Scattered to the winds

One of the more puzzling aspects of evolutionary theory is the phenomenon of peripheral isolates.

This term refers to widely-separated populations of seemingly closely-related organisms.  One of the first times I ran into this phenomenon came to my attention because of my obsession with birdwatching.  There's a tropical family of birds called trogons, forest-dwelling fruit-eaters that are prized by birdwatchers for their brilliant colors.  There are trogons in three places in the world... Central and South America (27 species), central Africa (3 species), and southern Asia (11 species).

These are very far apart.  But take a look at three representatives from each group -- it doesn't take an ornithologist to see that they've got to be closely related:

The Elegant Trogon (Trogon elegans) of Central America [Image licensed under the Creative Commons dominic sherony, Elegant Trogon, CC BY-SA 2.0]

The Narina Trogon (Apaloderma narina) of central Africa [Image licensed under the Creative Commons Derek Keats from Johannesburg, South Africa, Narina Trogon, Apaloderma narina MALE at Lekgalameetse Provincial Reserve, Limpopo, South Africa (14654439002), CC BY 2.0]

The Red-headed Trogon (Harpactes erythrocephalus) of southeast Asia [Image licensed under the Creative Commons JJ Harrison (jjharrison89@facebook.com), Harpactes erythrocephalus - Khao Yai, CC BY-SA 3.0]

I know, I just had a post this week about how misleading morphology/appearance can be in determining relationships, but you have to admit these are some pretty convincing similarities.

The question, of course, is how did this happen?  Where did the group originate, and how did members end up so widely separated?  To add to the puzzle, the fossil record for the group indicates that in the Eocene Epoch, fifty-ish million years ago, there were trogons in Europe -- fossils have been found in Denmark and Germany -- and the earliest fossil trogons from South America come from the Pleistocene Epoch, only two million years ago.

So are these the remnants of what was a much larger and more widespread group, whose northern members perhaps succumbed due to one of the ice ages?  Did they start in one of their homelands and move from there?

And if that's true, why are there no examples of trogons from all the places in between?

Another example of this is the order of mammals we belong to (Primata).  Primates pretty clearly originated in Africa and spread from there; the earliest clear primates were in the Paleocene Epoch, on the order of sixty million years ago, but the ancestor of all primates was probably at least twenty million years before that, preceding the Cretaceous Extinction by fourteen million years.  From their start in east Africa they seem to have spread both east and west, reaching southeast Asia around fifty million years ago.  Some of the earliest members to split were the lorises and tarsiers that I wrote about on Tuesday, along with the lemurs of Madagascar.

But the next group to diverge -- and the reason the whole topic of peripheral isolates came up -- are the "New World monkeys," the "platyrhines" of Central and South America.  It looks like this split happened during the Oligocene Epoch, around thirty million years ago... but how?

At that point, Africa was separated from South America by nine hundred miles of ocean -- narrower than the Atlantic is today, but still a formidable barrier.  But a paper in Science this week describes recently-discovered evidence from Peru of some fossilized primate teeth from right around the time the New World/Old World monkey split happened.

What this discovery suggests is staggering; all of the New World monkeys, from the spider monkey to the black howler monkey to the Amazonian pygmy marmoset, are descended from a single group that survived a crossing of the Atlantic, probably on a vegetation raft torn loose in a storm, only a little over thirty million years ago.

"This is a completely unique discovery," said Erik Seiffert, the study's lead author and Professor of Clinical Integrative Anatomical Sciences at Keck School of Medicine of the University of Southern California, in an interview with Science Daily.  "We're suggesting that this group might have made it over to South America right around what we call the Eocene-Oligocene Boundary, a time period between two geological epochs, when the Antarctic ice sheet started to build up and the sea level fell.  That might have played a role in making it a bit easier for these primates to actually get across the Atlantic Ocean."

So here we have a possible explanation for one of the long-standing puzzles of evolutionary biology.  Note that these puzzles aren't a weakness of the theory; saying "we still have some things left to explain" isn't the same as saying "the theory can't explain this."  There will always be pieces to add and odd bits of data to account for, but I have 100% confidence that the evolutionary model is up to the task.

Now, I wish it could just come with an explanation for the trogons, because for some reason that really bothers me.

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This week's Skeptophilia book recommendation of the week is brand new -- only published three weeks ago.  Neil Shubin, who became famous for his wonderful book on human evolution Your Inner Fish, has a fantastic new book out -- Some Assembly Required: Decoding Four Billion Years of Life, from Ancient Fossils to DNA.

