Picky eaters

Last week a gardener friend and I were talking about the fact that some plants are extreme specialists -- they only thrive in a very narrow range of conditions.

The classic example of this are orchids.  Virtually all orchid species only do well if you can somehow replicate the exact conditions of temperature, soil pH, soil mineral content, sunlight, and so on that they need.  Some also require the presence of symbiotic fungi (such as mycorrhizae) that infiltrate the orchid's roots and aid in nutrient and water uptake.  All of this is why if you ever are lucky enough to see an orchid growing in the wild, resist the temptation of digging it up and bringing it home for your garden.  The chances are nearly one hundred percent that all you'll succeed in doing is killing it in short order.  (Also, if you live in a place with laws against harming endangered species, you might be looking at serious fines if you get caught.)

It's an interesting question to consider why such extreme specialization evolves.  On first glance, it seems like it'd be better for all species to evolve toward becoming generalists -- able to handle a wide range of conditions.  The thing is that while generalists (like dandelions and crabgrass) do thrive just about everywhere, giving them a competitive edge in disturbed habitats (like cities) where not much else grows, they get beaten by the specialists in old, stable ecosystems.  The specialists have evolved to tolerate those specific conditions better than anything else.

It's why in old-growth rain forests, just about everything you see -- plant and animal -- is a specialist.  Along roadside ditches, they're all generalists.

Some recent research suggests that this drive toward specialization in stable habitats is very old.  A study of the distribution of animals in Ediacaran (very late Precambrian) sandstone in Australia found that some of the peculiar animals characteristic of these ecosystems showed a distinct preference for particular parts of the habitat -- a clear hallmark of specialization.

The researchers focused on a handful of species that have no living descendants, including Obamus coronatus (which looks like a French cruller) and the hubcap-like Tribrachidium heraldicum, one of the only known animals to have triradial symmetry.

Artist's reconstruction of Obamus coronatus [Image licensed under the Creative Commons Nobu Tamura (http://spinops.blogspot.com/), Obamus NT, CC BY-SA 4.0]

Both animals were grazers, feeding on the microbial mat on the seafloor, but their habitat choices differed.  Obamus turned out to have a distinct preference for places where the mat was thickest; Tribrachidium was much more evenly dispersed.  And since both animals were of very low mobility -- similar to modern barnacles -- this didn't just reflect the chance arrangement of where they were when the a layer of sediment, probably stirred up by a storm or landslide, buried them for eternity.

This was a habitat choice -- and the first known example of specialization in the natural world.

"We think about the very oldest animals and maybe you wouldn't expect them to be so picky," said Mary Droser of the University of California - Riverside, who co-authored the study. "But Obamus only occurs where there is a thick mat, and it's a pretty sophisticated way of making a living for something so very old...  There are a limited number of reproductive strategies, especially for animals like these.  There are more strategies today, and they're more elaborate now. But the same ones used today were still being used 550 million years ago."

"It's not like studying dinosaurs, which are related to birds that we can observe today," said Phillip C. Boan, also of UC - R, and lead author of the new study.  "With these animals, because they have no modern descendants, we're still working out basic questions about how they lived, such as how they reproduced and what they ate...  This is really the first example of a habitat-selective Ediacaran creature, the first example of a macroscopic animal doing this.  But how did they get where they wanted to go?  This is a question we don't yet know the answer to."

It's fascinating that we can get some insight into the behavior of a species that lived so long ago, during a time where there was no life at all on land.  Imagine it -- everything alive is in the sea, and the continents were vast, barren expanses of rock, sand, and dust.  The first land-dwelling plants and animals wouldn't exist for another fifty million years (and even then, they were clustered around bodies of water; the central parts of the continents would have been lifeless for a great deal longer).  

But despite how alien this landscape would have seemed, organisms were already evolving through natural selection to have many of the same traits we see today -- including the fact that some of them, like modern orchids, know exactly where they want to be.

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The kludge factory

Know what a kludge is?

Coined by writer Jackson Granholm in 1962, a kludge is "an ill-assorted collection of poorly-matching parts, forming a distressing whole."  Usually created when a person is faced with fixing something and lacks (1) the correct parts, (2) the technical expertise to do it right, or (3) both, kludges fall into the "it works well enough for the time being" category.

[Image licensed under the Creative Commons Zoedovemany, Screen Shot 2015-11-19 at 11.54.48 AM, CC BY-SA 4.0]

Evolution is essentially a giant kludge factory.

At its heart, it's the "law of whatever works."  It's why the people who advocate Intelligent Design Creationism always give me a chuckle -- because if you know anything about biology, "intelligently designed" is the last thing a lot of it is.  Here are a few examples:

• Animals without hind legs -- notably whales and many snakes -- that have vestigial hind leg bones.
• Primates are some of the only mammals that cannot synthesize their own vitamin C -- yet we still carry the gene for making it.  It just doesn't work because it has a busted promoter.
• Human sinuses.  Yeah, you allergy sufferers know exactly what I'm saying.
• The recurrent laryngeal nerve in fish follows a fairly direct path, from the brain past the heart to the gills.  However, when fish evolved into land-dwelling forms and their anatomy changed -- their necks lengthening and their hearts moving lower into the body -- the recurrent laryngeal nerve got snagged on the circulatory system and had to lengthen as its path became more and more circuitous.  Now, in giraffes (for example), rather than going from the brain directly to the larynx, it goes right past its destination, loops under the heart, and then back up the neck to the larynx -- a distance of almost five meters.
• Our curved lower spines were clearly not "designed" to support a vertically-oriented body.  Have you ever seen a weight-bearing column with an s-bend?  No wonder so many of us develop lower back issues.
• One of the kludgiest of kludges is the male genitourinary tract.  Not only does the vas deferens loop way upward from the testicles (not quite as far as the giraffe's laryngeal nerve, admittedly), along the way it joins the urethra to form a single tube through the penis, something about which a friend of mine quipped, "There's intelligent design for you.  Routing a sewer pipe through a playground."  It also passes right through the prostate, a structure notorious for getting enlarged in older guys.  C'mon, God, you can do better than that.

