Who benefits?

There's an interesting idea from evolutionary theory called the cui bono principle.

Cui bono? is Latin for "who benefits?"  It started out as a legal concept; if a crime has been committed, and you're looking for the suspect, find out who benefitted.  That, very likely, will get you on the right path toward solving the mystery.

Cui bono in the evolutionary model has to do with explaining odd phenomena that seem to have no obvious underlying reason -- or which even induce organisms into self-destructive behavior.  One common example is the strange situation where certain ant species crawl up to the tops of blades of grass and basically just wait there to be eaten by herbivores.  It turns out that the bizarrely suicidal ants are infected with a parasite called a lancet worm that needs to complete its life cycle in the gut of a herbivorous mammal, so it damages the brain of the ant in just such a way as to turn its sense of direction upside down.  The parasitized ant then crawls upward instead of downward to safety, gets eaten -- and the lancet worm, of course, is the one who benefits.

Another, even creepier example, is Toxoplasma gondii, which I wrote about here at Skeptophilia a few years ago.  I encourage you to go back and read the post, but the upshot is this parasite -- which by some estimates infects half of the human population on Earth -- causes different symptoms in its three main hosts, cats, rats, and people.  Each set of symptoms is tailored to change behavior in very specific ways, with one end in mind; allowing the parasite to jump to its next host.

I just found out about another very peculiar (and convoluted) example of cui bono just yesterday, this one involving rice plants.  Many plants, it turns out, have pheromonal signaling, releasing chemicals into the air that then trigger responses in neighboring individuals, either of their own or of different species.  Acacia trees that are browsed by herbivores, for example, emit a signal that triggers nearby trees to produce bitter tannins, discouraging further snacking on the leaves.  Well, it turns out that rice plants have an even niftier strategy; attacked by insect pests, the rice plants emit a chemical called methyl salicylate (better known as oil of wintergreen), which attracts parasitoids -- insects like chalcid wasps that attack and kill the offending pests, usually by laying an egg in or on them and allowing the larvae to eat the pests for lunch.

Okay, but this has yet another layer of complexity, because there's a different set of organisms that have another take on cui bono.  Rice are subject to a group of plant viruses called tenuiviruses, which cause rice stripe disease, weakening or killing plants and severely reducing crop yield.  Tenuiviruses are spread by insect pests like planthoppers, which (much like mosquitoes with malaria, dengue fever, yellow fever, and chikungunya) suck up the sap of infected plants and the virus along with it, move on to an uninfected host, and spread the disease.

Rice stripe tenuivirus [Image credit: A. M. Espinoza]

And new research has found that the tenuiviruses, once in an infected plant's tissues, suppress the plant's ability to produce methyl salicylate.  The result?  The plant can't send a signal to the parasitoids, the planthoppers multiply, and the disease spreads.

The authors write:

[R]ice viruses inhibit methyl salicylate (MeSA) emission, impairing parasitoid recruitment and promoting vector persistence.  Field experiments demonstrate that MeSA, a key herbivore-induced volatile, suppresses vector populations by attracting egg parasitoids.  Viruses counter this by targeting basic-helix-loop-helix transcription factor OsMYC2, a jasmonic acid signaling hub, thereby down-regulating OsBSMT1 and MeSA biosynthesis, responses conserved across diverse rice viruses and vector species.

So once again, we have a parasitic microorganism that is engineering a response in its host that makes it more likely to be passed on, in this case by preventing the host from calling for help.

This kind of strategy brings Tennyson's observation that "nature is red in tooth and claw" to new heights, doesn't it?  Makes you wonder how many other examples there are out there of behavior being manipulated by parasites.  Further evidence that evolution is the Law of Whatever Works -- even if Whatever Works is kind of unsettling.

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The advantage of simplicity

One of the most common misconceptions about evolution is that it is goal-oriented.

You hear it all the time.  Giraffes evolved longer necks so they could reach foliage higher up in tree branches -- as if some poor short-necked giraffes  were trundling about on the African savanna looking longingly up into the canopy and thinking, "Wow, that looks amazing," so their kids were born with longer necks.  It becomes even more insidious when you start talking about human evolution, because the way it's often presented is that waaaaaay back you had something like a jellyfish that evolved into something like a worm, and then into a primitive fish, into an amphibian, into a reptile, into a proto-mammal, into true mammals then primates then...

... us.  Sitting, of course, on the very top as befits the pinnacle of evolution, as if all along we're what the whole process had been aiming at.