Shubin's lucid prose makes for fascinating reading, as he takes you down the four-billion-year path from the first simple cells to the biodiversity of the modern Earth, wrapping in not only what we've discovered from the fossil record but the most recent innovations in DNA analysis that demonstrate our common ancestry with every other life form on the planet.  It's a wonderful survey of our current state of knowledge of evolutionary science, and will engage both scientist and layperson alike.  Get Shubin's latest -- and fasten your seatbelts for a wild ride through time.

The unbalanced universe

In her brilliant 2011 TED Talk "On Being Wrong," journalist Kathryn Schulz said, "For good and for ill, we generate these incredible stories about the world around us, and then the world turns around and astonishes us."

That astonishment is at the root of scientific discovery.  Many laypeople have the sense that scientists do what they do by patiently adding data bit by bit, assembling a theory from the results of experiment -- less understood is the fact that much of the time, the experiments themselves happened because of something unexpected that the old model couldn't explain.  It's those moments of, "Hey, now, wait a moment..." that have generated some of the most fundamental theories we have -- universal gravitation, relativity (special and general), evolution, genetics, plate tectonics.

Or, as another luminary of the philosophy of science put it -- James Burke, in his brilliant documentary series The Day the Universe Changed -- "The so-called voyage of discovery has, as often as not, made landfall for reasons little to do with the search for knowledge...  As far as one discovery following another along the way as part of some grand plan, what way?  Going where?"

Now, this is not to say that the lazy student's complaint, "why should we learn science, since it could all be proven wrong tomorrow?", has much merit.  The big ideas, like the ones I listed before, have been so extensively tested that it's unlikely they'll change much.  Any refinements will most probably be on the level of details.  Still... those head-scratching moments do occur, and sometimes they result in an overturning of what we thought we understood -- like the observation that was announced this week from NASA's Chandra X-ray Observatory.

[Image courtesy of NASA/Harvard University/Chandra X-ray Observatory]

One of the basic pieces of the Big Bang theory is that it resulted in a universe that is isotropic -- it basically looks the same no matter which direction you're looking.  The idea here is that when the universe began to expand, the fabric of space/time stretched out so much in the first tiny fraction of a second (something called cosmological inflation) that it resulted in a uniform, isotropic universe.

The analogy that's been around a long time to explain this -- I remember my college astronomy teacher using it, back in the early 1980s -- is to picture yourself as a tiny person, standing on one dot of a deflated polka-dotted balloon.  If the balloon is inflated, you see all the other dots moving away from you, regardless of which dot you're standing on; and in every direction, the dot-density is pretty much the same.  "There is no center of the universe," I recall our professor, Dr. Daniel Whitmire, saying.  "Or, perhaps, everywhere is the center.  It means essentially the same thing."

So the idea of isotropy is pretty deeply built into the Big Bang cosmology.  So the observation from Chandra announced this week that the universe seems to be anisotropic was a little startling, to say the least.

"Based on our cluster observations we may have found differences in how fast the universe is expanding depending on which way we looked," said study co-author Gerrit Schellenberger of the Center for Astrophysics of Harvard University.  "This would contradict one of the most basic underlying assumptions we use in cosmology today."

Or, as Konstantinos Migkas of the University of Bonn in Germany, who led the new study, put it, "One of the pillars of cosmology... is that the universe is 'isotropic....'   Our work shows there may be cracks in that pillar."

It's possible that the measurement doesn't mean what it seems to mean.  One possibility the researchers came up with that would be less-than-earthshattering is that some of the distant clusters might be moving together because of the gravitational pull of an unseen massive object or objects, throwing off the data enough to make it look like an anisotropy.  Another possibility -- which in my mind raises more questions than it solves -- is that the hypothesized "dark energy" that makes up three-quarters of the energy density of the universe is unevenly distributed, meaning its repulsive force is greater in some places than in others.  "This would be like if the yeast in the bread isn't evenly mixed, causing it to expand faster in some places than in others," said study co-author Thomas Reiprich, also of the University of Bonn, adding, "It would be remarkable if dark energy were found to have different strengths in different parts of the universe."

Remarkable especially since we still basically have no idea what dark energy is.  Going from there to any kind of cogent explanation of why there's more of it here than there seems to me to be a significant leap.

Or, perhaps, none of those is correct, and the anisotropy was built-in at the moment of the Big Bang by some process we haven't even dreamed of.

Whatever it turns out to be, this seems to me to be one of those "wait a moment..." discoveries that could potentially lead to a major revision of what we thought we knew.  What's certain is that it demonstrates how far we have to go in science -- and despite our progress, to paraphrase Kathryn Schulz, the universe will time after time turn around and astonish us.

