Category: evolution

Musings on Why Evolution is True (the book)

July 19, 2024 • 11:00 am

I had a couple hours to read last night, but didn’t want to start a fat novel as I’m leaving the country soon and wouldn’t want to schlep it. I thus picked up an old copy of God is Not Great, by Christopher Hitchens, which is a pretty quick read.  After two nights I’m almost half done with it, but am a bit disappointed because a lot of the science is wrong or outmoded (the latter is, of course, not Hitchens’s fault), and the arguments seem pretty repetitive.

On the other hand, I realize that these arguments were badly needed at the time and made a big impact on nonbelievers and believers alike. It’s one of the books that kick-started the “New Atheism,” and the “New” bit, as I always say, was the use of scientific arguments to rebut religions faith claims.  These arguments are amply in view in Hitchens’s book, and most of them are correct. And, of course, Hitch was a wonderful writer.

One of Hitchens’s arguments against creationism and its gussied-up cousin Intelligent Design is its invocation of vestigial organs like our vestigial tail, the appendix, wisdom teeth, and so on—all as evidence for evolution.  There were also examples of features that were jury-rigged by evolution so that they’re not perfectly adapted to their function: things like the backwards placement of the retina in the human eye, our “blind spot” where the optic nerve comes in, and—my favorite—the placement of the recurrent laryngeal nerve.

When I pondered those examples, I realized that IDers and creationists argue that all of these features are really adaptive.  The appendix, they say (correctly) contains a small number of cells that have immune functions, and the “backwards” retina of our camera eye is said by creationists to confer protection against an overload of short-wavelength light.  But of course whether the immune function of the appendix outweighs the fact that it may become infected and kill you is pure speculation, as is the postulated “useful” function of the backwards retina.

And I haven’t yet heard of an adaptive explanation for nipples in human males, our wisdom teeth, the developmental sequence of our kidney, or our transitory coat of hair in utero (the “lanugo”), but I’m sure that if you look hard enough on the Internet, you’ll find IDers and creationists showing how these aren’t really “senseless signs of history”, but are actually adaptive. And if they’re adaptive, then they reflect God’s plan.

In the end, I realized that the true purveyors of the “adaptationist program” aren’t evolutionary psychologists, but creationists, who aren’t willing to admit that the vagaries of evolution has vouchsafed us with featurs that, if there was a god or a Designer, could have been designed better. Further, they don’t often realize that if a “vestigial” structure is useful in some way, that doesn’t disprove that it had an evolutionary origin. The “halteres”—balance organs of some insects—is one example. They are used for keeping a guided flight, but we know that they are the vestigial remnants of wings, derived from two of the four wings that flying insects used to have. And they’re useful!

I won’t dwell on this, as these things are discussed in detail in my book Why Evolution is True, and you can also see many examples of vestigial organs supporting evolution at Douglas Theobald’s great site, “29+ evidences for macroevolution” (there are multiple pages; vestigial organs, atavisms, and other features testifying to evolution are here).

Finally, I have never seen creationists even try to refute the biogeographical evidence for evolution, like the absence of endemic mammals, fish, and amphibians on oceanic islands (islands that rose, bereft of life, from the sea bed) as opposed to continental islands that were once connected to continents. Biogeography is the true Achilles Heel of both creationism and ID.

I’m often asked if I’ve though about rewriting or updating my first trade book,  Why Evolution is True. My answer is always “no”—mainly because there’s enough evidence in that book to convince any rational person of its title’s assertion. But I suppose that if I did revise it, I would update it with more evidence for evolution, especially from fossils and molecular biology.  I do present plenty of fossil evidence for evolution in the book, and also some molecular evidence. The latter includes the presence of “dead genes” (genes that were functional in our ancestors and in some of our relatives, but have been rendered nonfunctional in us by degrading mutations). Examples are our many dead “olfactory receptor genes, active in dogs but totally inactive in whales, or a dead gene that is key in synthesizizing Vitamin C in other mammals. That gene is defunct, an ex-gene that sings with the Choir Invisible, but its death doesn’t harm because we get the vitamin from our diet.  I see no way that creationists or IDers can explain the fact that our DNA is largely junk, and much of that junk consists of dead genes. Loading our DNA with genes that don’t do anything, but still have to be copied during cell division and meiosis, is a lousy way to design a genome.