This misses the boat in several very important ways.  One is that this linear view of evolution is simply wrong.  Evolution causes repeated branching; in fact, in our own lineage, many of the basic body plans we have today (flatworms, roundworms, jellyfish, annelids, mollusks, echinoderms, arthropods, and primitive vertebrates) all arose at around the same time, during what's called the Cambrian explosion.  During the intervening 540-million-odd years since that happened, some of the branches of the tree of life have changed a great deal more than others; but all living things on Earth have exactly the same length of evolutionary history.

A really critical way that the teleological model for evolution fails is that it misses completely how evolution actually works.  Natural selection isn't forward-looking at all; it operates by the environment selecting the forms that have the highest survival and reproductive potential now, irrespective of what the conditions might be a week from Tuesday.  It is very much the Law of Whatever Works, and what works today might not work at all if conditions change -- something we should pay attention to apropos of climate change.

A third problem is the perception that evolution always leads to higher complexity, strength, and intelligence.  None of these are true.  Consider that insects, especially beetles, are the most numerous and diverse animals on Earth by far -- both species-wise, and individual-for-individual, insects outnumber all other animals put together.  Sometimes simplicity has a higher survival advantage than complexity does, and -- to judge by the natural world, and even a significant fraction of the human part of it -- I'm not convinced that intelligence is always an advantage, either.

As a good example of the advantage of simplicity -- and the reason the topic comes up today -- consider the little plant species Balanophora fungosa.  It's found in warm, moist forests in Taiwan, Japan, and Okinawa, and on first glance it looks like a strange mushroom.  Balanophora is in the family Balanophoraceae, which comprises sixteen genera and is somewhat tentatively placed in order Santalales along with more familiar plants like sandalwood and mistletoe.  All the members of Balanophoraceae are obligate parasites, living off the roots of very specific species of trees.

Balanophora fungosa [Image credit: Petra Svetlikova]

Where it gets interesting is that Balanophora has done what superficially looks like evolution in reverse.  It's lost its ability to produce chlorophyll; it has no conventional root system.  Most of the plant kingdom have on the order of two hundred genes whose job it is to produce and operate plastids, the pigment-containing organelles that include chloroplasts; Balanophora has reduced that number to twenty.  Many species in Balanophoraceae produce seeds without fertilization, obviating the need for flowers.

What's curious is that these odd little plants have been around for a long time.  They branched off from the rest of the plant kingdom in the mid-Cretaceous period, something like a hundred million years ago, and have been quietly doing their thing ever since, gradually evolving to jettison structures (and even genes) they don't need along the way.  "Balanophora has lost much of what defines it as a plant, but retained enough to function as a parasite," said Petra Svetlikova, of the Okinawa Institute of Science and Technology, who led the study.  "It's a fascinating example of how something so strange can evolve from an ancestor that looked like a normal plant with leaves and a normal root system."

Because of its extreme specialization, both in terms of habitat and host species, Balanophora is threatened by habitat change.  "Most known habitats of Balanophora are protected in Okinawa, but the populations face extinction by logging and unauthorized collection," Svetlikova said.  "We hope to learn as much as we can about this fantastic, ancient plant before it's too late.  It serves as a reminder of how evolution continues to surprise us."

So there you have some cool research about an evolutionary holdout from a hundred-million-year-old split in the tree of life.  Here, simplicity, not complexity, seems to have been the key to its long survival.  One can only hope that this strange little plant hasn't lasted so long only to reach the end because of us.

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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've gone on and on in previous posts 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, 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 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 one hundred percent 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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Resurrection

The environmentalists tell us "extinction is forever," and that certainly seems unarguable.  Once a species is lost, evolution will never recreate it.  You may get something that looks like it; there are numerous examples of Elvis taxa, species that evolved to fit vacated niches and underwent convergent evolution resulting in a similarity to some extinct form.  (The name comes from the huge numbers of Elvis impersonators that have popped up since the original's death in 1977.)  But the sad truth is that the original is gone forever.

The issue, though, can be making certain the species actually is extinct.  There are ongoing efforts to find relic populations of a number of presumed-extinct species (two of the best known are the ivory-billed woodpecker and the thylacine).  Naysayers have criticized the efforts to find these species as nothing more than wishful thinking, but it bears keeping in mind that there is a long list of organisms thought to be extinct that have turned out to be very much alive.

They're called Lazarus taxa, after the biblical character Jesus raised from the dead.  Some of them are astonishing.  The one that always comes to mind for most people is the coelacanth, a crossopterygian fish that was only known from fossils preceding the Cretaceous Extinction sixty-six million years ago, which was discovered living in the Indian Ocean in 1938.  But that's only one of many.  Here's a sampler of Lazarus taxa:

• The South American bush dog (now split into three separate species in the genus Speothos) was only known from some Pleistocene-age bones found in a Brazilian cave, but is now known to have a range from southern Central America all the way to northern Paraguay.  Its reclusive habits and rarity still make it the least-studied canid in the world.