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This week's Skeptophilia book recommendation of the week is brand new -- only published three weeks ago.  Neil Shubin, who became famous for his wonderful book on human evolution Your Inner Fish, has a fantastic new book out -- Some Assembly Required: Decoding Four Billion Years of Life, from Ancient Fossils to DNA.

Shubin's lucid prose makes for fascinating reading, as he takes you down the four-billion-year path from the first simple cells to the biodiversity of the modern Earth, wrapping in not only what we've discovered from the fossil record but the most recent innovations in DNA analysis that demonstrate our common ancestry with every other life form on the planet.  It's a wonderful survey of our current state of knowledge of evolutionary science, and will engage both scientist and layperson alike.  Get Shubin's latest -- and fasten your seatbelts for a wild ride through time.

The attentional window

One of the critical functions of our brain, and one that we don't often think about, is its ability to determine quickly what stimuli are important to pay attention to, and which can safely be ignored.

Which is not to say that it always gets things right.  There have been a number of fascinating experiments run on inattentional blindness, our complete lack of awareness of something we saw, presumably because the brain thought other stuff it was witnessing was more important.  You've probably heard about the most famous inattentional blindness experiment -- the video clip with a half-dozen people tossing around balls, where the instructions were (for example) to count the number of times a person in a black shirt caught a red ball -- and test subjects literally did not see the person in the gorilla suit who walked out into the middle of the scene, pounded his chest a few times, then walked off.

Even more curious is a less-known experiment where a table was set up in a hotel lobby, with one of the researchers sitting behind it (and a tablecloth over the table and down the front, obscuring what was happening underneath).  The researcher asked passersby if they'd mind taking a survey, and when he got a "yes" he handed them a clipboard, then "accidentally" dropped the pencil.  He ducked down to pick up the pencil -- then slipped under the table, and a completely different person came back up with the pencil.  No facial similarities at all.

Not only did virtually no one hesitate at all when the pencil was handed to them -- no reaction whatsoever -- when questioned afterward, a number of the test subjects claimed the researchers were lying about the switcheroo, even after seeing that there were two researchers behind the table who looked nothing alike.

By far my favorite, though, is the short video called "Whodunnit?" that was put together to increase public awareness of how inattentive and distractible we are (in the context of driving safely).  I won't clue you in about what's going on, but if you haven't seen it, take a look.  If you're anything like me, you'll spend the second half of the video with your mouth hanging open in astonishment.

So our brains aren't perceiving everything around us.  Far from it.  There's a filter applied to everything we sense, and the brain is the ultimate arbiter of what it deems important enough to notice and/or remember.  This is at least partly responsible for the experience I suspect we've all had, of having yourself and a friend describe an event and finding out that you and (s)he recall completely different parts of it.

This all comes up because of some research done at the National Eye Institute, published this week in the Journal of Neuroscience, that shows -- at least if human sensory/perceptive systems work like those of mice -- that there's a tenth of a second window during which your brain has to decide something's important, and if that window is missed, the stimulus is simply ignored.

A team made up of Lupeng Wang, Kerry McAlonan, Sheridan Goldstein, Charles R. Gerfen, and Richard J. Krauzlis took mice that had been genetically engineered to have cells that were switchable using a laser, and turned off some neurons in a region of the brain called the superior colliculus that is known to have a role in mammalian visual processing.  The switching mechanism was extremely fast and precise, allowing researchers to time the activity of the cells with astonishing accuracy.  They found that if the cells in the superior colliculus were turned off for a tenth of a second following a visual stimulus, the mouse acted as if it hadn't seen the stimulus at all.

So it looks like (again, if we can generalize a mouse model to a human brain) we may have an explanation for the invisible gorilla and the survey-switcheroo; our brains have a vanishingly short window in which to say "hey, this is important, pay attention!"  If that window passes, we're likely not to notice what's right in front of us.  Obviously, the mechanism works well enough.  It enabled our ancestors to notice their environment sufficiently well to avoid danger and respond quickly to threats.  But what it means is that once again, we're left with the rather unsettling conclusion that what we experience (and remember) is incomplete and inaccurate no matter how much we try to pay attention.  Even if you're concentrating, there are going to be some stimuli about which your superior colliculus says, "Meh, that's not important," and you just have to hope that most of the time, it makes the right call.

Me, I'm still wondering how I missed all that stuff in Lord Smythe's living room.  I guess my superior colliculus was really out to lunch on that one.

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This week's Skeptophilia book recommendation of the week is brand new -- only published three weeks ago.  Neil Shubin, who became famous for his wonderful book on human evolution Your Inner Fish, has a fantastic new book out -- Some Assembly Required: Decoding Four Billion Years of Life, from Ancient Fossils to DNA.

