotative (explicit) meaning, but can drastically change the connotative (implied) meaning.  Consider the following sentence:

He told you he gave the package to her?

Spoken with a neutral tone, it's simply an inquiry about a person's words and actions.  Now, one at a time, change which word is stressed:

• He told you he gave the package to her?  (Implies the speaker was expecting someone else to do it.)
• He told you he gave the package to her? (Implies surprise that you were told about the action.)
• He told you he gave the package to her? (Implies surprise that you were the one told about it)
• He told you he gave the package to her? (Implies the speaker expected the package should have been paid for)
• He told you he gave the package to her? (Implies that some different item was expected to be given)
• He told you he gave the package to her? (Implies surprise at the recipient of the package)

Differences in word choice can also create sentences with identical denotative meanings and drastically different connotative meanings.  Consider "Have a nice day" vs. "I hope you manage to enjoy your next twenty-four hours," and "Forgive me, Father, for I have sinned" vs. "I'm sorry, Daddy, I've been bad."

You get the idea.

All of this is why mastery of a language you weren't born to is a long, fraught affair.

The topic comes up because of some new research out of Northwestern University that identified the part of the brain responsible for recognizing and abstracting meaning from pitch and inflection -- what linguists call the prosody of a language.  A paper this week in Nature Communications showed that Heschl's gyrus, a small structure in the superior temporal lobe, actively analyzes spoken language for subtleties of rhythm and tone and converts those perceived differences into meaning.

"Our study challenges the long-standing assumptions how and where the brain picks up on the natural melody in speech -- those subtle pitch changes that help convey meaning and intent," said G. Nike Gnanataja, who was co-first author of the study.  "Even though these pitch patterns vary each time we speak, our brains create stable representations to understand them."

"The results redefine our understanding of the architecture of speech perception," added Bharath Chandrasekaran, the other co-first author.  "We've spent a few decades researching the nuances of how speech is abstracted in the brain, but this is the first study to investigate how subtle variations in pitch that also communicate meaning are processed in the brain."

It's fascinating that we have a brain area dedicated to discerning alterations in the speech we hear, and curious that similar research on other primates shows that while they have a Heschl's gyrus, it doesn't respond to changes in prosody.  (What exact role it does have in other primates is still a subject of study.)  This makes me wonder if it's yet another example of preaptation -- where a structure, enzyme system, or gene evolves in one context, then gets co-opted for something else.  If so, our ancestors' capacity for using their Heschl's gyri to pick up on subtleties of speech drastically enriched their abilities to encode meaning in language.

But I should wrap this up, because I need to go do my Japanese language lessons for the day.  Japanese isn't tonal, but word choice strongly depends on the relative status of the speaker and the listener, so which words you use is critical if you don't want to be looked upon as either boorish on the one hand, or putting on airs on the other.

I wonder how the brain figures all that out?

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Birds, bees, etc.

Yesterday I was thinking about sex.

Not like that.  My intention is to keep this blog PG-13.  I meant sexual reproduction in general, and the topic comes up because I just finished reading Riley Black's lovely new book When the Earth Was Green: Plants, Animals, and Evolution's Greatest Romance, which looks at paleontology through the lens of botany.  It's a brilliant read, the writing is evocative and often lyrical, and it needs to be added to your TBR list if you've even the slightest bit more than a passing interest in the past.

One of the topics she looks at in some detail is how sexual reproduction in plants -- better known as pollination -- led to an inseparable relationship between flowering plants and their pollinators.  A famous example is Darwin's orchid (Angraecum sesquipedale), a Madagascar species with night-scented white flowers whose nectaries are at the base of an impossibly long tube:

[Image licensed under the Creative Commons Bernard DUPONT from France, Darwin's Orchid (Angraecum sesquipedale) (8562029223), CC BY-SA 2.0]

Its discovery prompted Charles Darwin to predict that there must be a moth on the island whose mouthparts fit the flower, and which was responsible for pollinating it.  Sure enough, in a few years, biologists discovered the Madagascar hawk moth (Xanthopan morganii):

[Image licensed under the Creative Commons Nesnad, Xanthopan morganii praedicta Sep 16 2021 03-58PM, CC BY 4.0]

The problem is, such dramatic specialization is risky.  If something happens to either member of the partnership, the other is out of luck.  In fact, sexual reproduction in general is a gamble, but its advantages outweigh the risk, and I'm not just talking about the fact that it's kind of fun.

