Dangerous reflection

Last week I ran across an article in the journal Science about our capacity for creating "mirror life," and the risks thereof.  I considered addressing the topic here, but after some thought concluded that the human race has more pressing things to worry about at the moment, such as climate change, global pandemics, terrorism, environmental collapse, and Donald Trump opening the Seventh Seal of the Apocalypse because he thought it was a can of Pepsi, so I decided against it.

Since then I've been sent the article (or various summaries and commentaries) four times, along with the questions "can you tell me more about this?" and "should I be freaking out right now?"  So I guess there's enough interest (and concern) over this that it's worth a post.

The answer to the second question, at least, is "No, not yet;" and as for the first, here goes.

The issue has to do with a property of a great many organic molecules called chirality.  Chirality is like the handedness of a pair of gloves; no matter how you flip or turn a left-handed glove, it's not going to fit on your right hand.  It's made of the same parts, but put together in such a way that it can't be rotated or translated to coincide with its opposite.  Pairs of molecules like that are called enantiomers or optical isomers (the latter because crystals made of them rotate polarized light in opposite directions).

A left-handed and right-handed enantiomer of an amino acid [Image is the Public Domain courtesy of NASA]

The key point here is that on Earth, living things generally can only synthesize and metabolize one form of chiral molecules; our amino acids are all left-handed, while our sugars (including the ones in the backbones of DNA and RNA) are right-handed.  Given a diet of food made of right-handed amino acids and left-handed sugars, we'd probably not notice a difference in taste or texture -- but since our enzymes are all evolved to deal with a particular handedness, the food wouldn't be metabolizable.

In short, we'd starve to death.

The article in Science deals with the fact that biochemists have been working to find out if it's possible to create "mirror life" -- organisms constructed of molecules with the opposite handedness as our own.  And this is what has some people concerned.  The authors write:

Driven by curiosity and plausible applications, some researchers had begun work toward creating lifeforms composed entirely of mirror-image biological molecules.  Such mirror organisms would constitute a radical departure from known life, and their creation warrants careful consideration.  The capability to create mirror life is likely at least a decade away and would require large investments and major technical advances; we thus have an opportunity to consider and preempt risks before they are realized.  Here, we draw on an in-depth analysis of current technical barriers, how they might be eroded by technological progress, and what we deem to be unprecedented and largely overlooked risks.  We call for broader discussion among the global research community, policy-makers, research funders, industry, civil society, and the public to chart an appropriate path forward.

The main concern is that if these mirror organisms were somehow to escape from the lab, we wouldn't have much of a way to fight back.  Both antibodies and antibiotics are chiral as well, and likely wouldn't recognize and bind to organisms whose cell surfaces were made of molecules with the opposite handedness.  Any of these synthetic organisms that did turn out to be pathogenic would require a whole different suite of medications, and our own bodily defenses would likely be relatively useless against them.

But.

Here's the thing.  If the scientists do succeed in creating mirror life, and it does escape, the most likely result would be... nothing.  Mirror life would itself need food, and of the proper handedness for its own enzymes; and given that everything in the environment has the same left-handed amino acids and right-handed sugars that we do, these synthetic life forms would have nothing to eat.  The only possible problem would be if the scientists created a mirror autotroph -- something capable of synthesizing its own nutrients, like cyanobacteria, algae, or plants.  Then, it could be a problem, from the standpoint that like exotic invasives, it would have no natural predators and might outcompete other organisms in its environment.

The other concern, though, is the "life finds a way" thing.  A mutation allowing one of these synthetic organisms to metabolize proteins or sugars of the opposite handedness from their own (or both of them) would be at a distinct advantage; if we created one of those, and it escaped, we might well be fucked.  The thing is, from what we know of biochemistry, that's an extremely rare adaptation.  I only know of one organism -- a rather obscure plant pathogen called Burkholderia caryophyllii -- that has an enzyme called D-threo-aldose 1-dehydrogenase that allows it to oxidize left-handed glucose.  