Shubin's lucid prose makes for fascinating reading, as he takes you down the four-billion-year path from the first simple cells to the biodiversity of the modern Earth, wrapping in not only what we've discovered from the fossil record but the most recent innovations in DNA analysis that demonstrate our common ancestry with every other life form on the planet.  It's a wonderful survey of our current state of knowledge of evolutionary science, and will engage both scientist and layperson alike.  Get Shubin's latest -- and fasten your seatbelts for a wild ride through time.

The oceans of Europa

On Monday, we looked at some new techniques for detecting exoplanets, and how exciting that is for people like me who are obsessed with extraterrestrial life.  The difficulty, of course, is that even if you find a thousand Earth-like planets in the habitable zone, how could you tell if they're inhabited?  Consider how long the Earth has hosted life (on the order of three billion years) and how long it's been that we've had living things that would be detectible to distant aliens via such signals as radio and television transmissions (on the order of a hundred years).

Life has been present on Earth thirty million times longer than it would be easily detectible to a technological species in another stellar system.

So life could be more or less everywhere out there.  But how could we find it?

The possibilities are limited.  There's been a suggestion that one way is to analyze the atmosphere and look for chemicals like oxygen that are highly reactive and probably wouldn't persist unless there was something (i.e. something living) pumping it in at a constant rate.  But finding planets at a distance is one thing, and analyzing the atmosphere of those planets from something like the faint absorption spectrum lines of the light reflected from the surface, is another thing entirely.

So unless we stumble across a technological society whose signals (deliberate or otherwise) we detect, we could be looking at stupendous biodiversity and never know it.

A different approach is to look for life closer to home.  One of the goals of the Mars rover expeditions was to analyze the soil for the presence of bacterial metabolism, the results of which were equivocal at best.  Venus is out, unless there are life forms that enjoy being in an acidic pressure cooker, which seems unlikely.

But what about the outer planets?

If there is life on the gas giants themselves, it'd have to be unlike anything we have here on Earth.  Carl Sagan hypothesized giant "floaters," creatures like enormous parachutes, that would ride the stormy updrafts of the thick atmosphere and metabolize the methane that makes up a good percentage of it.  But what about the moons?

The moons of the gas giants are possible candidates, as they're small and rocky, and at least some of the larger ones have a stable atmosphere.  The problem is, they're cold.  Ganymede, for example, Jupiter's largest satellite, has a mean surface temperature of about -160 C.

Not exactly your next tropical vacation spot.

But it's not as hopeless as all that, because there's more going on here than meets the eye.  Which brings me to Jupiter's moon Europa.

Europa, showing the cracks in the ice sheet colored by what may be a mix of minerals and organic compounds from the subsurface liquid water ocean [Image is in the Public Domain courtesy of NASA/JPL]

Europa is the smallest of the four "Galilean" moons, so called because they were first observed by Galileo Galilei, which led him afoul of the powers-that-be when he claimed they were orbiting Jupiter (Earth, remember, was thought to be the center of the universe, with everything orbiting around it).  But eppur si muove, as Galileo muttered when he was found guilty of heresy ("and yet it moves"), and the total number of Jovian satellites now stands at 79.

Europa, however, is especially fascinating.  Pioneer 10 and 11, the (aptly-named) Galileo orbiter, and most recently the New Horizons probe, have all brought us back a picture of Europa that's curious to say the least.  It's got a surface made mostly of water ice, but its overall density is consistent with being mostly composed of silicate minerals (so it's a rocky ball underneath its icy covering).  Most interesting, though, is that magnetometer readings support the conclusion that between the two is a layer of ion-rich liquid water on the order of thirty kilometers in depth -- a subsurface sea rich in magnesium, sodium, and calcium, traces of which are found on the surface when the cracking of shifting of the ice sheet allows the seawater to bubble up and freeze onto the surface.

This makes Europa an excellent candidate for hosting life, at least the microbial type.  But what's keeping the water liquid, so far out there in the cold reaches of the Solar System?

Apparently, its host planet is.  Jupiter is enormous, and has Europa tidally locked (the same side faces Jupiter all the time).  Its orbit isn't perfectly circular, though, and as it zips around, tracing out an ellipse, the changes in gravitational pull generate tidal flexing.  The giant planet pulls and distorts the core of the moon, and the friction that creates generates enough heat to keep the subsurface ocean liquid.

So we have something a little analogous to the Earth's hydrothermal vents, albeit powered by a different process.  It means that (though it saddens me to admit) it's probably better to put our money into sending a surface probe to Europa, to look for traces of life frozen onto the surface, than scanning the skies looking for life outside of the Solar System.