A Brazilian bush dog [Image licensed under the Creative Commons Xerini, Waldhund, CC BY-SA 3.0]

• The nightcap oak (Eidothea hardeniana and E. zoexylocarya), which aren't oaks at all but a member of the Protea family (Proteaceae), were known only from fifteen-million-year-old fossils -- and then a stand of them were discovered growing in a remote part of Australia.  The Royal Botanical Gardens in Sydney has a cultivation program for the two species, which are threatened because the seeds are frequently eaten by introduced mice.

Eidothea hardeniana [Image is in the Public Domain]

• The monito del monte, or colocolo opossum (Dromiciops gliroides), was not only thought to have gone extinct eleven million years ago, it was believed that its entire order (Microbiotheria) was gone as well.  It was found -- alive -- in the temperate bamboo forests of the southern Andes Mountains in 1894, and has no near relatives anywhere in the world.  (The closest are the Australian marsupials, but even those are very distant cousins.)

[Image licensed under the Creative Commons José Luis Bartheld from Valdivia, Chile, Monito del Monte ps6, CC BY 2.0]

• In 1898 a fish was discovered that was a near perfect match to Oligocene-age fossils on the order of twenty-eight million years old.  It's Lignobrycon myersi, and is only known from the Rio Braço and Rio Contas in east-central Brazil.  Somehow, it alone of its genus survived through all of those years and made it down to the present day.

[Image licensed under the Creative Commons Alexandre dos Santos Rodrigues et. al., Lignobrycon myersi specimens (9382613) (cropped), CC BY 4.0]

• The monoplacophorans were a group of mollusks common during the Silurian and Devonian Periods, but were last seen in the fossil record in the mid- to late-Devonian, around 375 million years ago.  After that -- nothing.  Reasonably, biologists thought they'd gone extinct, until live monoplacophorans were discovered in deep water off the west coast of Costa Rica.  Further surveys have found no fewer than thirty-seven different species in deep water across the Pacific.

A live specimen of Neopilina filmed off the coast of Samoa by the 2017 Okeanos Explorer mission [Image is in the Public Domain courtesy of NOAA]

• Even the monoplacophorans don't hold the survival record, though.  That honor goes to Rhabdopleura, which is a graptolite -- a (very) distant relative of chordates known mainly through Cambrian-age fossils.  The last Rhabodopleura was thought to have gone extinct in the mid-Cambrian, five hundred million years ago (and the rest of the group didn't make it past the mid-Carboniferous).  In 1869 they were discovered living in the deep water of the Pacific, and since that time nine living species have been identified.

A drawing of Rhabdopleura normani [Image is in the Public Domain]

While the general rule still applies -- extinction is forever -- it's worth keeping in mind that sometimes we find ourselves in a situation a little like Mark Twain did, resulting in his quip, "Rumors of my death were great exaggerations."  The Earth is a big place, and there are still plenty of poorly-explored regions where we might well have lots of surprises in store.

All of which should be encouraging to the folks out there chasing the ivory-billed woodpecker and thylacine.  Don't give up hope.  If Rhabdopleura could survive for five hundred million years unobserved, surely these two could manage a century or so.

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Birdwalking into the Miocene

From the One Thing Leads To Another department, we have: a cute little fuzzy mammal from Madagascar, some thoughts about genetic drift, and a period of geological history during which a lot was happening.

I'd like to say that this kind of twisty mental path is infrequent for me, but unfortunately, it happens pretty much on a daily basis, and has since I was a kid.  When I was around twelve years old, my parents splurged on a set of Encyclopedia Brittanica, ostensibly to assist me with my schoolwork, but they (the Encyclopedia, not my parents) were honestly more of a hindrance than a help.  I'd go to the Brittanica to look up, say, something about the Monroe Doctrine for social studies class, and my mom would find me three hours later with fifteen open volumes spread on the floor around me, with me in the middle immersed in an article about venomous snakes in Malaysia.

It's why conversations with my older son, with whom I seem to share a brain, are like some kind of weird exercise in free association.  We've occasionally tried to reconstruct the pathway by which we got to a particular topic, and there's usually a logical connection between each step and the preceding one, but overall, our discussions give new meaning to the word labyrinthine.