But unless you're a carnation, Burkholderia isn't a threat.

So that's an awful lot of ifs.  Thus my response that you don't have anything pressing to worry about from this research.

Now, mind you, I'm all for being careful, and I mean no criticisms of the scientists who are advising cautious consideration.  We have a rather abysmal track record of launching into stuff without thinking about the consequences.  But as far as whether we ordinary laypeople need to be worried about some synthetic mirror-image pathogen attacking next Tuesday and reducing us all to little quivering blobs of goo, I'd say no.

On the other hand, I'm the guy who told his AP Biology students in January of 1997 that "adult tissue cloning is at least ten years away," exactly one month before the announcement about Dolly the Sheep.  So maybe any predictions I make should be taken with a grain of salt.

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Hand-in-glove

One of the more fascinating bits of biochemistry is the odd "handedness" (technically called chirality) that a lot of biological molecules have.  Chiral molecules come in a left-handed (sinistral) and a right-handed (dextral) form that are made of exactly the same parts but put together in such a way that they're mirror-images of each other, just like a left-handed and right-handed glove.

Where it gets really interesting is that although the left-handed and right-handed forms of biologically active molecules have nearly identical properties, they aren't equivalent in function within living cells.  Nearly all naturally-occurring sugars are right-handed (that's where the name dextrose comes from); amino acids, on the other hand, are all left-handed (which is why amino acid supplements often have an "l-" in front of the name -- l-glutamate, l-tryptophan, and so on).  Having evolved with this kind of specificity has the result that if you were fed a mirror-image diet -- left-handed glucose, for example, and proteins made of right-handed amino acids -- you wouldn't be able to tell anything apart by its smell or taste, but you would proceed to starve to death because your cells would not be able to metabolize molecules with the wrong chirality.

Chirality in amino acids [Image is in the Public Domain courtesy of NASA]

Molecular chirality was used to brilliant effect by the wonderful murder mystery author Dorothy Sayers in her novel The Documents in the Case.  In the story, a man dies after eating a serving of mushrooms he'd picked.  His friends and family are stunned; he'd been a wild mushroom enthusiast for decades, and the fatal mistake he apparently made -- including a deadly ivory funnel mushroom (Clitocybe dealbata) in with a pan full of other edible kinds -- was something they believed he never would have done.

The toxic substance in ivory funnels, the alkaloid muscarine, is -- like many organic compounds -- chiral.  Naturally-occurring muscarine is all left-handed.  However, when it's synthesized artificially in the lab, you end up with a mixture of right- and left-handed molecules, in about equal numbers.  So when the contention is made that the victim hadn't mistakenly included a poisonous mushroom in with the edible ones, but had been deliberately poisoned by someone who'd added the chemical to his food, the investigators realize this is the key to solving the riddle of the man's death.

Chiral molecules have another odd property; if you shine a beam of polarized light through a crystal, right-handed ones rotate the polarization angle of the beam clockwise, and left-handed ones counterclockwise.  So when an extract from the victim's digestive tract is analyzed, and a polarized light beam shined through it splits in two -- part of the beam rotated clockwise, the other part counterclockwise -- there's no doubt he was poisoned by synthetic (mixed-chiral) muscarine, not by mistakenly eating a poisonous mushroom that would only have contained the left-handed form.

So specific chirality is ubiquitous in the natural world.  We have a particular handedness, all the way down to the molecular level.  What's a little puzzling, however, is why this tendency occurs.  Not chirality per se; that merely arises from the fact that if you bond four different atoms or groups around a central carbon atom, there are two ways you can do it, and they result in molecules that are mirror images of each other (as shown in the image above).  But why do living things all exhibit a preference for a certain handedness?  It must have evolved extremely early, because virtually all living things share the same preferences.  But what got this bias started -- especially given that left-handed and right-handed molecules are equally easy to make abiotically, and have nearly identical physical and chemical properties?