The reason all this comes up is that the kludging goes all the way down to the molecular level.  A study from a team at Yale, Harvard, and MIT that appeared last week in the journal Science looked at the fact that when you compare the human genome to that of our nearest relatives, you find that one of the most significant differences is that our DNA has deleted sections.

That's right; some of why humans are human comes from genes that got knocked out in our ancestors.

The researchers found that there are about ten thousand bits of DNA, a lot of them consisting only of a couple of base pairs, that chimps and bonobos have and we don't.  A lot of these genetic losses were in regions involved in cognition, speech, and the development of the nervous system, all areas in which our differences are the most obvious.

The reason seems to have to do with gene switching.  Deleting a bit of switch that is intended to shut a gene off can leave the gene functioning for longer, with profound consequences.  Often these consequences are bad, of course.  There are some types of cancer (notably retinoblastoma) that are caused by a developmental gene having a faulty set of brakes.

But sometimes these changes in developmental patterns have a positive result, and therefore a selective advantage -- and we may owe our large brains and capacity for speech to kludgy switches.

"Often we think new biological functions must require new pieces of DNA, but this work shows us that deleting genetic code can result in profound consequences for traits make us unique as a species," said Steven Reilly, senior author of the paper.  "The deletion of this genetic information can have an effect that is the equivalent of removing three characters -- n't -- from the word isn't to create the new word is...  [Such deletions] can tweak the meaning of the instructions of how to make a human slightly, helping explain our bigger brains and complex cognition."

So yet another nail in the coffin of Intelligent Design Creationism, if you needed one.  Of course, I doubt it will convince anyone who wasn't already convinced; as I've observed more than once, you can't logic your way out of a belief you didn't logic your way into.

But at least it's good to know the science is unequivocal.  And, as astrophysicist Neil deGrasse Tyson said, "The wonderful thing about science is that it's true whether or not you believe in it."

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Parallel problem solving

One of the many fascinating aspects of evolution is how nature happens upon the same solutions to environmental problems, over and over.

Two of the best examples of this are eyes and wings.  True eyes evolved from simple photoreceptive spots at least four times: the vertebrate eye, with its complex system of lenses and retinas; the pinhole-camera eyes of the chambered nautilus and other cephalopods; the compound eyes of insects; and the rows of separate spherical eyes in clams and scallops.  Wings, on the other hand, evolved independently no fewer than six times: bats, birds, insects, pterosaurs, flying squirrels, and colugos (the last two count if you include gliding along with true powered flight).

The reason is simple.  There are a handful of problems animals have to overcome (perception/sensation, nutrition, reproduction, locomotion, avoiding environmental dangers, and avoiding predation) and a limited number of ways to accomplish them.  Once (for example) photoreceptive eyespots develop in an animal, natural selection for improving the sensitivity of those spots takes over, but how exactly you do that can differ.  The result is you end up with vision evolving over and over, and each time, the organ is structured differently, but accomplishes the same thing.

Evolution, it seems, is the law of whatever works.

This has interesting implications about what extraterrestrial life might look like.  I very much believe that certain features will turn out to be constrained in any conceivable species -- the presence of locomotor organs, organs sensitive to sound, light, heat, and touch, and so on -- but also, that the way those organs are arranged and configured could be very differently from anything we have on Earth.

This "multiple solutions to the same problems" idea is what immediately came to mind when my friend and fellow writer Gil Miller, whose inquisitive mind and insatiable curiosity have provided me with many a topic here at Skeptophilia, sent me a link from Phys.org about hollow bones in dinosaurs.  Endoskeletons such as our own exist in an interesting tension.  They have to be solid enough to support our weight, but the better they are at weight-bearing, the heavier they themselves are.  The mass of an animal in general increases much faster than its linear dimensions do; double a mouse's height, keeping its other proportions the same, and it will weigh about eight times as much.  This is why in order for the whole system to work, the proportions have to change as species increase in size.  A mouse's little matchstick legs would never work if you scaled it up to be as big as a dog; at the extreme end, consider the diameter of an elephant's legs in relation to its size.  Anything narrower simply wouldn't support its weight.

[Nota bene: this is why if you were traumatized when young by bad black-and-white horror movies about enormous insects wreaking havoc, you have nothing to worry about.  If you took, for example, an ant, and made it three meters long, its proportionally tiny little legs would never be able to lift it.  The worst it could wreak would be to lie there on the ground, helpless, rather than eating Tokyo, which is what the horror movie monsters always did.  One got the impression the inhabitants of Tokyo spent ten percent of their time working, relaxing, and raising families, and the other ninety percent being messily devoured by giant radioactive bugs.]

But back to the Phys.org article.  A detailed analysis of the bone structure of three different dinosaur lineages -- ornithischians, sauropodomorphs, and herrerasaurids -- found that while all three had landed on the idea of internal air sacs as a way of reducing the mass of their large bones, the structures of each are different enough to suggest all three evolved the feature independently.  Once again, we have an analogous situation to eyes and wings; identical problem, parallel solutions.  The problem here is that large body size requires heavy bones that require a lot of energy to move around, and the solution is to lighten those bones by hollowing them out (while leaving the interstices connected enough that they're still structurally sound).  And three different clades of dinosaurs each happened upon slightly different ways to do this.

Herrerasaurus ischigualastensis [Image licensed under the Creative Commons Eva Kröcher, CC-BY-SA]

It's fascinating to see how many ways living things happen upon similar solutions to the problems of survival.  Evolution is both constrained and also infinitely creative; it's no wonder we are so often in awe when we look around us at the natural world.  The "endless forms most beautiful and most wonderful" Darwin spoke of in the moving final words of The Origin of Species never fail to astonish -- especially since the brains we use to comprehend them are just one of the end products of those very same processes.

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Splitting the difference

One of the most misunderstood pieces of the evolutionary model is that natural selection is almost always a compromise.