Asexually-reproducing organisms, like many bacteria and protists, some plants and fungi, and a handful of animals, have the advantages that it's fast, and only requires one parent.  There's a major downside, however; a phenomenon called Muller's ratchet.  Muller's ratchet has to do with the fact that the copying of DNA, and the passing of those copies on to offspring, is not mistake-proof.  Errors -- called mutations -- do happen.  Fortunately, they're infrequent, and we even have enzymatic systems that do what amounts to proofreading and error-correction to take care of most of them.  A (very) few mutations actually lead to a code that works better than the original did, but the majority of the ones that slip by the safeguards cause the genetic message to malfunction.

It's called a "ratchet" because, like the handy tool, it only turns one way -- in this case, from order to chaos.  Consider a sentence in English -- space and punctuation removed:

TOBEORNOTTOBETHATISTHEQUESTION

Now, let's say there's a random mutation on the letter in the fourth position, which converts it to:

TOBGORNOTTOBETHATISTHEQUESTION

The message is still pretty much readable, although the second word is now spelled wrong.  But most of us would have been able to figure out what it was supposed to say.

Now, suppose a second mutation strikes.  There is a chance that it would affect the fourth position again, and purely by accident convert the erroneous g back to an e, but that likelihood is vanishingly small.  This is called a back mutation, and is more likely in DNA -- which, of course, is what this is an analogy to -- because there are only four letters (A, T, C, and G) in DNA's "alphabet," as compared to the 26 English letters.  But it's still unlikely, even so.  You can see that at each "generation," the mutations build up, every new one further corrupting the message, until you end up with a string of garbled letters from which not even a cryptographer could puzzle out what the original sentence had been.

Sexual reproduction is a step toward remedying Muller's ratchet.  Having two copies of each gene (a condition known as diploidy) makes it more likely that at least one of them still works.  Many genetic diseases -- especially the ones inherited as recessives -- are losses of function, where copying errors have caused that stretch of the DNA to malfunction.  But if you inherited a good copy from your other parent, then lucky you, you're healthy (although you can still pass your "hidden" faulty copy on to your children).

This, incidentally, is why inbreeding -- both parents coming from the same genetic stock -- is a bad idea.  It doesn't (in humans) cause problems in brain development, which a lot of people used to think.  But what it does mean is that if both parents have a recent common ancestor, the faulty genes one of them carries are very likely the same ones the other does, and the offspring has a higher chance of inheriting both damaged copies and thus showing the effects of the loss of function.  It's this mechanism that explains why a lot of human recessive genetic disorders are characteristic of particular ethnic groups, such as cystic fibrosis in northern Europeans, Tay-Sachs disease in Ashkenazic Jews, and malignant hyperthermia in French Canadians.  It only happens when both parents are from the same heritage -- which is why "miscegenation laws," preventing intermarriage between people of different races or ethnic backgrounds, are exactly backwards.  Mixed-race children are actually less likely to suffer from recessive genetic disorders -- the mom and dad each had their own "genetic load" of faulty genes, but there was no overlap between the two sets of errors.  Result: healthy kid.

The difficulty, of course, is that despite its genetic advantages, sexual reproduction requires a genetic contribution from two parents.  This is tough enough with mobile species, but with organisms that are stuck in place -- like plants -- it's a real problem.  Thus the hijacking of animals as carriers for pollen, and the evolution of a host of mechanisms for preventing self-pollination (which cancels out the advantage of higher variation, given that once again, both sets of genes come from the same parent).

What's most curious about sexual reproduction is that we don't know how it started.  Even some very simple organisms have genetic exchange mechanisms, such as conjugation in bacteria, which help them not to get clobbered by Muller's ratchet, and something like that is probably how it got going in the first place.  We know sexual reproduction is evolutionarily very old, given that it's shared by the majority of life on Earth, but how the process of splitting up and recombining genetic material every generation first started is still a mystery.