We could do both, of course.  That'd make me happy.  But given the budget cuts to NASA in the last few years, they've got to put their time, effort, and money into whatever is going to have the greatest likelihood of working.  At the moment, that looks like the search for extraterrestrial life should focus on our own neighborhood -- starting with a moon that initially looked like a lifeless ball of ice.

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This week's Skeptophilia book recommendation of the week is brand new -- only published three weeks ago.  Neil Shubin, who became famous for his wonderful book on human evolution Your Inner Fish, has a fantastic new book out -- Some Assembly Required: Decoding Four Billion Years of Life, from Ancient Fossils to DNA.

Shubin's lucid prose makes for fascinating reading, as he takes you down the four-billion-year path from the first simple cells to the biodiversity of the modern Earth, wrapping in not only what we've discovered from the fossil record but the most recent innovations in DNA analysis that demonstrate our common ancestry with every other life form on the planet.  It's a wonderful survey of our current state of knowledge of evolutionary science, and will engage both scientist and layperson alike.  Get Shubin's latest -- and fasten your seatbelts for a wild ride through time.

All in the family

Over my nearly thirty years of teaching AP Biology, one of the topics that changed the most was taxonomy.

This might come as a surprise, given the changes in fields such as genetics, but honestly the two are closely related.  When I started my career, classification of species was done primarily by morphology (shape and structure), and the identification of which characteristics of an organism were plesiomorphies (structures inherited from, and therefore shared with, the ancestral species) and which were apomorphies (structures that were innovations unique to a single branch of the family tree).

One of many difficulties with this approach is that useful innovations can evolve more than once, and therefore aren't necessarily indicative of common ancestry.  This process, called convergent or parallel evolution, can generate some amazingly similar results, the most striking of which is the flying squirrel (a rodent) and the sugar glider (a marsupial), which look nearly identical at a quick glance (even a longer one, honestly).  To be fair, the fact that the two are not very closely related would be evident on any kind of moderately careful analysis, where giveaways like tooth structure and the presence of a pouch in the female sugar gliders would be enough to show they weren't on the same branch of the mammalian family tree.

Southern flying squirrel (top) [Image is in the Public Domain] and sugar glider (bottom) [Image licensed under the Creative Commons Joseph C Boone, Sugar Glider JCB, CC BY-SA 4.0]

But sometimes it's more difficult than that, and more than once taxonomists have created arrangements of the descent of groups of species only to find out that further study shows the original placement to be wrong.  As one of many examples, take the two groups of large-eyed nocturnal primates from southern and southeastern Asia, the lorises and tarsiers.  Based on habits and range, it's understandable that they were lumped together as "prosimians" on the same branch of the primate tree, but recent study has found the lorises are closely related to lemurs, and tarsiers are closer to monkeys and apes -- despite the superficial similarity.

Slow loris [Image licensed under the Creative Commons David Haring / Duke Lemur Center, Sublingua of a slow loris 001, CC BY-SA 3.0]

 

Tarsier [Image licensed under the Creative Commons yeowatzup, Tarsier Sanctuary, Corella, Bohol (2052878890), CC BY 2.0]

These revisions, and the sometimes surprising revelations they provide, have largely come from a change in how taxonomy is done.  Nearly all classification is now based upon genetics, not structure (although certainly structure plays a role in who we might initially hypothesize is related to whom).  But when it comes down to a fight between morphology and genetics, genetics always wins.  And this has forced us to change how we look at biological family trees -- especially when genetic evidence is obtained where it was previously absent.

This all comes up because of a discovery of intact DNA in a fossil of a primate much closer to us than the tarsiers and lorises -- a species from our own genus called Homo antecessor.  The species name suggests it was one of our direct ancestors, which is a little alarming because there's good evidence it was cannibalistic -- bones of the species found in Spain showed clear evidence of butchering for meat.

Now, however, the recovery of DNA from a tooth of an H. antecessor fossil -- at 800,000 years of age, the oldest DNA ever recovered from a hominid fossil -- has shown that it probably wasn't our ancestor after all, but a "sister clade," one that left no descendants.  (Bigfoot and the Yeti notwithstanding.)  The study was the subject of a paper in Nature last week, authored by a team led by Frido Welker of the University of Copenhagen, and required yet another reconfiguring of our own family tree.  The authors write:

The phylogenetic relationships between hominins of the Early Pleistocene epoch in Eurasia, such as Homo antecessor, and hominins that appear later in the fossil record during the Middle Pleistocene epoch, such as Homo sapiens, are highly debated.  For the oldest remains, the molecular study of these relationships is hindered by the degradation of ancient DNA.  However, recent research has demonstrated that the analysis of ancient proteins can address this challenge.  Here we present the dental enamel proteomes of H. antecessor from Atapuerca (Spain) and Homo erectus from Dmanisi (Georgia), two key fossil assemblages that have a central role in models of Pleistocene hominin morphology, dispersal and divergence.  We provide evidence that H. antecessor is a close sister lineage to subsequent Middle and Late Pleistocene hominins, including modern humans, Neanderthals and Denisovans.  This placement implies that the modern-like face of H. antecessor—that is, similar to that of modern humans—may have a considerably deep ancestry in the genus Homo, and that the cranial morphology of Neanderthals represents a derived form.