Well, a paper this week in the journal Advanced Materials may have just answered this long-standing question.  A group led by Karl-Heinz Ernst, at the Swiss Federal Laboratories for Materials Science and Technology, found that the selection for a particular handedness happened because of the interplay between the electromagnetic fields of metallic surfaces with the spin configuration of chiral molecules.

They created surfaces coated with patches of a thin layer of a magnetic metal, such as iron or cobalt, and analyzed the magnetic "islands" to determine the direction of orientation of the magnetic field of each.  They then took a solution of a chiral molecule called helicene, which had equal numbers of right and left-handed forms, and poured it over the surface.  The hypothesis was that the opposite patterns of spin of the electrons in the two different forms of helicene would allow them to bond only to a magnetic patch with a specific orientation. 

So after introducing the mixed helicene to the metal surfaces, they looked to see where the molecules adhered.

Sure enough -- depending on the direction of the magnetic field, one or the other form of helicene stuck to the metal surface.  The magnetic field was acting as a selecting agent on the spin, picking out the handedness that was compatible with the orientation of the patch.

This, of course, is only a preliminary study of a single chiral molecule in a very artificial setting.  However, it does for the first time provide a mechanism by which selective chirality could have originated.  "In certain surface-catalyzed chemical reactions," Ernst explained, "such as those that could have taken place in the chemical 'primordial soup' on the early Earth, a certain combination of electric and magnetic fields could have led to a steady accumulation of one form or another of the various biomolecules -- and thus ultimately to the handedness of life."

So a simple experiment (simple to explain, not to perform!) has taken the first step toward settling a question that chemistry Nobel laureate Vladimir Prelog called "one of the first questions of molecular theology" back in 1975.  It shows that science has the capacity for reaching back and explaining the earliest origins of biochemistry -- and how life as we know it came about.

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Hand-in-glove

One of the more fascinating bits of biochemistry is the odd "handedness" (technically called chirality) that a lot of biological molecules have.  Chiral molecules come in a left-handed (sinistral) and a right-handed (dextral) form that are made of exactly the same parts but put together in such a way that they're mirror-images of each other, just like a left-handed and right-handed glove.

Where it gets really interesting is that although the left-handed and right-handed forms of biologically active molecules have nearly identical properties, they aren't equivalent in function.  Nearly all naturally-occurring sugars are right-handed; amino acids, on the other hand, are all left-handed.  No one knows why this is, but having evolved with this kind of specificity has the result that if you were fed a mirror-image diet -- left-handed glucose, for example, and proteins made of right-handed amino acids -- you wouldn't be able to tell anything apart by its smell or taste, but you would proceed to starve to death because your cells would not be able to metabolize molecules with the wrong chirality.

Chirality in amino acids [Image is in the Public Domain courtesy of NASA]

Molecular chirality was used to brilliant effect by the wonderful murder mystery author Dorothy Sayers in her novel The Documents in the Case.  In the story, a man dies after eating a serving of mushrooms he'd picked.  His friends and family are stunned; he'd been a wild mushroom enthusiast for decades, and the fatal mistake he apparently made -- including a deadly ivory funnel mushroom (Clitocybe dealbata) in with a pan full of other edible kinds -- was something he never would have done.

The toxic substance in ivory funnels, the alkaloid muscarine, is -- like many organic compounds -- chiral.  Naturally-occurring muscarine is all left-handed.  However, when it's synthesized in the lab, you end up with a mixture of right- and left-handed molecules, in about equal numbers.  So when the contention is made that the victim hadn't mistakenly included a poisonous mushroom in with the edible ones, but had been deliberately poisoned by someone who'd added the chemical to his food, the investigators realize this is the key to solving the riddle of the man's death.