Very few changes that could occur an organism's genes (and thus in its physical makeup) are unequivocally good.  (Plenty of them are unequivocally bad, of course.)  Take, for example, our upright posture, which is usually explained as having been selected for by (1) allowing us to see farther over tall grass and thus spot predators, (2) leaving our hands free for tool use, (3) making it easier to carry our offspring before they can walk on their own, or (4) all of the above.  At the same time, remodeling our spines to accommodate walking upright -- basically, taking a vertebral column that evolved in an animal that supported itself on all fours, and just kind of bending it upwards -- has given us a proneness to lower back injury unmatched in the natural world.  The weakening of the rotator cuff, due to the upper body no longer having to support part of our weight, has predisposed us to shoulder dislocations.

Then there are the bad changes that have beneficial features.  One common question I was asked when teaching evolutionary biology is if selection favors beneficial traits and weeds out maladaptive ones, why do negative traits hang around in populations?  One answer is that a lot of maladaptive gene changes are recessive -- you can carry them without showing an effect, and if you and your partner are both carriers, your child can inherit both copies (and thus the ill effect).  But it's even more interesting than that.  It was recently discovered that being a carrier for the gene for the devastating disease cystic fibrosis gives you resistance to one of the biggest killers of babies in places without medical care -- cholera.  It's well known that being heterozygous for the gene for sickle-cell anemia makes you resistant to malaria.  Weirdest of all, the (dominant) gene for the horrible neurodegenerative disorder Huntington's disease gives you an eighty percent lower likelihood of developing cancer -- offset, of course, by the fact that all it takes is one copy of the gene to doom you by age 55 or so to progressive debility, coma, and death.

So the idea of "selective advantage" is more complex than it seems at first.  The simplest way to put it is that if an inheritable change on balance gives you a greater chance of survival and reproduction, it will be selected for even if it gives you disadvantages in other respects, even some serious ones.

The reason the topic comes up is because of a cool piece of research out of the University of California - Santa Barbara into a curious genetic change in the charming little Colorado blue columbine (Aquilegia caerulea), familiar to anyone who's spent much time in the Rocky Mountains.

Colorado blue columbine (Aquilegia caerulea) [Image licensed under the Creative Commons Rob Duval, Heavycolumbinebloom, CC BY-SA 3.0]

Both the common name and scientific name have to do with birds; columba is Latin for dove, aquila Latin for eagle.  The reason is the graceful, backwards-curved tubular petals, which (viewed from the side) look a little like a bird's foot.  The tubes end in nectar glands, and are there to lure in pollinators -- mostly hummingbirds and butterflies -- whose mouthparts can fit all the way down the long, narrow tubes.

Well, the researchers found that not all of them have these.  In fact, there's a group of them that don't have the central petals and nectar spurs at all.  The loss is due to a single gene, APETALA3-3, which simply halts complete flower development.  So far, nothing too odd; there are a lot of cases where some defective gene or another causes the individual to be missing a structure.  What is more puzzling is that in the study region (an alpine meadow in central Colorado), a quarter of the plants have the defective flowers.

You would think that a plant without its prime method of attracting pollinators would be at a serious disadvantage.  How could this gene be selected strongly enough to result in 25% of the plants having the change?  The answer turned out to be entirely unexpected.  The plants with the defective gene don't get visited by butterflies and hummingbirds as much -- but they are also, for some reason, much less attractive to herbivores, including aphids, caterpillars, rabbits, and deer.  So it may be that the flowers don't get pollinated as readily as those of their petal-ful kin, but they are much less likely to sustain energy-depleting damage to the plant itself (in the case of deer, sometimes chomping the entire plant down to ground level). 

If fewer flowers get pollinated, but the ones that do come from plants that are undamaged and vigorous and able to throw all their energy into seed production, on balance the trait is still advantageous.

Even cooler is that the two different morphs rely on different pollinators.  Species of butterfly with a shorter proboscis tend to favor the spurless variant, while the original spurred morph attracts butterflies and hummingbirds with the ability to reach all the way down into the spur.  What the researchers found is that there is much less cross-pollination between the two morphs than there is between plants of the same morph.

For speciation to occur, there needs to be two things at work: (1) a genetic change that acts as a selecting mechanism, and (2) reproductive isolation between the two different morphs.  This trait checks both boxes.

So it looks like the Colorado blue columbine may be on the way to splitting into two species.

Once again, we have an example from the real world demonstrating the power and depth of the evolutionary model -- and one that's kind of hard to explain if you don't buy it.  This time, it's a pretty little flower that has vindicated Darwin, and shown that right in front of our eyes, evolution is still "creating many forms most beautiful and most wonderful."

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A genetic mixed bag

One of the subtlest features of the evolutionary model, and one often misunderstood even by people who understand and accept natural selection, is what we mean by "selective advantage."

On the surface, it's simple enough; any inheritable feature that confers longer, healthier life or more (and more vigorous) offspring.  The problem is, there are two twists on phenotype that make this a bit more complicated than it seems at first.

The first is that physical expression of genes is seldom unequivocally either good or bad for the organism.  The "unequivocally bad" ones are often discussed in introductory biology classes because they are simple; Tay-Sachs disease, for example, caused by inheriting a particular recessive allele from both parents, kills the brain cells and usually causes death by age four.  But most traits have good features and bad, so the question becomes, "Is this good for the organism on balance?"  One instance is our upright posture and bipedal gait.  It confers some advantages -- two of the more commonly-cited ones are leaving our hands free to manipulate tools, and giving us greater sight-distance for spotting predators.  (Nota bene: no one's sure which of those advantages led to our ancestors walking upright, or if it was something else entirely; saying "these are some of the advantages" is not the same as saying "these were the advantages that drove selection for this trait.")  The downside of upright posture, though -- given that we still have the basic spine shape as our knuckle-walking forebears -- is that humans have some of the worst lower back problems to be found in the animal world, with the only ones having it worse being Bassett hounds and dachsunds.

And the low-slung backs of Bassetts and wiener dogs are hardly the fault of natural selection.

Another complicating factor is pleiotropy -- which is that many genes have multiple effects, often only loosely related to each other.  The classic example of pleiotropy is the connection between coat and eye color, and inner ear development, in cats.  White, blue-eyed cats are frequently deaf -- the same gene that blocks pigment formation (and causes the white coat and blue eyes) hinders development of the cochlea, resulting in deafness.