I find that last bit the most interesting, because it turns on its head our usual sense of being the Pinnacles of Evolution, clearly the most highly evolved (whatever the hell that actually means) species on the planet, definitely more advanced in all respects than those brute Neanderthals.  What this study suggests is that the flatter face of the Neanderthals is actually the apomorphy -- the more recently-evolved, "derived" characteristic -- and our narrower, more protruding faces are a plesiomorphy, inherited from our older ancestors.

This kind of stuff is why I'm endlessly interested in evolutionary biology -- as we find more data and develop new techniques, we refine our models, and in some cases have to overturn previously accepted conventional wisdom.  But that's what science is about, isn't it?  Basing your model on the best evidence you've got, and revising it if you get new and conflicting evidence.

 Just as well in this case.  One less cannibal in the family tree.  Not that there aren't probably others, but my genealogy already contains some sketchy enough characters.  No need to add more.

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This week's Skeptophilia book recommendation of the week is brand new -- only published three weeks ago.  Neil Shubin, who became famous for his wonderful book on human evolution Your Inner Fish, has a fantastic new book out -- Some Assembly Required: Decoding Four Billion Years of Life, from Ancient Fossils to DNA.

Shubin's lucid prose makes for fascinating reading, as he takes you down the four-billion-year path from the first simple cells to the biodiversity of the modern Earth, wrapping in not only what we've discovered from the fossil record but the most recent innovations in DNA analysis that demonstrate our common ancestry with every other life form on the planet.  It's a wonderful survey of our current state of knowledge of evolutionary science, and will engage both scientist and layperson alike.  Get Shubin's latest -- and fasten your seatbelts for a wild ride through time.

The planet detectors

Are you looking for something to occupy you while you're stuck home?  For the month of April, I'm putting my online course An Introduction to Critical Thinking on sale for $12.99 (it's ordinarily $49.99).  It includes an hour and a half of video lectures, some (fun) problem sets and readings, and you'll come away with a better ability to detect such things as hoaxes, pseudoscience, ripoffs, and fake news.  Use the coupon code STUCKATHOME4APR to get your discount!

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Long-time readers of Skeptophilia know I'm kind of obsessed with the idea of extraterrestrial life.  I guess it's natural enough; I'm a biologist who's also an amateur astronomer, and grew up on Lost in Space and Star Trek and The Invaders, and later The X Files and Star Wars.  (Although I'm aware this is kind of a chicken-and-egg situation, so what the ultimate origin of my obsession is, I'm not certain.)

Until fairly recently, there was no particularly good way to determine the likelihood of life on other worlds.  Decades ago astronomer Frank Drake came up with the famous Drake Equation, which uses the statistical principle that if you know the probabilities of various independent occurrences, to find the probability of all of them happening, you multiply them together.  Here's the Drake Equation:

[Image is in the Public Domain courtesy of NASA/JPL]

The problem, of course, is that the more uncertainty there is in the individual probabilities, the more uncertainty there is in the product.  And there was no way known to get even a close value -- or, worse, to know if the value you had reflected reality or was just a wild guess.

What's cool for us alien enthusiasts, though, is that our research and techniques have improved to the point where we do have decent estimates for the values of some of these.  Even better, every time one of them is revised, it's revised upward.  Today I'd like to look at two of them -- f(p) and n(e) -- respectively, the fraction of stars that have planetary systems, and the fraction of those systems that have at least one planet in the habitable zone.

Given that we started out with a sample size of one (1) solar system, no one knew whether the coalescence of stellar debris into planets was likely, or simply a lucky fluke.  Same for planets in the habitable zone; here we have only a single planet that is habitable for organisms like ourselves.  Again, is that some kind of happy accident, or would most planetary systems have at least one potentially habitable planet?

Once we started to find exoplanets, though, they seemed to be everywhere we looked.  The earliest ones were massive (probably Jupiter-like) planets, often in fast, close orbit, so they'd be pretty hostile places from our perspective.  (Although, as I dealt with in a recent post, what we're finding out about the resilience of life may mean we'll have to revise our definition of what constitutes the "habitable zone.")