Anyhow, today I started on this particular birdwalk when someone posted a photograph on social media of an animal I'd never heard of: the ring-tailed vontsira (Galidia elegans).  The vontsira is kind of adorable:

[Image licensed under the Creative Commons Charles J. Sharp creator QS:P170,Q54800218, Ring-tailed vontsira (Galidia elegans) 2, CC BY-SA 4.0]

The vontsira and its relative the falanouc are in the family Eupleridae along with a species I had heard of, the fossa, which is a sleek, elegant, weasel-like animal that is only distantly related to other members of the Order Carnivora.  All of the eupleurids live in Madagascar, and like most of the endemic species on the island, they're threatened by habitat loss and competition from non-native species.

What I found most curious about these mammals is that they're a clade -- genetic studies have found that eupleurids all descend from a single small population that arrived in Madagascar something like twenty million years ago, and then diversified into the species you see today.  Chances are, the ancestors of the vontsira, falanouc, fossa, and other eupleurids came over from Africa via rafting in the early Miocene Epoch.  They're distant cousins of the much more common and widespread mongooses, hyaenas, genets, and civets, and it was probably some prehistoric viverroid (the parvorder that includes all five groups) that made its way to Madagascar and gave rise to modern eupleurids.

This led me to looking into what was happening, geology-wise, during the Miocene.  I knew it was a busy time, but I didn't realize just how busy.  Tectonic movement closed off the Mediterranean Sea from the Indian Ocean, and then a shift at the western end of the Mediterranean closed off the Straits of Gibraltar; the result was that the Mediterranean dried up almost completely, something called the Messinian salinity crisis because what was left was a salty desert with an average temperature of something like 110 F and two disconnected lakes of concentrated brine.  At the end of the epoch, another plate movement reopened the Straits, and there was a flood of a magnitude that beggars belief; at its peak, the flow rate was enough to raise the level of the refilling Mediterranean by ten meters per day.

This is also the period during which the Indian subcontinent rammed into Asia, raising the Himalayas and introducing a bunch of African species into Asia (this is why there are lemurs in Madagascar and India, but none in the Middle East).  Also, it's when the Columbia River Flood Basalts formed -- an enormous (175,00 cubic kilometers) blob of igneous rock covering what is now eastern Washington and Oregon, and the west parts of Idaho -- an eruption probably due to the same hotspot which now underlies Yellowstone.

Because of all this, the climate during the Miocene might as well have been attached to a yo-yo.  Warm periods rapidly alternated with cold ones, and wet with dry.  As you might imagine, this played hell with species' ability to adapt, and groups came and went as the epoch passed -- the borophagine ("bone-crushing") canids, the terrifying "hypercarnivorous" hyaenodonts, and the enormous, superficially pig-like entelodonts amongst them.  The first apes evolved, and the split between the ancestors of modern humans and modern chimps occurred in the late Miocene, something like seven million years ago.

If all that wasn't enough, some time during the Miocene -- geologists are uncertain exactly when -- there was an asteroid impact in what is now Tajikistan, forming the twenty-five-kilometer-wide Karakul Crater Lake, which at an elevation of 3,960 meters is higher than the much better-known Lake Titicaca.

So there you have it.  A brief tour of the chaotic paths through my brain, starting with a furry woodland animal from Madagascar and ending with a meteorite impact in Tajikistan.  Hopefully you found some stops along the way interesting.  Now y'all'll have to excuse me, because I need to go look up a single fact in Wikipedia to answer a question a friend asked about linguistics.  You'll find me in a few hours reading about how general relativity applies to supermassive black holes.

I'm sure how I got there will make sense to me, at least.

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Life, complexity, and evolution

Next to the purely religious arguments -- those that boil down to "it's in the Bible, so I believe it" -- the most common objection I hear to the evolutionary model is that "you can't get order out of chaos."

Or -- which amounts to the same thing -- "you can't get complexity from simplicity."  Usually followed up by the Intelligent Design argument that if you saw the parts from which an airplane is built, and then saw an intact airplane, you would know there had to be a builder who put the parts together.  This is unfortunately often coupled with some argument about how the Second Law of Thermodynamics (one formulation of which is, "in a closed system, the total entropy always increases") prohibits biological evolution, which shows a lack of understanding both of evolution and thermodynamics.  For one thing, the biosphere is very much not a closed system; it has a constant flow of energy through it (mostly from the Sun).  Turn that energy source off, and our entropy would increase post-haste.  Also, the decrease in entropy you see within the system, such as the development of an organism from a single fertilized egg cell, does increase the entropy as a whole.  In fact, the entropy increase from the breakdown of the food molecules required for an organism to grow is greater than the entropy decrease within the developing organism itself.