What makes it even more complex is that sometimes a gene can have a drastically different set of effects depending on whether you have one copy (are heterozygous) or two (are homozygous).  It was long a puzzle of evolutionary science why some deleterious recessive genes are so common.  If having two copies of a gene kills you, effectively removing two copies of the allele from the gene pool, you'd expect the frequency of the allele to decrease over time.  So why do some really nasty genes stick around?

[Image is in the Public Domain]

Two examples where we've actually figured out the answer are the genes that cause cystic fibrosis (a horrible lung disease which is one of the more common serious genetic disorders in Caucasians) and sickle-cell anemia (an equally-dreadful blood disorder common in sub-Saharan Africans and African Americans).  While having two copies of either of those genes is certainly awful, having only one is beneficial, giving the individual an advantage over both the ones who have two bad copies and the ones who have two good copies of the allele.  In the case of cystic fibrosis, being heterozygous gives infants a significantly lower chance of contracting infantile diarrheal disease, which in cultures with limited access to medical care is a major killer of babies.  In sickle-cell anemia, having one copy of the allele gives you resistance to malaria -- so in malaria-ridden areas, homozygous recessive people die of sickle-cell anemia, and homozygous dominant people die of malaria.  Heterozygous individuals escape both.

Even seemingly unimportant genes can sometimes have unexpected effects.  It was long thought that the blood-type alleles -- nicknamed A, B, and O -- had no effect on anything other than blood transfusion compatibility.  It was recently discovered that the O blood type allele, which is the most common, confers resistance to smallpox.  So in areas that had smallpox epidemics, the individuals who were type A (the most susceptible allele) were much more likely to die, leaving the type Os at a significant selective advantage.  A map of the incidence of smallpox in Europe and a map of the frequency of the O blood type allele line up almost perfectly.

The reason all this comes up is because of a paper last week in the journal Development that looked at a rather horrifying genetic disorder called holoprosencephaly, where something interferes with prenatal forebrain development.  Affected children end up with malformed brains and multiple facial disfigurements -- cleft palate, cleft lip, and eyes that are extremely close together (in fact, sometimes they're fused).  These babies almost always die in utero.

Geneticists at the Max Delbrück Center for Molecular Medicine found two mutations that influenced the development of holoprosencephaly, which are called ULK4 and PTTG1.  Both of these genes regulate expression of the ultra-important sonic hedgehog gene, which is responsible for organ formation, nervous system development, and such fundamental features as symmetrical limb placement.  The researchers found that these two genes prevent holoprosencephaly, which you'd think would be enough of an advantage that it would eventually lead them to becoming fixed (everyone in the population being homozygous) except for rare cases of mutations.

Where it gets more interesting is that the researchers found that ULK4 and PTTG1 have other effects besides stopping holoprosencephaly in its tracks.  ULK4 is associated with schizophrenia and bipolar disorder -- and PTTG1 is linked to cancer.

So like cystic fibrosis and sickle-cell anemia, it's not as simple as saying "this allele is the good one, and this is the bad one."  And because both of the negative effects of ULK4 and PTTG1 affect individuals later in life, very likely after they have made the decision whether to have kids, the positive effect (surviving gestation) far outweighs the negative ones, at least from an evolutionary standpoint.

As I used to tell my AP Biology classes, "evolution doesn't really give a damn what happens to you after you've successfully procreated."  Harsh, but true in its essence.

So genetics and evolution are, like most things, a mixed bag.  They're a lot more complicated than they may seem at first, enough that it's kind of impressive researchers have been able to figure out how they work.  Considering what could potentially go wrong with development, I'm kind of blown away by how often things go right.  When my first wife found out she was pregnant, I spent the next eight or so months worrying, because I knew enough genetics to realize how bad things could be.  When my older son was born -- completely normal, except that he looks exactly like me, which is unfortunate but not fatal -- it was an incredible relief.

It may not be true that "a little knowledge is a dangerous thing," but sometimes it can be a bit stress-inducing.

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London in the nineteenth century was a seriously disgusting place to live, especially for the lower classes.  Sewage was dumped into gutters along the street; it then ran down into the ground -- the same ground from which residents pumped their drinking water.  The smell can only be imagined, but the prevalence of infectious water-borne diseases is a matter of record.

In 1854 there was a horrible epidemic of cholera hit central London, ultimately killing over six hundred people.  Because the most obvious unsanitary thing about the place was the smell, the leading thinkers of the time thought that cholera came from bad air -- the "miasmal model" of contagion.  But a doctor named John Snow thought it was water-borne, and through his tireless work, he was able to trace the entire epidemic to one hand-pumped well.  Finally, after weeks and months of argument, the city planners agreed to remove the handle of the well, and the epidemic ended only a few days afterward.

The work of John Snow led to a complete change in attitude toward sanitation, sewers, and safe drinking water, and in only a few years completely changed the face of the city of London.  Snow, and the epidemic he halted, are the subject of the fantastic book The Ghost Map: The Story of London's Most Terrifying Epidemic -- and How It Changed Cities, Science, and the Modern World, by science historian Steven Johnson.  The detective work Snow undertook, and his tireless efforts to save the London poor from a horrible disease, make for fascinating reading, and shine a vivid light on what cities were like back when life for all but the wealthy was "solitary, poor, nasty, brutish, and short" (to swipe Edmund Burke's trenchant turn of phrase).

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

The evolution of clumps

If humans operated by logic, rationality, and evidence, there would be arguments we would no longer be having.  A sampler:

• Climate change is real and the vast majority of the change we're seeing is caused by humans.
• Vaccines are safe, effective, and the risk of serious side effects is low.
• Trump lost.
• The Earth is an oblate spheroid.
• The biodiversity we see around us came about from evolution by natural selection.

The last one is the reason this topic comes up, even though -- as I've pointed out umpteen times -- there is zero doubt amongst biologists (and the majority of educated laypeople) that evolution occurred, and is still occurring.  As Richard Dawkins put it, you could instantaneously destroy every fossil in the world, and the remaining evidence for evolution would still be overwhelming.