So the estimates for f(p) and n(e) crept upward, but still, it was hard to get reliable numbers.  But just last week, two studies have suggested that f(p) -- the percentage of stars with multiple-planet systems -- may be very close to 100%.

In the first, we hear about a recently-developed technique to improve our ability to detect exoplanets even at great distances.  Before this, most exoplanets were discovered using one of two methods -- looking for stellar wobble as a planet and its star circle their mutual center of gravity (which only works for nearby stars with massive planets capable of generating a detectable wobble), and luminosity dips as a planet occludes (passes in front of) its host star (which only works if the orbital plane is lined up in such a way that the planet passes in front of the star as seen from Earth).  As you might imagine, those restrictions mean that we might well be missing most of the exoplanets out there.

Now, a new orbiting telescope developed by NASA -- called WFIRST (Wide Field Infrared Survey Telescope) -- has the capability to detect microlensing.  Microlensing occurs because of the warping of the fabric of space-time by massive objects.  As a planet rotates around its host star, that warp moves, creating a ripple -- and the light from any stars behind the planet gets deflected.  An analogy is when you're looking down to the bottom of a clear pond and a ripple on the surface passes you; the image of the pebbles on the bottom appears to waver.  That wavering of light from distant stars is what WFIRST is designed to detect.

The nice thing is that WFIRST isn't dependent on visible wobbles or planets with precisely-aligned orbital planes; it can see pretty much any planet out there with sufficient mass.  And it can detect them from much farther away than previous telescopes -- the Kepler Space Telescope could detect planets up to around a thousand light years away, while WFIRST extends that reach by a factor of ten.  It's also capable of scanning a great many more stars; the estimate is that the first sweep will look at two hundred million stars, which is a thousand times the number Kepler studied.

So chances are, we're going to see an exponential jump in the number of exoplanets we know of, and a corresponding uptick in the estimate for f(p).

The second study is much closer to home -- about as close as you can get without being in our own Solar System.  Proxima Centauri is the nearest star to us other than the Sun, at 4.244 light years away.  In 2016 we were all blown away by the announcement that not only did Proxima Centauri have a planet, it was (1) Earth-sized, and (2) in the habitable zone.  (Anyone want to board the Jupiter 2?)

Now, astronomers have discovered a second planet around Proxima, at a distance about 1.5 times the orbit of the Earth, and a mass of about twelve times Earth's.  This means it's probably something like Neptune, and very cold -- Proxima is a dim star, so the habitable zone is a lot closer to it than the Sun's is -- the estimate is that its average temperature is -200 C.

Even though it probably doesn't host life, it's exciting from the standpoint that Proxima's planetary system is looking more and more like ours.  As astronomer Phil Plait put it, over at his fantastic blog Bad Astronomy, "I hope this new planet candidate turns out to be real.  Having one planet orbiting the star is already pretty amazing, but having two?  In my mind that makes it a solar system.  And if two, why not more?  How about moons orbiting the planets, or asteroids and comets around the star, too?"

The impression I'm getting is that f(p) (the fraction of stars with planetary systems) and n(e) (the fraction of stars with at least one planet in the habitable zone) are both extremely high.  This bodes well for our search for life -- and as the techniques improve, my sense is that we'll find planets like ours pretty much everywhere we look.  So life is looking more and more likely to be plentiful out there.  Now, intelligent life that is sufficiently technological to communicate across interstellar space... that's another matter entirely.

But in my opinion, any time we can revise some part of the Drake Equation upward, it's a good thing.

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This week's Skeptophilia book recommendation of the week is brand new -- only published three weeks ago.  Neil Shubin, who became famous for his wonderful book on human evolution Your Inner Fish, has a fantastic new book out -- Some Assembly Required: Decoding Four Billion Years of Life, from Ancient Fossils to DNA.

Shubin's lucid prose makes for fascinating reading, as he takes you down the four-billion-year path from the first simple cells to the biodiversity of the modern Earth, wrapping in not only what we've discovered from the fossil record but the most recent innovations in DNA analysis that demonstrate our common ancestry with every other life form on the planet.  It's a wonderful survey of our current state of knowledge of evolutionary science, and will engage both scientist and layperson alike.  Get Shubin's latest -- and fasten your seatbelts for a wild ride through time.

Unicorn survival

One of the arguments you'll hear from cryptid enthusiasts is that the various critters they claim are real are survivals.  Nessie, Mokele-Mbémbé, and the Bunyip are modern-day brachiosaurs or plesiosaurs.  Bigfoot, the Fouke Monster, the Almas, the Florida Skunk Ape, and the Yowie are hominids, possibly australopithecenes.  The Beasts of Bodmin Moor and Exmoor, and the Mngwa of Tanzania, are related to prehistoric cats.  Mothman is supposed to be... okay, I don't know what the fuck Mothman is supposed to be.  Maybe descended from the rare saber-toothed butterfly, I dunno.