Just as the Second Law predicts.

So the thermodynamic argument doesn't work.  But the whole question of how you get complexity in the first place is not so easily answered.  On its surface, it seems like a valid objection.  How could we start out with a broth of raw materials -- the "primordial soup" -- and even with a suitable energy source, have them self-organize into complex living cells?

Well, it turns out it's possible.  All it takes -- on the molecular, cellular, or organismal level -- is (1) a rule for replication, and (2) a rule for selection.  For example, with DNA, it can replicate itself, and the replication process is accurate but not flawless; the selection process comes in with the fact that some of those varying DNA configurations are better than others at copying themselves, so those survive and the less successful ones don't.  From those two simple rules, things can get complex fast.

But to take a non-biological example that is also kind of mindblowing, have you heard of British mathematician John Horton Conway's "Game of Life?"

In the 1960s Conway became interested in a mathematical concept called a cellular automaton.  The gist, first proposed by Hungarian mathematician John von Neumann, is to look at arrays of "cells" that then can interact with each other by a discrete set of rules, and see how their behavior evolves.  The set-up can get as fancy as you like, but Conway decided to keep it really simple, and came up with the ground rules for what is now called his "Game of Life."  You start out with a grid of squares, where each square touches (either on a side or a corner) eight neighboring cells.  Each square can be filled ("alive") or empty ("dead").  You then input a starting pattern -- analogous to the raw materials in the primordial soup -- and turn it loose.  After that, four rules determine how the pattern evolves:

1. Any live cell that has fewer than two live neighbors dies.
2. Any live cell that has two or three live neighbors lives to the next round.
3. Any live cell that has four or more live neighbors dies.
4. Any dead cell that has exactly three live neighbors becomes a live cell.

Seems pretty simple, doesn't it?  It turns out that the behavior of patterns in the Game of Life is so wildly complex that it's kept mathematicians busy for decades.  Here's one example, called "Gosper's Glider Gun":

Some start with as few as five live cells, and give rise to amazingly complicated results.  Others have been found that do some awfully strange stuff, like this one, called the "Puffer Breeder":

What's astonishing is not only how complex this gets, but how unpredictable it is.  One of the most curious results that has come from studying the Game of Life is that some starting conditions lead to what appears to be chaos; in other cases, the chaos settles down after hundreds, or thousands, of rounds, eventually falling into a stable pattern (either one that oscillates between two or three states, or produces something regular like the Glider Gun).  Sometimes, however, the chaos seems to be permanent -- although because there's no way to carry the process to infinity, you can't really be certain.  There also appears to be no way to predict from the initial state where it will end up ahead of time; no algorithm exists to take the input and determine what the eventual output will be.  You just have to run the program and see what happens.

In fact, the Game of Life is often used as an example of Turing's Halting Problem -- that in general there is no way to be certain that a given algorithm will arrive at a solution in a finite number of steps.  This theorem arises from such mind-bending weirdness as the Gödel Incompleteness Theorem, which proved rigorously that within mathematics, there are true statements that cannot be proven and false statements that cannot be disproven.  (Yes -- it's a proof of unprovability.)

All of this, from a two-dimensional grid of squares and four rules so simple a fourth-grader could understand them.

Now, this is not meant to imply that biological systems work the same way as an algorithmic mathematical system; just a couple of weeks ago, I did an entire post about the dangers of treating an analogy as reality.  My point here is that there is no truth to the claim that complexity can't arise spontaneously from simplicity.  Given a source of energy, and some rules to govern how the system can evolve, you can end up with astonishing complexity in a relatively short amount of time.

People studying the Game of Life have come up with twists on it to make it even more complicated, because why stick with two dimensions and squares?  There are ones with hexagonal grids (which requires a slightly different set of rules), ones on spheres, and this lovely example of a pattern evolving on a toroidal trefoil knot:

Kind of mesmerizing, isn't it?

The universe is a strange and complex place, and we need to be careful before we make pronouncements like "That couldn't happen."  Often these are just subtle reconfigurations of the Argument from Ignorance -- "I don't understand how that could happen, therefore it must be impossible."  The natural world has a way of taking our understanding and turning it on its head, which is why science will never end.  As astrophysicist Neil deGrasse Tyson explained, "Surrounding the sea of our knowledge is a boundary that I call the Perimeter of Ignorance.  As we push outward, and explain more and more, it doesn't erase the Perimeter of Ignorance; all it does is make it bigger.  In science, every question we answer raises more questions.  As a scientist, you have to become comfortable with not knowing.  We're always 'back at the drawing board.'  If you're not, you're not doing science."