But now we have more such evidence, Here’s Ken Miller lecturing on some of the molecular/chromosomal evidence for evolution in humans and other primates from the structure of our chromosome 2.

I don’t mention this in my book, but it’s a convincing bit of evidence that we’re related to other primates.

There’s a lot of stuff like this, but I won’t belabor it now.  The short take is that I don’t think WEIT (the book) needs to be revised because it would just pile additional evidence for evolution on the Everest of evidence that already exists.  The fact is that evidence from a variety of different disciplines—paleontology, developmental biology, morphology (vestigial organs), biogeography, and molecular biology—all cohere to attest to the truth of evolution. IDers will admit of some microevolution, and even some macroevolution, but the more weaselly ones simply play a “god of the gaps” game, saying that there are adaptations that simply could not have evolved via a step-by-step Darwinian process of accumulating helpful mutations.  (The bacterial flagellum used to be one, but has fallen in light of later research.)

Asserting that our ignorance proves the existence of a Designer has never been a good strategy for researchers. It is simply a “science stopper”, implicitly saying, “You don’t need to do any more research; I already know that this phenomenon is inexplicable by materialistic processes and therefore is evidence for supernatural design.”  How many assertions like that have been debunked by later evidence? The answer is TONS OF THEM.

And I need hardly add that unless we have independent evidence for such a designer, we can simply ignore arguments that depend on its existence.

An open letter to Noa Tishby: the persisting trauma of Jews is not in our genes

July 17, 2024 • 11:00 am

This is an open letter to Noa Tishby because, as a passionate defender of Israel, she made a rather serious mistake about biology, and I tried to contact her about it via her publicist. I don’t know if she got my email, so I’m putting it below lest any Jews (or other people) be led to that we carry genes for inherited trauma.  We almost certainly don’t!

Noa Tishby is an Israeli actress who moved to the U.S. and has largely given up acting to advocate for Israel, in which she’s done an exemplary job. She wrote, for example, a primer for the ignorant called Israel: A Simple Guide to the Most Misunderstood Country on Earth, setting out the background of the conflict between Israel and, well, the rest of the world. I read it, and although I already knew much of the material, many people don’t, as evidenced by the widespread and often willful ignorance among “anti-Zionists.” See the first video below!

Noa’s also got chutzpah, as you can tell from this video. She is not easily fazed or discombobulated, even when faced with arrogant stupidity combined with hatred:

In other words, I’m a fan and admire her resolve.

Her error: In the article below, published in the Jewish magazine Sapir, Tishby describes how nerdy she was when young, and now her “uncoolness” persists in her constant defense of Israel, an unpopular stand in much of the world.  While making this reasonable argument, though, Tishby also made a misguided claim about the “inherited” trauma of Jews. It’s a good article (click to read), but the epigenetics stuff bothered me.

Here’s the part that rankled:

What haunts us, even those of us who have lived through only the most recent pogrom, is the familiarity of even the oldest testimony. “We were awakened by a terrifying noise, we didn’t know what was happening . . . ” two millennia ago in Jerusalem. “We realized they’d broken into our neighbors’ house. . . .  We heard them screaming until silence fell. We thought of escaping into the forest, but everyone who tried to escape found it was impossible” one millennium ago in Cologne. This history has shaped us: “Deep inside I know it,” each survivor says in unison as they stand together at the close of the video. The weight of our past is in our blood.

Perhaps literally. Recent studies suggest that these traumatic stories have become woven into our hereditary fabric through epigenetic change. Epigenetic changes are additions to our DNA that influence the way our genetic code is read by our bodies. Studies show that epigenetic change can occur from traumatic experience, and that these changes can be inherited. The idea is intuitive to us: It’s long been suggested that historical traumas can be psychologically passed down from generation to generation. Epigenetic fear is the biological manifestation of historical traumas alongside our genetic code. A review found that “there is now converging evidence supporting the idea that offspring are affected by parental trauma exposures occurring before their birth, and possibly even prior to their conception.” One study found that “in the absence of their own traumatic exposures, offspring of Holocaust survivors” were more likely to exhibit biological signs associated with post-traumatic stress disorder (PTSD). Other studies have suggested that epigenetic changes can be passed down for many generations.