Chiral molecules have another odd property; if you shine a beam of polarized light through a crystal, right-handed ones rotate the polarization angle of the beam clockwise, and left-handed ones counterclockwise.  So when an extract from the victim's digestive tract is analyzed, and a polarized light beam shined through it splits in two -- part of the beam rotated clockwise, the other part counterclockwise -- there's no doubt he was poisoned by synthetic muscarine, not by mistakenly eating a poisonous mushroom.

Turns out there may be a way to use this hand-in-glove property of biological molecules not to solve a murder, but to detect life on other planets.  As with Dorothy Sayers's synthetic muscarine, organic compounds not produced by a living thing would almost certainly be a mixture of the two chiralities, right- and left-handed.  Because organisms here on Earth are all so incredibly specific about which chirality they need (or create), it's a fair guess that living things on other worlds would have the same choosiness.  And now a technique has been developed to detect molecular chirality in the light reflected from a forest from two kilometers away, by a spectropolarimeter on a helicopter flying at seventy kilometers per hour.

It only took seconds for the detector to tell the difference between light reflected from a living thing and light reflected from something inanimate, like a rock face or an asphalt road.  Now that we're becoming increasingly good at seeing the faint light reflected from the surface of exoplanets, looking for rotation of the polarization angle of that light might be a quick way to see if there's anything alive down there.

"The next step we hope to take is to perform similar detections from the International Space Station (ISS), looking down at the Earth," said astrophysicist Brice-Olivier Demory of the University of Bern and MERMOZ (Monitoring planEtary suRfaces with Modern pOlarimetric characteriZation).  "That will allow us to assess the detectability of planetary-scale biosignatures.  This step will be decisive to enable the search for life in and beyond our Solar System using polarization."

Which is really cool, although as an aside someone needs to explain to whoever is in charge of MERMOZ how acronyms work.

In any case, the whole idea is brilliant, and the possibility that we could detect living organisms on a distant planet just by analyzing the reflected light polarization is mind-boggling.  It's long been the stumbling block in the search for extraterrestrial life; if a planet hosts life, but the living things there are pre-technological, how would we know they're there?  After all, as little as two centuries ago, intelligent aliens would have detected no radio signals coming from Earth, and (of course) we wouldn't have had the capability of detecting any they sent us.

But now, maybe we can tell if there's something alive out there without it having to communicate with us directly.  Like Dorothy Sayers's intrepid detectives, all we have to do is see if the light twists in only one direction, and it might well be case closed.

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One of the most devastating psychological diagnoses is schizophrenia.  United by the common characteristic of "loss of touch with reality," this phrase belies how horrible the various kinds of schizophrenia are, both for the sufferers and their families.  Immersed in a pseudo-reality where the voices, hallucinations, and perceptions created by their minds seem as vivid as the actual reality around them, schizophrenics live in a terrifying world where they literally can't tell their own imaginings from what they're really seeing and hearing.

The origins of schizophrenia are still poorly understood, and largely because of a lack of knowledge of its causes, treatment and prognosis are iffy at best.  But much of what we know about this horrible disorder comes from families where it seems to be common -- where, apparently, there is a genetic predisposition for the psychosis that is schizophrenia's most frightening characteristic.

One of the first studies of this kind was of the Galvin family of Colorado, who had ten children born between 1945 and 1965 of whom six eventually were diagnosed as schizophrenic.  This tragic situation is the subject of the riveting book Hidden Valley Road: Inside the Mind of an American Family, by Robert Kolker.  Kolker looks at the study done by the National Institute of Health of the Galvin family, which provided the first insight into the genetic basis of schizophrenia, but along the way gives us a touching and compassionate view of a family devastated by this mysterious disease.  It's brilliant reading, and leaves you with a greater understanding of the impact of psychiatric illness -- and hope for a future where this diagnosis has better options for treatment.