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Creepy crawlies

Whenever we have a wet summer -- not an uncommon occurrence in our rainy climate -- we have a plague of little pests trying to get into our house.

They're called millipedes, slinky guys maybe a couple of centimeters long, with lots of legs (not a thousand, though).  They're completely harmless; they don't bite like their cousins the centipedes do, and if you poke at them, they coil up into a ball.  So I guess they're really more of a nuisance than an actual problem.  They don't even damage anything, the way mice can.  Mostly what they seem to do is get in through every crack and crevice (there are lots of these in a big old house like ours), look around for a while, then curl up and die.

[Image licensed under the Creative Commons Totodu74, Anadenobolus monilicornis 03, CC BY-SA 3.0]

So I don't like them, and I wish they stayed outside, but in the grand scheme of things they're no big deal.  Imagine, though, if they were bigger.

A lot bigger.

Recently, paleontologists announced the discovery on a beach in Northumberland, England, of a millipede fossil from the Carboniferous Period.  It's been dated to the middle of the period, about 326 million years ago.  It looks a bit like the millipedes I see trundling across my basement floor in summer.

Only this one was 2.6 meters long (approximately the length of a Mini Cooper), a half a meter across, and weighed something on the order of fifty kilograms.

It's been named Arthropleura, and holds the record as the largest-known arthropod in Earth's history.  Nothing is known for sure about its behavior; if it's like the rest of millipedes, it was a scavenger on leaf detritus, but there's no way to know for certain.  Given its size, it could well have been a lot more dangerous than the ones we have around now.  To paraphrase the old joke about five-hundred-pound gorillas:

Q: What does a fifty-kilogram millipede eat?

A: Anything it wants.

Those of you who are (like me) biology nerds may be frowning in puzzlement at this point.  How on earth could an arthropod get so big?  Their size is limited by the inefficiency of their respiratory system (not to mention the weight of their exoskeletons).  Most arthropods (millipedes included) breathe through pairs of holes called spiracles along the sides of the body.  These holes open into a network of channels called tracheae, which bring oxygen directly to the tissues.  Contrast that with our system; we have a central oxygen-collecting device (lungs), and the hemoglobin in our blood acts as a carrier to bring that oxygen to the tissues.  It's a lot more efficient, which is why the largest mammals are a great deal bigger than the largest arthropods.  (So, no worries that the bad sci-fi movies from the 50s and 60s, with giant cockroaches attacking Detroit, could actually happen.  A ten-meter-long cockroach not only wouldn't be able to oxygenate its own tissues fast enough to survive, it couldn't support its own weight.  It wouldn't eat Detroit, it would just lie there and quietly suffocate.)

So how could there be such ridiculously enormous millipedes?

The answer is as fascinating as the beast itself is.  As the temperature warmed and rainfall increased after the previous period (the Devonian), it facilitated the growth of huge swaths of rain forest across the globe.  In fact, it's the plant material from these rain forests that produced the coal seams that give the Carboniferous its name.  But the photosynthesis of all these plants drove the oxygen levels up -- by some estimates, to around 35% (contrast that to the atmosphere's current 21% oxygen).  This higher oxygen level facilitated the growth of animals who are limited by their ability to uptake it -- i.e., arthropods. (At the same time, there was a dragonfly species called Meganeura with a seventy-centimeter wingspan.  And unlike millipedes, these things were carnivores, just as modern dragonflies are.)

Eventually, though, the system was unsustainable, and a lot of the rain forests began to die off in the Late Carboniferous, leading to a drier, cooler climate.  However, remember the coal seams -- by that time a huge percentage of the carbon dioxide that had fed the photosynthesis of those rain forests was now locked underground.  The fuse was lit for a catastrophe.

Fast forward to the end of the next period, the Permian, 255 million years ago.  What seems to have happened is a series of colossal volcanic eruptions that created the Siberian Traps, a basalt deposit covering most of what is now Siberia.  The lava ripped through the coal seams, blasting all that stored carbon into the atmosphere as carbon dioxide.  The temperature in the late Permian had been cool and dry, and the spike of carbon dioxide created a commensurate spike in the temperature -- as well as a huge drop in oxygen, used up by the burning coal.  The oxygen concentration seems to have bottomed out at around twelve percent, just over half of what it is now.  The extra carbon dioxide dissolved into ocean water, dropping the pH, and the increasing acidity dissolved away the shells of animals who build them out of calcium carbonate -- e.g. corals and mollusks.