But the subject resurfaces because of an elegant experiment I found out about because of a buddy of mine, that (should you still be on the fence, belief-in-evolution-wise) is the 3,948,105th nail in the coffin of the various anti-evolutionary models.  The study looks at multicellularity -- a step in the process of the evolution of complex life that has been a bit of a mystery.  We know it happened; there is a clear progression in Precambrian fossils from single-celled life forms to undifferentiated clumps of more-or-less identical cells to multicellular organisms with differentiated cell types, but exactly how it happened was unclear.

The study was led by Lutz Becks, biologist at the Limnological Institute of the University of Konstanz, and used a simple green algae (Chlamydomonas reinhardtii) to show that in short order, with the appropriate natural selection, multicellularity can evolve from a single-celled ancestor species.

C. reinhardtii does sometimes form clumps of cells, but they are usually small and transitory.  (Nota bene: remember that evolution doesn't create traits; it acts on variations that were already present in the population due to mutations.)  Becks and his team introduced a selective predator, the rotifer Brachionus calyciflorus, which is small enough to have a preference for individual algae cells and smaller cell groups.  The researchers then kept track of the proportion of single to multiple cells in the algae population, as well as the size of any multi-cell groups.

You've probably already guessed what happened.  The population of algae containing predators tilted toward becoming composed almost entirely of larger multicellular groups -- in only five hundred generations (which seems like a lot, but for algae that's only about six months).  Algae raised without the predator didn't change, remaining largely single-celled with a few smaller clumps scattered around.

What is coolest about this is that Becks and his team didn't stop there.  They took samples of the algae from both cultures and analyzed them genetically.  They found 76 different genes that showed significant differential expression between the two samples -- so not only were the traits of the population changing, the gene frequencies and activity were, as well.

Just as the evolutionary model predicts.

"We had actually expected that the formation of colonies can be achieved by different mechanisms in the algal cells and we would therefore find different mutations," Becks said, in an interview with Phys.org.  "In fact, we have seen a very high level of repeatability.  This suggests that the selection pressure has had a very targeted effect."

Keep in mind, too, that C. reinhardtii is an asexually-reproducing species -- so the cells are clones, and the only differences genetically are caused by mutations.  This should put to rest the nonsense that mutations can't create "new information" but only corrupt the "old information" that was already there.

In any case, here's yet another experiment supporting the fact that if a population has genetic variations and those variations are subject to a selecting agent, it will evolve.  Here, it's evolved fast enough to see it happening in real time.

Which would be convincing to the anti-evolutionists if they had any respect for evidence.  Which they don't.  So I'm not particularly hopeful that this will change the minds of the creationists and the intelligent-design cadre.  As Thomas Paine put it, "To argue with a man who has renounced the use and authority of reason is like administering medicine to the dead."

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I've loved Neil de Grasse Tyson's brilliant podcast StarTalk for some time.  Tyson's ability to take complex and abstruse theories from astrophysics and make them accessible to the layperson is legendary, as is his animation and sense of humor.

If you've enjoyed it as well, this week's Skeptophilia book-of-the-week is a must-read.  In Cosmic Queries: StarTalk's Guide to Who We Are, How We Got Here, and Where We're Going, Tyson teams up with science writer James Trefil to consider some of the deepest questions there are -- how life on Earth originated, whether it's likely there's life on other planets, whether any life that's out there might be expected to be intelligent, and what the study of physics tells us about the nature of matter, time, and energy.

Just released three months ago, Cosmic Queries will give you the absolute cutting edge of science -- where the questions stand right now.  In a fast-moving scientific world, where books that are five years old are often out-of-date, this fascinating analysis will catch you up to where the scientists stand today, and give you a vision into where we might be headed.  If you're a science aficionado, you need to read this book.

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

What doesn't kill you

In evolutionary biology, it's always a little risky to attribute a feature to a specific selective pressure.

Why, for example, do humans have upright posture, unique amongst primates?  Three suggestions are:

• a more upright posture allowed for longer sight distance, both for seeing predators and potential prey
• standing upright freed our hands to manipulate tools
• our ancestors mostly lived by the shores of lakes, and an ability to wade while walking upright gave us access to the food-rich shallows along the edge

So which is it?  Possibly all three, and other reasons as well.  Evolution rarely is pushed in a particular pressure by just one factor.  What's interesting in this case is that upright posture is a classic example of an evolutionary trade-off; whatever advantage it gave us, it also destabilized our lumbar spines, giving humans the most lower back problems of any mammal (with the possible exceptions of dachshunds and basset hounds, who hardly got their low-slung stature through natural selection).

Sometimes, though, there's a confluence of seeming cause and effect that is so suggestive it's hard to pass up as an explanation.  Consider, for example, the rationale outlined in the paper that appeared this week in Science Advances, called "Increased Ecological Resource Variability During a Critical Transition in Hominin Evolution," by a team led by Richard Potts, director of the Human Origins Program of the Smithsonian Institution.

What the paper looks at is an oddly abrupt leap in the technology used by our distant ancestors that occurred about four hundred thousand years ago.  Using artifacts collected at the famous archaeological site Olorgesailie (in Kenya), the researchers saw that after a stable period lasting seven hundred thousand years, during which the main weapons tech -- stone hand axes -- barely changed at all, our African forebears suddenly jumped ahead to smaller, more sophisticated weapons and tools.  Additionally, they began to engage in trade with groups in other areas, and the evidence is that this travel, interaction, and trade enriched the culture of hominin groups all over East Africa.  (If you have twenty minutes, check out the wonderful TED Talk by Matt Ridley called "When Ideas Have Sex" -- it's about the cross-fertilizing effects of trade on cultures, and is absolutely brilliant.)

Olorgesailie, Kenya, where our distant ancestors lived [Image licensed under the Creative Commons Rossignol Benoît, OlorgesailieLandscape1993, CC BY-SA 3.0]

So what caused this prehistoric Great Leap Forward?  The Potts et al. team found that it coincides exactly with a period of natural destabilization in the area -- a change in climate that caused what was a wet, fertile, humid subtropical forest to change into savanna, a rapid overturning of the mammalian megafauna in the region (undoubtedly because of the climate change), and a sudden increase in tectonic activity along the East African Rift Zone, a divergent fault underneath the eastern part of Africa that ultimately is going to rip the continent in two.