[Nota bene: if you're curious about any of these and want more information, check out the excellent cryptid list on Wikipedia, which has these and many others, along with lots of highly amusing illustrations thereof.]

The possibility of prehistoric survival is not without precedent.  The most famous is the coelacanth, one of the bizarre lobe-finned fish found in fossil form in sediments from before the Cretaceous Extinction, 66-odd million years ago.  They were allied to the lineage that led to amphibians (although that split took place a lot longer ago, so they weren't direct ancestors), and had lobe-like proto-limbs that give the group their name.  They were thought to be long extinct -- until a fisherman off the coast of Madagascar caught one in 1938.

Even that iconic mammal of prehistory, the woolly mammoth, survived a lot longer than most people thought.  The last remnant populations were thought to have been in northern North America and Siberia on the order of 25,000 years ago -- until fossils were found on Wrangell Island, off the coast of Alaska, dating to around 3,800 years ago, making them contemporaneous with the building of the Great Pyramids of Egypt.

So it's always risky to date a bunch of fossils and conclude that the most recent one marks the end of the species.  Not only is fossilization uncommon (something I've touched upon before), but there can be small remnant populations left in out-of-the-way places, and our inferences about when species became extinct can be off.

Sometimes by a lot.  Take, for example, Elasmotherium, which was the subject of a paper in The American Journal of Applied Sciences that a friend and loyal reader of Skeptophilia sent me last week.  Elasmotherium has sometimes been nicknamed "the Siberian Unicorn," which is a little misleading, because the only similarities between it and the typical graceful, fleet-footed concept of the unicorn is that it had one horn and four legs.  Here's an artist's rendition of Elasmotherium:

[Image is in the Public Domain, courtesy of artist Heinrich Harder]

If your thought is that it looks more like a rhinoceros than a one-horned horse, you're correct; the elasmotheres are cousins to the modern African rhinos.  What's interesting about them is that they were around during the Pleistocene, reaching their peak during the repeated glaciations, and were thought to have died out as the climate warmed, on the order of 350,000 years ago -- but this study found fossils from Kozhamzhar in Kazakhstan that dated to around 26,000 years ago.

"Most likely, the south of Western Siberia was a refugium, where this rhino persevered the longest in comparison with the rest of its range," said Andrey Shpanski, a paleontologist at Tomsk State University, who co-authored the paper.  "There is another possibility that it could migrate and dwell for a while in the more southern areas."

So it's a good bet that the elasmotheres -- like the woolly mammoth -- persisted a lot longer than paleontologists realized.

This is the main reason why, despite my general skepticism, I'm hesitant to discount reports of cryptids out of hand.  That most of them are either hoaxes or else misidentification of perfectly ordinary modern animals seems pretty likely, but "most" doesn't mean "all."  I'm very much in agreement on this count with what astronomer Michio Kaku said about UFOs: "Perhaps 98% of sightings can be dismissed as fabrications or as perfectly natural phenomena.  But that still leaves 2% that are unaccounted for, and to me, that 2% is well worth investigating."

So I'm all for continuing to consider claims of cryptids, as long as we evaluate them based upon the touchstone for all scientific research: hard evidence.  It's entirely possible some animals thought previously to be extinct have survived in remote areas, and have given rise to what we now call cryptozoology.  If that's the case, though, it should be accessible to the tools of science -- and, truthfully, just be zoology, no "crypto" about it.

Except for Mothman.  That mofo is scary.  I'd just as soon that one stays in the realm of legend, thank you very much.

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In the midst of a pandemic, it's easy to fall into one of two errors -- to lose focus on the other problems we're facing, and to decide it's all hopeless and give up.  Both are dangerous mistakes.  We have a great many issues to deal with besides stemming the spread and impact of COVID-19, but humanity will weather this and the other hurdles we have ahead.  This is no time for pessimism, much less nihilism.

That's one of the main gists in Yuval Noah Harari's recent book 21 Lessons for the 21st Century.  He takes a good hard look at some of our biggest concerns -- terrorism, climate change, privacy, homelessness/poverty, even the development of artificial intelligence and how that might impact our lives -- and while he's not such a Pollyanna that he proposes instant solutions for any of them, he looks at how each might be managed, both in terms of combatting the problem itself and changing our own posture toward it.

It's a fascinating book, and worth reading to brace us up against the naysayers who would have you believe it's all hopeless.  While I don't think anyone would call Harari's book a panacea, at least it's the start of a discussion we should be having at all levels, not only in our personal lives, but in the highest offices of government.