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

 

In your right mind

There's a peculiarity of the human brain called lateralization, which is the tendency of the brain to have a dominant side.  It's most clearly reflected in hand dominance; because of the cross-wiring of the brain, people who are right-handed have a tendency to be left brain dominant, and vice versa.  (There's more to it than that, as some people who are right handed are, for example, left eye dominant, but handedness is the most familiar manifestation of brain lateralization.)

It bears mention at this juncture that the common folk wisdom that brain lateralization has an influence on your personality -- that, for instance, left brain dominant people are sequential, mathematical, and logical, and right brain dominant people are creative, artistic, and holistic -- is complete nonsense.  That myth has been around for a long while, and has been roundly debunked, but still persists for some reason.

I first was introduced to the concept of brain dominance when I was in eighth grade.  I was having some difficulty reading, and my English teacher, Mrs. Gates, told me she thought I was mixed-brain dominant -- that I didn't have a strongly lateralized brain -- and that this often leads to processing disorders like dyslexia.  (She was right, but they still don't know why that connection exists.)  It made sense.  When I was in kindergarten, I switched back and forth between writing with my right and left hand about five times until my teacher got fed up and told me to simmer down and pick one.  I picked my right hand, and have stuck with it ever since, but I still have a lot of lefty characteristics.  I tend to pick up a drinking glass with my left hand, and I'm strongly left eye dominant, for example.

Anyhow, Mrs. Gates identified my mixed-brainness, and the outcome apropos of my reading facility, but she also told me that there was one thing that mixed-brain people can learn faster than anyone else.  Because of our nearly-equal control from both sides of the brain, we can do a cool thing, which Mrs. Gates taught me and I learned in fifteen seconds flat.  I can write, in cursive, forward with my right hand while I'm writing the same thing backwards with my left.  (Because it's me, they're both pretty illegible, but it's still kind of a fun party trick.)

[Image licensed under the Creative Commons Evan-Amos, Human-Hands-Front-Back, CC BY-SA 3.0]

Fast forward to today.  It's been known for years that lots of animals are lateralized, so it stands to reason that it must confer some kind of evolutionary advantage, but what that might be was unclear until recently.

Research by a team led by Onur Güntürkün, of the Institute of Cognitive Neuroscience at Ruhr-University Bochum, in Germany, has looked at lateralization in animals from cockatoos to zebra fish to humans, and has described the possible evolutionary rationale for having a dominant side of the brain.

"What you do with your hands is a miracle of biological evolution," Güntürkün says. " We are the master of our hands, and by funneling this training to one hemisphere of our brains, we can become more proficient at that kind of dexterity.  Natural selection likely provided an advantage that resulted in a proportion of the population -- about 10% -- favoring the opposite hand.  The thing that connects the two is parallel processing, which enables us to do two things that use different parts of the brain at the same time."

Additionally, Güntürkün says, our perceptual systems have also evolved that kind of division of labor.  Both left and right brain have visual recognition centers, but in humans the one on the right side is more devoted to image recognition, and the one on the left to word and symbol recognition.  And this is apparently a very old evolutionary innovation, long predating our use of language; even pigeons have a split perceptual function between the two sides of the brain (and therefore between their eyes).  They tend to tilt their heads so their left eye is scanning the ground for food while their right one scans the sky for predators.

So what might seem to be a bad idea -- ceding more control to one side of the brain than the other, making one hand more nimble than the other --turns out to have a distinct advantage.  And if you'll indulge me in a little bit of linguistics geekery, for good measure, even our word "dexterous" reflects this phenomenon.  "Dexter" is Latin for "right," and reflects the commonness of right-handers, who were considered to be more skillful.  (And when you find out that the Latin word for "left" is "sinister," you get a rather unfortunate lens into attitudes toward southpaws.)

Anyhow, there you have it; another interesting feature of our brain physiology explained, and one that has a lot of potential for increasing our understanding of neural development.  "Studying asymmetry can provide the most basic blueprints for how the brain is organized," Güntürkün says.  "It gives us an unprecedented window into the wiring of the early, developing brain that ultimately determines the fate of the adult brain.  Because asymmetry is not limited to human brains, a number of animal models have emerged that can help unravel both the genetic and epigenetic foundations for the phenomenon of lateralization."