Wide swaths of ocean became anoxic, acidic dead zones.  The anaerobic organisms began to eat through all the dead organic matter, churning out more carbon dioxide and another nasty waste product, sulfur dioxide (which gives the horrible smell to rotten eggs, and is also an acidifier).  The result: an extinction that wiped out an estimated ninety percent of life on Earth. In short order, a thriving planet had been turned into a hot, dead, foul-smelling wasteland, and it would take millions of years to recover even a fraction of the previous biodiversity.

Of course, at highest risk would be the big guys like our friends Arthropleura and Meganeura, and the Earth hasn't seen giant arthropods like this since then.  Today, the largest arthropod known is the Japanese spider crab (Macrocheira), topping out at around twenty kilograms -- but crabs and other crustaceans have gills and an oxygen carrier called hemocyanin, so they can boost the efficiency of their respiratory system somewhat over their terrestrial cousins.  The largest insect today is the African Goliath beetle (Goliathus), at about a tenth of a kilogram.  And in today's atmosphere, it's at a pretty significant disadvantage.  They may look big and scary, but in reality, they're slow-moving, harmless creatures.  Kind of a beer can with six legs, is how I think of them.

So that's today's look at creepy-crawlies of the past.  In my opinion it's just as well the big ones became extinct. The last thing I need is having to shoo a fifty-kilogram millipede out of my basement.

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Life converges

One of the most fascinating features of biological evolution -- particularly as it applies to the possibility of life on other planets -- has to do with the concept of constraint.

Which features of life on Earth are, in some sense, inevitable?  Are there characteristics of terrestrial organisms that we might expect to find on any inhabitable world?  Stephen Jay Gould looked at this question in his essay "Replaying the Tape," from his brilliant book on the Cambrian Explosion, Wonderful Life:

You press the rewind button and, making sure you thoroughly erase everything that actually happened, go back to any time and place in the past -– say, to the seas of the Burgess Shale.  Then let the tape run again and see if the repetition looks at all like the original.  If each replay strongly resembles life’s actual pathway, then we must conclude that what really happened pretty much had to occur.  But suppose that the experimental versions all yield sensible results strikingly different from the actual history of life?  What could we then say about the predictability of self-conscious intelligence?  or of mammals?

Some features that have been suggested as evolutionarily constrained, with arguments of varying levels of persuasiveness, are:

• a genetic code based on some kind of nucleic acid (DNA or RNA, or some chemical analogue)
• internal cell membranes made of phospholipids, to segregate competing chemical reactions from each other 
• multicellularity, with some level of tissue specialization
• in more complex organisms, some form of symmetry, with symmetrically-placed organs
• some kind of rapid-transit system for messages, analogous to our nervous system (but perhaps not structured the same way)
• cephalization -- concentration of the central processing centers and sensory organs near the head end

It's interesting when science fiction tackles this issue -- and sometimes comes up with possible pathways for evolution that don't result in humanoids with strangely-shaped ears and odd facial protuberances.  A few that come to mind are Star Trek's silicon-based Horta from the episode"Devil in the Dark," the blood-drinking fog creature from "Obsession," the giant single-celled neural parasites from "Operation Annihilate," and Doctor Who's Vashta Nerada, Not-Things, Gelth, and Midnight Entity.

So the search for extraterrestrial life requires we consider looking not only for "life as we know it, Jim," but life as we don't know it.  Or, more accurately, to consider to what extent our terrestrial biases might be blinding us to the possibility of what evolution could create.

It's worth considering, however, how often evolution here on Earth ends up landing on the same solutions to the problems of survival and reproduction over and over again, a phenomenon called convergent evolution.  Eyes, or analogous light receptor organs, have evolved multiple times -- some biologists have suggested as many as fifty different independent lineages that evolved some form of eye.  Wings occurred separately in four groups of animals -- birds, pterosaurs, insects, and bats.  (If you include structures for gliding, add flying squirrels, sugar gliders, colugos, flying fish, and flying lizards.)

Even biochemical pathways can reappear, something I find astonishing.  Take, for example, the research that came out this week in Nature Chemical Biology, which found that two only distantly-related plants -- ipecac (Carapichea ipecacuanha), in the gentian family, and sage-leaved alangium (Alangium salviifolium), in the dogwood family, have both come up with complex biochemical pathways to generate the same set of bitter, emetic compounds -- ipecacuanha alkaloids.