After the pogrom of October 7 and the global reactions to it, our epigenetic inheritance may have been activated in our veins. As the researcher behind the study of offspring of Holocaust survivors observed, “Epigenetic changes often serve to biologically prepare offspring for an environment similar to that of the parents.”

In this respect, Jews have a built-in mechanism that gives acts of barbarism against us a certain familiarity and triggers an almost automatic response. Though the threats have come from different neighbors — Romans, Germans, Baghdadis — across time and place, they have always been similar enough to inoculate us against being truly surprised.

Here’s another version of it on her Facebook page.

Now if you know anything about epigenetics, a form of inheritance of acquired characteristics, you’ll know two things.  First, in nearly all organisms the acquired trait gets passed on for only a single generation, as the modifications of DNA that cause the trait (in this case trauma), is wiped out as the DNA sheds its modifications when producing gametes for the next generation.  Second, there is no evidence that I know of in mammals (including us) that even if a trauma causes something to be inherited by modifying our DNA, that “something” is not the trauma itself, but whatever developmental change happens to be wrought by environmental effects on the DNA.  In the most famous widespread case of “inherited trauma”, the Dutch case of famine during the “hunger winter” of 1944, what was inherited wasn’t the trauma of not getting enough food, but a number of developmental aberrations that lasted only a single generation:

The Dutch Hunger Winter has proved unique in unexpected ways. Because it started and ended so abruptly, it has served as an unplanned experiment in human health. Pregnant women, it turns out, were uniquely vulnerable, and the children they gave birth to have been influenced by famine throughout their lives.

When they became adults, they ended up a few pounds heavier than average. In middle age, they had higher levels of triglycerides and LDL cholesterol. They also experienced higher rates of such conditions as obesity, diabetes and schizophrenia.

By the time they reached old age, those risks had taken a measurable toll, according to the research of L.H. Lumey, an epidemiologist at Columbia University. In 2013, he and his colleagues reviewed death records of hundreds of thousands of Dutch people born in the mid-1940s.

They found that the people who had been in utero during the famine — known as the Dutch Hunger Winter cohort — died at a higher rate than people born before or afterward. “We found a 10 percent increase in mortality after 68 years,” said Dr. Lumey.

The change lasted only one generation; as far as I know, the grandchildren of survivors don’t show this syndrome. Thus, Ms. Tishby erred when implying that the trauma itself faced by Jews could presumably last for a long time, perhaps generations.  If we are indeed traumatized by centuries of antisemitism, it’s certainly because the trauma comes from the environment (i.e., antisemites), and persists because antisemitism persists. Certainly I didn’t want a famous defender of Israel to popularize misguided biology.

So I sent the letter below a while back to Ms. Tishby. Since I couldn’t find a way to contact her directly, I sent it to her public relations person with a request that it be passed on to Tishby. So far I have no reply, and though I didn’t expect one from Tishby, I have no way to know if she ever got my correction.  Ergo I’m publishing it here in hopes that she’ll see it and the “inherited trauma of antissemitism” business will stop.  Yes, call me a Pecksniff. . .

Dear Ms. Tishby,

I’m writing just to urge you to be a bit cautious about the “epigenetic” aspect of Jewish trauma that you mentioned in your otherwise admirable Sapir article. I’m only writing because I’ve long admired your advocacy of Israel in the face of huge pushback, and don’t want you to fall into the errors of others who have mischaracterized epigenetics.

I am Jewish and also an evolutionary geneticist, and know a great deal about epigenetics: environmentally-induced changes in the DNA that usually occur by attaching a methyl group to various parts of DNA. It’s been known, as you said, that this can be inherited: rarely, the effects of parental trauma can cause inherited change in their offspring, though those changes don’t usually involve a child inheriting the trauma itself of their mothers.

What’s more important is that, because DNA changes are “reset” every generation when sperm or eggs are formed, epigenetic modifications usually disappear after one generation, so they can’t be inherited beyond parent—>offspring.  Further, if they do occur (usually through trauma affecting a mother’s physiology or placenta), what is inherited via methylation is not the trauma itself, but various other effects. The famous “Dutch famine study” from the “hunger winter” during the war didn’t involve inheritance of trauma, but a degradation of the offspring’s health that led to various other diseases. In other words, trauma was not inherited, but caused other effects in the children of the traumatized. And that lasted but a single generation.  There’s simply no evidence in humans that trauma itself can be coded into the genome and passed from parent to offspring.