The result was a drastic decrease in resources such as food and fresh water, and a landscape where survival was a great deal more uncertain than it had been.  The researchers suggest -- and the evidence seems strong -- that the ecological shifts led directly to our ancestors' innovations and behavioral changes.  Put simply, to survive, we had to get more clever about it.

The authors write:

Although climate change is considered to have been a large-scale driver of African human evolution, landscape-scale shifts in ecological resources that may have shaped novel hominin adaptations are rarely investigated.  We use well-dated, high-resolution, drill-core datasets to understand ecological dynamics associated with a major adaptive transition in the archeological record ~24 km from the coring site.  Outcrops preserve evidence of the replacement of Acheulean by Middle Stone Age (MSA) technological, cognitive, and social innovations between 500 and 300 thousand years (ka) ago, contemporaneous with large-scale taxonomic and adaptive turnover in mammal herbivores.  Beginning ~400 ka ago, tectonic, hydrological, and ecological changes combined to disrupt a relatively stable resource base, prompting fluctuations of increasing magnitude in freshwater availability, grassland communities, and woody plant cover.  Interaction of these factors offers a resource-oriented hypothesis for the evolutionary success of MSA adaptations, which likely contributed to the ecological flexibility typical of Homo sapiens foragers.

So what didn't kill us did indeed make us stronger.  Or at least smarter.

Like I said, it's always thin ice to attribute an adaptation to a specific cause, but here, the climatic and tectonic shifts occurring at almost exactly the same time as the cultural ones seems far much to attribute to coincidence. 

And of course, what it makes me wonder is how the drastic climatic shifts we're forcing today by our own reckless behavior are going to reshape our species.  Because we're not somehow immune to evolutionary pressure; yes, we've eliminated a lot of the diseases and malnutrition that acted as selectors on our population in pre-technological times, but if we mess up the climate enough, we'll very quickly find ourselves staring down the barrel of natural selection once again.

Which won't be pleasant.  I'm pretty certain that whatever happens, we're not going extinct any time soon, but the ecological catastrophe we're increasingly seeming to be facing won't leave us unscathed.  I wonder what innovations and adaptations we'll end up with to help us cope?

My guess is whatever they are, they'll be even more drastic than the ones that occurred to our kin four hundred thousand years ago.

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Have any scientifically-minded friends who like to cook?  Or maybe, you've wondered why some recipes are so flexible, and others have to be followed to the letter?

Do I have the book for you.

In Science and Cooking: Physics Meets Food, from Homemade to Haute Cuisine, by Michael Brenner, Pia Sörensen, and David Weitz, you find out why recipes work the way they do -- and not only how altering them (such as using oil versus margarine versus butter in cookies) will affect the outcome, but what's going on that makes it happen that way.

Along the way, you get to read interviews with today's top chefs, and to find out some of their favorite recipes for you to try out in your own kitchen.  Full-color (and mouth-watering) illustrations are an added filigree, but the text by itself makes this book a must-have for anyone who enjoys cooking -- and wants to learn more about why it works the way it does.

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

An alpine gem in China

In order to produce new species -- so goes the evolutionary model -- you need two things: isolation (splitting off the population that will eventually become the new species from the parent population) and selection (environmental conditions that favor different traits in the splinter population than the ones favoring the parent population).  Given those two, and sufficient time, sooner or later you'll have two (or more) separate species.

The classic example of this, of course, is the group of birds called "Darwin's finches," that evolved from a parent population of tanagers from mainland South America (their closest relative is the Dull-colored Grassquit of Colombia, Ecuador, and Peru) something on the order of two million years ago.  Once arrived in the islands, they thereafter fragmented to fill the available niches in a process that has been nicknamed adaptive radiation.

So split off a population and give it some new conditions to contend with, and you'll end up with new species.  Which is what happened to a whole ecosystem's worth of species thirty million years ago -- leading to one of the most biodiverse spots on Earth.

New research into the genetics of the dozens of unique species in the Hengduan Mountains and Qinghai Plateau of western China has given us a fascinating lens into this process.  In "Ancient Orogenic and Monsoon-Driven Assembly of the World’s Richest Temperate Alpine Flora," by Wen-Na Ding, Robert Spicer, and Yao-Wu Xing of the Chinese Academy of Sciences and Richard Ree of Chicago's Field Museum, we read about a biotic province created by mountain building that not only raised the elevation (and thus lowered the average temperature), but altered wind currents to create monsoons -- and isolated the populations trapped there from their relatives on the other side of the mountain range.

"The theory is, if you increase the ruggedness of a landscape, you're more likely to have populations restricted in their movement because it's harder to cross a deeper valley than a shallow valley," said study co-author Richard Ree, in an interview with Science Daily.  "So any time you start increasing the patchiness and barriers between populations, you expect evolution to accelerate...  The combined effect of mountain-building and monsoons was like pouring jet fuel onto this flame of species origination.  The monsoon wasn't simply giving more water for plants to grow, it had this huge role in creating a more rugged topography.  It caused erosion, resulting in deeper valleys and more incised mountain ranges."

This all started back in the Oligocene Epoch, thirty million years ago, and the area has been pretty well isolated ever since.  The result is plants like the Himalayan lantern (Agapetes lacei):

.... which you wouldn't guess is a relative of rhododendrons and azaleas; the alpine monkshood (Aconitum gymnandrum):

... the gorgeous little Paraquilegia microphyllum:

... and literally hundreds of others, species found there and nowhere else on Earth.

The remoteness and general inaccessibility of the area has limited the human impact (fortunately), but scientists are rightly concerned with the effects that climate change will have on these subalpine valleys and plateaus.  Even if we're not directly damaging the ecosystem, our actions elsewhere imperil it, just as our out-of-control fossil fuel use has led to the thawing of the Arctic and the threat of ice sheet collapse in Antarctica -- the latter of which recent research has suggested could add three meters to the average sea level over a very short period, with catastrophic consequences.

But for now, let's just focus on this pristine gem of an ecosystem, and marvel at the processes that created it.  Once again, we see the truth of Darwin's words, with which he ended The Origin of Species: "There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved."