Anyhow, that's our consideration of birds, bees, and others for the day.  I'll end by saying again that you should buy Riley Black's book, because it's awesome, and gives you a vivid picture of life at various times on Earth, not from the usual Charismatic Megafauna viewpoint, but from the perspective of our green friends and neighbors.  It's refreshing to consider how life is experienced from an entirely different angle every once in a while.

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Lost horizon

While our knowledge of the origin of the universe has grown tremendously in the past hundred years, there are still plenty of cosmological mysteries left to solve.

One of the most vexing is called the horizon problem.

It's one of those situations where at first, it seems like "where's the problem?"  Then you look into it a little more, and kind of go, "... oh."  The whole thing has to do with how fast a change can percolate through a system.  Amongst the (many) outcomes of the General Theory of Relativity, we are reasonably certain that the upper bound at which disturbances of any kind can propagate is the speed of light.

So if a change of some sort happens in region A, but it is so far away from region B that there hasn't been enough time for light to travel between the two, it is fundamentally impossible for that change to have any effect at all in region B.  Such regions are said to be causally disconnected.

So far, so good.  The thing is, though, there are plenty of sets of causally disconnected regions in the universe.  If at midnight in the middle of winter you were to aim a very powerful telescope straight up into the sky, the farthest objects you could see are on the order of ten billion light years away.  Do the same six months later, in midsummer, and you'd be looking at objects ten billion light years away in the other direction.  The distance between the two is therefore on the order of twenty billion light years (and this is ignoring the expansion of the universe, which makes the problem even worse).  Since the universe is only something like 13.8 billion years old, there hasn't been enough time for light to travel between the objects you saw in winter and those you saw in summer.

Therefore, they can't affect each other in any way.  Furthermore, they've always been causally disconnected, at least as far back as we have good information.  By our current models, they were already too far apart to communicate three hundred thousand years after the Big Bang, the point at which decoupling occurred and the 2.7 K cosmic microwave background radiation formed. 

Herein lies the problem.  The cosmic microwave background (CMB for short) is very nearly isotropic -- it's the same no matter which direction you look.  There are minor differences in the temperature, thought to be due to quantum fluctuations at the moment of decoupling, but those average out to something very close to uniformity.  It seems like some process homogenized it, a bit like stirring the cream into a cup of coffee.  But how could that happen, if opposite sides of the universe were already causally disconnected from each other at the point when it formed?

A map of the CMB from the Wilkinson Microwave Anisotrophy Probe [Image is in the Public Domain courtesy of NASA]

It's worse still, however, which I just found out about when I watched a video by the awesome physicist and science educator Sabine Hossenfelder a couple of days ago.  Because a 2003 paper found that the CMB isn't isotropic after all.

I'm not talking about the CMB dipole anisotropy -- the fact that one region of the sky has CMB a little warmer than average, and the opposite side of the sky a little cooler than average.  That much we understand pretty well.  The Milky Way Galaxy is itself moving through space, and that creates a blue shift on one side of the sky and a red shift on the other, accounting for the measurably warmer and cooler regions, respectively.

What Hossenfelder tells us about is that there's an anisotropy in the sizes of the warm and cool patches.  It's called the hemispherical power spectrum asymmetry, and simply put, if you sort out the sizes of the patches at different temperatures, you find that one side of the sky is "grainier" than the other.  Like I said, we've known about this since 2003, but there was nothing in any of the models that could account for this difference, so cosmologists kind of ignored the issue in the hopes that better data would make the problem go away.

It didn't.  A recent paper using newly-collected data from the Planck mission found that the hemispherical power spectrum asymmetry is real.

And we haven't the first idea what could have caused it.

In a way, of course, this is tremendously exciting.  A great many scientific discoveries have started with someone looking at something, frowning, and saying, "Okay, hang on a moment."  Here we have something we already didn't understand (CMB isotropy and the horizon problem) gaining an added layer of weirdness (it's not completely isotropic after all, but is anisotropic in a really strange way).  What this shows us is that our current models of the origins of the universe are still incomplete.

Looks like it's a good time to go into cosmology.  In what other field is there a universe-sized problem waiting to be solved?

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