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I've always been in awe of cryptographers.  I love puzzles, but code decipherment has seemed to me to be a little like magic.  I've read about such feats as the breaking of the "Enigma" code during World War II by a team led by British computer scientist Alan Turing, and the stunning decipherment of Linear B -- a writing system for which (at first) we knew neither the sound-to-symbol correspondence nor even the language it represented -- by Alice Kober and Michael Ventris.

My reaction each time has been, "I am not nearly smart enough to figure something like this out."

Possibly because it's so unfathomable to me, I've been fascinated with tales of codebreaking ever since I can remember.  This is why I was thrilled to read Simon Singh's The Code Book: The Science of Secrecy from Ancient Egypt to Quantum Cryptography, which describes some of the most amazing examples of people's attempts to design codes that were uncrackable -- and the ones who were able to crack them.

If you're at all interested in the science of covert communications, or just like to read about fascinating achievements by incredibly talented people, you definitely need to read The Code Book.  Even after I finished it, I still know I'm not smart enough to decipher complex codes, but it sure is fun to read about how others have accomplished it.

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

The left-handed universe

I first ran into the concept of chirality when I was a fifteen-year-old Trekkie science fiction nerd.

I grew up watching the original Star Trek, which impressed the hell out of me as a kid even though rewatching some of the episodes now generates painful full-body cringes at the blatant sexism and near-jingoistic chauvinism.  Be that as it may, after going through the entire series I don't even know how many times, I started reading some of the fan fiction.

The fan fiction, of course, was more uneven than the show had been.  Some of it was pretty good, some downright terrible.  One that had elements of both, putting it somewhere in the "fair to middling" category, was Spock Must Die by James Blish.  Blish had gotten into the Star Trek universe writing short-story adaptations of most of the original series episodes, but this one was entirely new.

Well, mostly.  It springboarded off an original series episode, "Errand of Mercy," in which the Federation and the Klingons are fighting over the planet Organia, which is populated by a peaceful, pastoral society.  Kirk et al. are trying to stop the Klingons from massacring the Organians, but much to Kirk's dismay, the Organians refuse Federation protection, insisting they don't need any help.  And it turns out they don't -- in the end, you find out that the Organians are super-powerful aliens who only assumed human-ish form to communicate with the two humanoid invading forces, and are so far beyond both of them that they indeed had nothing to fear.

In Spock Must Die, the crew of the Enterprise is sent to investigate why Organia has suddenly gone radio-silent.  It turns out that the Klingons have surrounded the entire planet with a force field.  Spock volunteers to try to transport through it, which fails -- but after the attempt, suddenly there are two Spocks in the transporter room, each claiming to be the real, original Vulcan.

[spoiler alert, if anyone is actually going to go back and read it...]  What happened is that the transporter beam was reflected off the surface of the force field, and it duplicated Spock -- there was the original (who never left the transporter pad) and the duplicate (the reflection, recreated in place).  Since both the original and the duplicate were identical down to the last neuron, each of them had the same memories, and each was convinced he was the real Spock.

The key turned out to be the fact that the duplicate had been reflected all the way down to the molecular level.

Why this matters is that a number of molecules in our bodies -- amino acids and sugars being two common examples -- are chiral, meaning they have a "handedness."  Just like a glove, they exist in two possible forms, a "right-handed" and a "left-handed" one, which are mirror images of each other.  And for reasons unknown, all of our amino acids are left-handed.  No organism known manufactures right-handed amino acids.  Further, if you synthesized right-handed amino acids -- which could be done in the laboratory -- and fed them to a terrestrial organism, the organism would starve.