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This week's Skeptophilia book recommendation is a fun and amusing discussion of a very ominous topic; how the universe will end.

In The End of Everything (Astrophysically Speaking) astrophysicist Katie Mack takes us through all the known possibilities -- a "Big Crunch" (the Big Bang in reverse), the cheerfully-named "Heat Death" (the material of the universe spread out at uniform density and a uniform temperature of only a few degrees above absolute zero), the terrifying -- but fortunately extremely unlikely -- Vacuum Decay (where the universe tears itself apart from the inside out), and others even wilder.

The cool thing is that all of it is scientifically sound.  Mack is a brilliant theoretical astrophysicist, and her explanations take cutting-edge research and bring it to a level a layperson can understand.  And along the way, her humor shines through, bringing a touch of lightness and upbeat positivity to a subject that will take the reader to the edges of the known universe and the end of time.

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

Pieces of the mosaic

The diversity you find among birds is really remarkable.

There are differences in bill shape, from the weird angled beaks of flamingos, to the longer-on-the-bottom fish skewers of skimmers, to the absurd (and aptly-named) spoonbills and shoebills, to the pelicans -- about whom my dad taught me a limerick when I was little:

A wonderful bird is the pelican.
His bill can hold more than his bellican.
He can stash in his beak
All his food for the week,
But I really don't see how the hellican.

Yeah, it's kind of obvious where I got my sense of humor from.

Of course, it doesn't end there.  The impossibly long toes of the South American jacanas (called "lilytrotters" because they can walk on the floating leaves of waterlilies).  The phenomenal wingspan of the albatross.  The insane plumage of the birds-of-paradise.

And the colors.  Man, the colors!  Even in my decidedly non-tropical home we have some pretty amazing birds.  The first time I saw an Indigo Bunting, I was certain that one of my sons had put a blue plastic bird on the bird feeder just to rattle my chain.  There couldn't be a real bird that was that fluorescent shade of cobalt.

Then... it moved.

But nothing prepared me for the colors I saw on my visits to Ecuador, especially amongst the birds of the tanager family.  There are hundreds of species of tanagers in that tiny little country, and because they often travel in mixed foraging flocks, you can sometimes see twenty or thirty different species in the same tree.  These include the Green-headed Tanager:

[Image licensed under the Creative Commons Lars Falkdalen Lindahl (User:Njaelkies Lea), Green-headed Tanager Ubatuba, CC BY-SA 3.0]

The Black-capped Tanager:

[Image licensed under the Creative Commons Joseph C Boone, Black-capped Tanager JCB, CC BY-SA 4.0]

And the Flame-faced Tanager:

[Image licensed under the Creative Commons Eleanor Briccetti, Flame-faced Tanager (4851596008), CC BY-SA 2.0]

Being a biologist, of course the question of how these birds evolved such extravagant colors is bound to come up, and my assumption was always that it was sexual selection -- the females choosing the most brightly-colored males as mates (in this group, as with many bird species, the males are usually vividly decked out and the females are drab-colored).  If over time, the showiest males are the most likely to get lucky, then you get sexual dimorphism -- the evolution of different outward appearances between males and females.  (This isn't always so, by the way.  Most species of sparrows, for example, have little sexual dimorphism, and even experienced birders can't tell a male from a female sparrow by looking.)

The truth is, however, this is an oversimplified explanation, which I suppose I should expect given how long I've been in science.  Nature is both way more complex and way more interesting than we usually expect.  Just this week a paper was released in the journal BMC Evolutionary Biology that looks at another group of birds that look like someone went nuts with a paint-by-number set -- the Australasian lorikeets.

Lorikeets are in the parrot family, and even by comparison to other parrot species they're ridiculously flamboyant.  Take a look, for example, at the aptly-named Rainbow Lorikeet:

[Image licensed under the Creative Commons Dick Daniels (http://carolinabirds.org/), Rainbow Lorikeet RWD, CC BY-SA 3.0]

The researchers, Brian Smith, Glenn Seeholzer, and Jon Merwin of the American Museum of Natural History's Department of Ornithology, were curious about how lorikeets balance being bright enough to attract mates while not being so showy they attract the attention of predators -- the latter being in no short supply in Australia and New Guinea, where the birds are found.  Using spectral analyses of museum specimens encompassing nearly the entire diversity of lorikeets, Smith, Seeholzer, and Merwin found out a few things that were absolutely fascinating:

• Virtually all the color diversity in lorikeets is on the underside -- breast, abdomen, and front of the face.  The backs of almost all species are plain green -- making them camouflaged from above and less visible to predators like hawks.
• Some of the range of colors they do have is invisible to the human eye.  A number of species have pigments that reflect strongly in the ultraviolet region of the spectrum, which is visible to birds but not to us -- and presumably, not to many non-avian predators either.  So they can be as flashy as they want in the ultraviolet and still not attract attention from hungry carnivores.
• Each of the patches is under the control of a different set of genes and thus can be selected independently, meaning different species of lorikeets can diverge in terms of the facial color while remaining similar in the coloration on the back and abdomen -- something called "mosaic evolution."

"The range of colors exhibited by lorikeets adds up to a third of the colors birds can theoretically observe," Merwin said.  "We were able to capture variation in this study that isn't even visible to the human eye.  The idea that you can take color data from museum specimens, infer patterns, and gain a larger understanding of how these birds evolved is really amazing."

Of course, I wondered if the same forces might be involved in the evolution of two groups I've actually seen in the wild, hummingbirds and the aforementioned tanagers.  It certainly seems to fit the same pattern -- a wide range of eye-catching colors on the front of the body, and -- especially in the hummingbirds -- largely green on top.

But that's just a guess.  It certainly opens up an interesting line of inquiry into the evolution of other bird groups.  And -- perhaps -- will end up explaining a great many of the other pieces of the biodiversity mosaic.

*******************************

One of my favorite people is the indefatigable British science historian James Burke.  First gaining fame from his immensely entertaining book and television series Connections, in which he showed the links between various historical events that (seen as a whole) play out like a centuries-long game of telephone, he went on to wow his fans with The Day the Universe Changed and a terrifyingly prescient analysis of where global climate change was headed, filmed in 1989, called After the Warming.