You also mention that ” Other studies have suggested that epigenetic changes can be passed down for many generations.” But the study you cite involved roundworms, and had nothing to do with either humans or trauma (only one study, not “studies” was linked).

In short, there are no studies showing that parental trauma itself is inherited epigenetically. Instead, the effects of trauma on the physiology or development of offspring can be inherited. But they’re inherited, at most, for only one generation. Ergo, it’s a bit misleading to suggest that “the weight of the past is in our blood—literally.” That would be true only, and only in part, for the one generation of offspring of those experiencing the Holocaust. The rest of the Jews would be unaffected, so it wouldn’t be a general phenomenon.  And it would last only for a single generation at most—and what would be inherited wouldn’t be trauma itself but whatever developmental aberrations devolved upon fetuses developing during their mother’s trauma.

It’s really not necessary to invoke dubious science in support of your cause, for we Jews have suffered environmental trauma generation after generation via antisemitism, and this is due to a continuing culture, not to genes.  I myself have been traumatized by the resurgence of antisemitism after October 7, even though I’m at best a secular Jew. But none of my relatives were in the Holocaust, though they came from Eastern Europe.  My own “trauma” comes from seeing the world buy into the big lies about Israel (genocide, apartheid, “disproportinal” killing of Gazans, etc.)

My suggestion, then, is to stay far away from epigenetics as you promulgate your message. And of course your message is vital and important. As I said, I greatly admire your courage in going out there and speaking the truth, and wanted to let you know that the “truth” about epigenetics isn’t very solid!

Best wishes,
Jerry Coyne
Emeritus professor of Ecology and Evolutino
The University of Chicago

I’ve done what I can, and we’ll see if Ms. Tishby continues to spread the fallacious notion of “trauma literally in our blood” (it would have to be in the white cells, since red blood cells lack nuclei!)

New paper puts the “last universal common ancestor”: the creature that gave rise to all living things, much earlier than previously thought: 4.2 billion years.

July 17, 2024 • 9:30 am

A brand-new paper from Nature Ecology & Evolution used a clever technique to estimate the age of “LUCA”,. the “last universal common ancestor” of all living things. What that means is LUCA is the last creature whose descendants include every species alive: the ancestor of all of us.  And it dates LUCA to about 4.2 billion years ago! That is far older than people thought. Previous estimates were in the 3.5-3.8 billion-year range, after the famous “Late Heavy Bombardment” (LHB), during which the Earth was continually battered with asteroids and comets. It was assumed that nothing alive on Earth could have survived those impacts. But if the authors are right, LUCA’s ancestors did survive this, for 4.2 billion years is probably a big underestimate of of when life on earth began.

The earliest generally accepted fossil evidence for life is about 3.7 billion years, which is based on isotopes that, scientists think, could have been produced only by living creatures. But the earliest genuine fossilized organisms occur a bit later than that: fossilized blue-green algae (“stromatolites”), whose fossils go back 3.5 billion years ago.

The new paper by Moody et al., which has an accompanying research brief (click screenshots below to access, or find the pdf here) pushes the age of LUCA back to 4.2 billion years ago, which actually precedes the LHB. And the new LUCA date comes soon after the Earth actually formed (about 4.54 billion years ago) and after the Moon was created, probably by a huge, Mars-size planet striking Earth and throwing off debris that consolidated to create our Moon. (That occurred soon after the Earth formed.)  Surely no life could have survived that collision, so if the authors are right, it took only about  0.3 billion years, or 300 million years after the Earth was formed, before life existed.

But LUCA wasn’t the first life on Earth: it is simply the bacteria-like species of organism that gave rise to all living creatures. Surely life originated before that, and the new paper suggests that the 4.2 billion year old (byo) LUCA was only one of a number of life forms existing back then, with the rest going extinct without leaving descendants. The authors think this because LUCA probably needed complex carbon compounds to live, and is also likely to have provided niches for other creatures.  That means that life itself began well before LUCA, especially because, based on its genome, the authors conclude that LUCA was quite complex— about as complex as modern bacteria. Surely it would take millions of years of evolution to get to the point where a LUCA-like creature could have existed.  See below for the diagram of what LUCA was like.