But the reflected Spock, of course, is exactly the opposite.  Kirk eventually figures out what's happened because one of the Spocks barricades himself in one of the science laboratories, claiming the other Spock wants to kill him.  The truth was he had to have access to a lab in order to synthesize the right-handed amino acids without which he'd die.

Clever concept for a story, right there.

[Image licensed under the Creative Commons Petritap, Finnish mittens, CC BY-SA 3.0]

Chirality is quite a mystery.  Like I said, the left-handedness of amino acids is shared by all known terrestrial organisms, so that bias must have happened very early in the generation of life.

Why it happened is another matter entirely.  A persistent question in scientific inquiries into the origin of life on Earth (and the possibility of life elsewhere) is how much of our own biochemistry and metabolism is constrained.  We code our genetic information as DNA; could it be done a different way elsewhere?  Our primary energy driver is ATP.  Are there other ways organisms might store and access chemical energy?  The question of constraint goes all the way up the scale to macroscopic features, such as cephalization -- the clustering of the sensory processing organs near the anterior end of the animal.  Makes sense; you want your sensors facing (1) the direction you're traveling, and (2) what you're eating.  But are there other equally sensible ways to put an animal together?

Some things we take for granted almost certainly aren't constrained, like bilateral symmetry.  So many animals are bilaterally symmetrical that the ones that aren't (like adult flounders) stand out as bizarre.  Aficionados of H. P. Lovecraft might remember that amongst the innovative ideas he used was that the aliens in "At the Mountains of Madness" weren't bilateral, but had five-way symmetry -- something completely unknown on Earth.  (You may be thinking, "wait... starfish?"  Starfish have what I'd call pseudo-pentaradial symmetry.  As larvae, they're clearly bilateral, and they lose a lot of bilateral features when they mature.  But some characteristics -- like the position of the sieve plate, their water-intake device -- give away that deep down, they are still basically bilateral.)

Anyhow, all this comes up because of a recent discovery by astrobiologists at NASA's Goddard Space Flight Center.  In a press release, we hear about a meteorite discovered in Antarctica called Asuka 12236, which is a carbonaceous chondrite -- a peculiar type of meteorite that is rich in organic compounds.  Asuka 12236 contained large quantities of amino acids, which isn't as bizarre as it sounds; amino acids have been shown to form relatively easily if there are raw materials and a source of energy.

What stands out is that all of the amino acids in Asuka 12236 are left-handed -- just like the ones on Earth.

The scientists studying the meteorite are up front that the first thing to do is rule out that the amino acids in the meteorite aren't contaminants absorbed after the rock crash-landed.  Most of the experts, however, think this is unlikely, and that we're looking at a genuine sample of extraterrestrial amino acids.  And the fact that they all show left-handed chirality is pretty remarkable -- suggesting that the chirality of our biochemicals might, in fact, be constrained, and that we could well find biochemistry similar to our own on other planets.

In that way, at least.

So that's one less thing to worry about if we ever go to an alien world.  Unlike the right-handed reflected Mr. Spock, we'd be able to metabolize alien amino acids just fine.

Of course, how familiar-looking everything else would be is still open to question.

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This week's Skeptophilia book recommendation of the week is a brilliant retrospective of how we've come to our understanding of one of the fastest-moving scientific fields: genetics.

In Siddhartha Mukherjee's wonderful book The Gene: An Intimate History, we're taken from the first bit of research that suggested how inheritance took place: Gregor Mendel's famous study of pea plants that established a "unit of heredity" (he called them "factors" rather than "genes" or "alleles," but he got the basic idea spot on).  From there, he looks at how our understanding of heredity was refined -- how DNA was identified as the chemical that housed genetic information, to how that information is encoded and translated, to cutting-edge research in gene modification techniques like CRISPR-Cas9.  Along each step, he paints a very human picture of researchers striving to understand, many of them with inadequate tools and resources, finally leading up to today's fine-grained picture of how heredity works.

It's wonderful reading for anyone interested in genetics and the history of science.

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