One of my favorites of his is the brilliant book The Pinball Effect.  It's dedicated to the role of chaos in scientific discovery, and shows the interconnections between twenty different threads of inquiry.  He's posted page-number links at various points in his book that you can jump to, where the different threads cross -- so if you like, you can read this as a scientific Choose Your Own Adventure, leaping from one point in the web to another, in the process truly gaining a sense of how interconnected and complex the history of science has been.

However you choose to approach it -- in a straight line, or following a pinball course through the book -- it's a fantastic read.  So pick up a copy of this week's Skeptophilia book of the week.  You won't be able to put it down.

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

Sparkling camouflage

Natural selection is such an amazing driver of diversity.  As Richard Dawkins showed so brilliantly in his tour-de-force The Blind Watchmaker, all you have to have is an imperfect replicator and a selecting agent, and you can end up with almost any result.

The only requirement is that the change has to enhance survival and/or reproduction now.  Evolution is not forward-looking, heading in the direction of whatever would be a cool idea.  (It'd be nice if it were; I've wanted wings for ages.  Big, feathery falcon wings from my shoulders.  It'd make wearing a shirt impossible, but let's face it, I hate wearing shirts anyway so that's really not much of a sacrifice.)

Anyhow, the trick sometimes is figuring out what the benefit is, because it's not always obvious.  The extravagant tail of the peacock is clearly an attractant for females, although at this point the male peacocks may have maxed out -- reached the point where the tail's advantage of attracting females is counterbalanced by the disadvantage of being so cumbersome that it makes it harder to escape predators.  When two competing selecting agents hit that balance point, the species -- with respect to that trait, at least -- stops evolving.

A good bunch of the wild colorations you find in nature have to do with sex.  Not only attracting mates in animals, but colorful flowers attracting a specific pollinator -- because pollination is (more or less) plant sex.  But not all; the stripes of the Bengal tiger are thought to break up its silhouette in the dappled sunlight of its forest home, making it less visible to prey.  The bright colors of the dart-poison frogs are warning colorations, advertising the fact that they're highly poisonous and that predators shouldn't even think about it if they know what's good for them.  A recent study concluded that one advantage of stripes in the zebra is that it confuses biting flies, including the dangerous tsetse fly (carrier of African sleeping sickness) -- horses that were draped with striped cloth (mimicking the zebra's patterns) were far less susceptible to horsefly bites.  It's probable that the stripes also confuse predators such as lions, which frequently try to target one animal in a fleeing herd and separate it from the rest, a task that's difficult if the stripes make it hard to tell where one zebra begins and the other ends.  So zebra stripes may be a twofer.

Sometimes, though, the reason for a bright coloration isn't obvious.  In the summer here in upstate New York we often see brilliant little tiger beetles, named not for stripes (most of them don't have 'em) but for their role as a voracious predator of other insects.  The ones we have here are a glistening emerald green, which I always figured camouflaged them on plant leaves -- but there are ones that are an iridescent blue, and one species is green and blue with orange spots.

Hard to call that camouflage.

[Image licensed under the Creative Commons Ryan Hodnett, Six-spotted Tiger Beetle (Cicindela sexguttata) - Mississauga, Ontario 01, CC BY-SA 4.0]

Turns out that even the non-green ones might be using their sparkling colors as camouflage, however implausible that sounds.  A study that appeared this week in Current Biology, led by Karin Kjernsmo of the University of Bristol, concluded that the iridescence itself confuses predators, as much as it seems like it would attract attention.

Kjernsmo was studying the aptly-named Asian jewel beetles, which like our North American tiger beetles come in a wide range of glittering colors.  She took the wing cases of jewel beetles, both the iridescent and the matte species, and baited them with mealworms to see if birds had a preference.  85% of the targets with matte wings (of various colors) were picked off by birds, while only 60% of the iridescent ones were.

"It may not sound like much," Kjernsmo said, "but just imagine what a difference this would make over evolutionary time."

Her next question, though, was why.  This is much harder to determine, mostly because you can't ask a bird why it picked a particular insect for lunch.  (Well, you can ask.)  So what she did was a simple but suggestive experiment using human subjects -- she stuck various-colored wing cases to leaves at eye level on a forest trail, and had thirty-six human subjects walk the trail and see how many they could find.  They found 80% of the matte ones -- and only 17% of the iridescent ones!

It's a surprising result.  It may be that the shifting, sparkling surface of an iridescent insect confounds the ability of your visual cortex to make sense of what it's seeing by rendering it more difficult to perceive the edges, and therefore the shape, of what you're looking at.  The result: you can see the colors, but you don't recognize it as a beetle.  It's a plausible guess, but it will take more research to find out if it's the correct one, and if the reason the humans couldn't see iridescent wings is the same as why birds didn't eat them.

But once again, we're left with a slight difference in selection by a predator leading to what Darwin called "endless forms most beautiful and most wonderful."  The natural world is deeply fascinating, and is even more wonderful when you not only can appreciate its beauty -- but understand where that beauty may have come from.

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The brilliant, iconoclastic physicist Richard Feynman was a larger-than-life character -- an intuitive and deep-thinking scientist, a prankster with an adolescent sense of humor, a world traveler, a wild-child with a reputation for womanizing.  His contributions to physics are too many to list, and he also made a name for himself as a suspect in the 1950s "Red Scare" despite his work the previous decade on the Manhattan Project.  In 1986 -- two years before his death at the age of 69 -- he was still shaking the world, demonstrating to the inquiry into the Challenger disaster that the whole thing could have happened because of an o-ring that shattered from cold winter temperatures.

James Gleick's Genius: The Life and Science of Richard Feynman gives a deep look at the man and the scientist, neither glossing over his faults nor denying his brilliance.  It's an excellent companion to Feynman's own autobiographical books Surely You're Joking, Mr. Feynman! and What Do You Care What Other People Think?  It's a wonderful retrospective of a fascinating person -- someone who truly lived his own words, "Nobody ever figures out what life is all about, and it doesn't matter.  Explore the world.  Nearly everything is really interesting if you go into it deeply enough."

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