The last common ancestor of these two species was over a hundred million years ago, so there's a strong argument that they evolved this capacity independently.  And indeed, when the biochemists looked at the enzymatic pathways, they're different -- they found entirely different chemical synthesis methods for producing the same set of end products.  Weirdest of all, they both evolved an enzyme that cleaves a sugar molecule from the alkaloid precursor, and that's what activates it (i.e., makes it toxic).  In the living plant's tissues, the enzyme and the precursor are segregated from each other.  It's only when they're brought together -- such as when a herbivore chomps on the leaves -- that the sugar is split away from the precursor, the alkaloid is activated, and the herbivore starts puking its guts up.

Clever strategy.  So clever, in fact, that it was stumbled upon by two entirely separate lineages of plants.  The rules organisms play by are the same, so perhaps not surprising there are similar outcomes sometimes.

The whole thing highlights the fact that there is a limited range of solutions for the fundamental difficulties of existence.  It has to make you wonder if, when we do find life elsewhere in the universe, it might look a lot more familiar that we're expecting.  I don't think it's likely we'll bump into Romulans or Ice Warriors or Krillitane, but maybe there are features of life on Earth that will re-evolve in just about any conceivable habitable planet.

But hopefully there won't be any Vashta Nerada.  Those things are terrifying.

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The most alien-looking place on Earth

George Wynn Brereton Huntingford was a British anthropologist, linguist, and historian, who traveled widely and was famed for his perceptive observations of societies and cultures.  And if you had to guess which of the many places he traveled during his 77 year life he labeled "the most alien-looking place on Earth," what would you come up with?

His vote was for the island of Socotra, a 132-by-42 kilometer island which lies at at the mouth of the Gulf of Aden.  To the north is the Arabian Sea; to the southwest, the Guardafui Channel separates it from the Horn of Africa.  It's nearer to Africa than to the Arabian Peninsula (232 versus 380 kilometers), but is controlled by the government of Yemen, as much as Yemen's political disaster is currently controlling anything.

Most of Socotra is desert to semi-desert:

[Image licensed under the Creative Commons Rod Waddington from Kergunyah, Australia, Socotra Island (11007223546), CC BY-SA 2.0]

Although it does get more rainfall than either Yemen and Oman (to the north) or Somalia (to the east), so it has a great deal more vegetation than its neighbors:

[Image licensed under the Creative Commons Rod Waddington from Kergunyah, Australia, Wadi, Socotra Island (14495206039), CC BY-SA 2.0]

The main reason for Socotra's uniqueness -- and why evolutionary biologist Lisa Banfield called it "the Galapagos of the Indian Ocean" -- isn't the climate; it's the fact that geologically, it's part of Africa.  During the Miocene Period, about twenty million years ago, Africa and the Arabian Peninsula were joined, but a rift formed that split the two, opening up the Gulf of Aden.  Socotra is a chunk of the Somali Plate that was torn loose and got separated from the rest of the land mass that now forms the easternmost part of Africa.  (Interestingly, the rifting has continued, joining up with a fault system that runs up north through the Red Sea and south into the East African Rift Zone, which one day will tear away a much huger chunk of Africa -- all the way down to Mozambique.)

The issue is that since Socotra's separation from Africa around twenty million years ago, it's been largely isolated, so evolution has veered the community off into its own direction..  This has led to a high degree of endemism -- the fraction of species found nowhere else on Earth.  11% of its bird species, 37% of its plants, 90% of its reptiles, and 95% of its mollusk species are endemic.  One of the most iconic plants is the "dragon's blood tree" (Dracaena cinnabari), which looks like it was invented by Dr. Seuss:

[Image licensed under the Creative Commons Alex38, Dragonblood tree in Socotra 2, CC BY 4.0]

Then, there's the cucumber tree (Dendrosicyos socotranus), which -- as the name would suggest -- is the only species in the cucumber family (Cucurbitaceae) that grows into a tree.  As far as I've heard, though, the fruit isn't edible, which is a good thing, because it'd be a hell of a climb to harvest one for your dinner salad:

[Image licensed under the Creative Commons Gerry & Bonni, Cucumber tree (6407165121), CC BY 2.0]

Like many places with unique and isolated ecosystems, Socotra's oddball assemblage of biota are endangered, from introduced species like cats and rats, from land use by the island's sixty-thousand-odd inhabitants, and from climate change.  The ongoing Yemeni civil war isn't helping, either; the government's priority is certainly not protecting peculiar-looking trees, and the ecotourists whose revenue might help the situation are mostly staying away for their own safety.

In any case, that's one anthropologist's vote for "the most alien-looking place on Earth" -- an island that's geologically African, politically and culturally Arabian, and biologically like nowhere else.  It's a place I'd love to visit one day if the situation calms down.  Adding some bird species to my life list that are found only on one speck of land in the Arabian Sea would be amazing.

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