The main lesson from the paper is that life began very, very soon after the Earth had cooled off and the dust had settled from the LHB and carving out of the Moon. If that’s the case, then perhaps life on other planets could evolve more easily than we thought.

But on to the paper. If you want the whole megillah, click on the first link, while the second gives a two-page précis.  It’s a very complicated and long paper, so give me kudos for reading it twice to distill it here. But I can’t claim to have understood everything, as the analyses of the data, or even the methodology, is quite arcane and sophisticated.

A two -age summary from the same journal:

Why do we think that all life descended from a single species rather than having multiple origins? Because all living creatures have some similarities that probably reflect the workings of chance: whatever mutations happened to give rise to our ancestor. The paper explains:

The common ancestry of all extant cellular life is evidenced by the universal genetic code, machinery for protein synthesis, shared chirality of the almost-universal set of 20 amino acids [JAC: all amino acids used in modern creatures are the L rather than the D form] and use of ATP as a common energy currency. The last universal common ancestor (LUCA) is the node on the tree of life from which the fundamental prokaryotic domains (Archaea and Bacteria) diverge. As such, our understanding of LUCA impacts our understanding of the early evolution of life on Earth.

The way scientists usually estimate LUCA is using molecular dating based on DNA divergence among living organisms. Because there is a “molecular clock”, with the DNA changing roughly in a linear fashion with time, you can back-calculate from living creatures to estimate when their DNA sequences would have converged on a single sequence, which would be the DNA sequence of LUCA.  But there are formidable problems with this, making DNA-based estimates  contentious. But the authors found a way around this.

What they did is to estimate divergence times of all living creatures (for practicality, they used bacteria [prokaryotes] and Archaea, bacteria-like organisms that form their own kingdom) using DUPLICATED GENES.  These are genes that, tracing the sequences of living organisms back, had already been duplicated in LUCA.  As you may know, genes often get duplicated during cell division or (in sexual organisms) meiosis, so a single gene can now occur in two copies. Those two copies will initially be identical, but then, being genetically independent, will begin to diverge via mutation and then selection or drift. (Examples of duplicated genes are are different forms of globins in humans, two of which, alpha and beta, produce products that combine to make adult hemoglobin.  But many, many genes have duplicated over the history of life.)

A gene that is duplicated (based on sequence similarity) in LUCA must have been present in the ancestor of LUCA, and have duplicated before LUCA existed. Thus an estimate of the age of a duplicated gene in LUCA gives us a lower-bound on the age of LUCA itself. And since some genes are already duplicated in LUCA, we can use them, combined with a molecular clock (and other statistics) to estimate how long it took for each copy to give rise to the diversity of DNA-sequences in descendant copies in modern microbes.  The advantage comes because we have two estimated DNA sequences in LUCA that began identically but then diverged over evolutionary time. This gives us two chances to estimate the age of the creature. Using other methods, we can estimate how many genes there were in LUCA, the size of its genome, and what kind of genes it had.  The latter can then give us an idea of what kind of creature it was and how it lived.

Here are the results, in short:

a.) LUCA lived about 4.2 billion years ago. Here’s the reconstructed phylogeny (note that there are two estimates of its age since they use two copies of each of the five genes they chose for age estimation). Click to enlarge. On the right are all the kingdoms of living organisms, traced back to LUCA.  The use of two gene copies give similar estimates, about 4.2 billion years ago. I’ve circled the two LUCA estimates, which work out to a similar age (see age scale at top for divergence times):

(From paper): Our results suggest that LUCA lived around 4.2 Ga, with a 95% confidence interval spanning 4.09–4.33 Ga under the ILN relaxed-clock model (orange) and 4.18–4.33 Ga under the GBM relaxed-clock model (teal). Under a cross-bracing approach, nodes corresponding to the same species divergences (that is, mirrored nodes) have the same posterior time densities. This figure shows the corresponding posterior time densities of the mirrored nodes for the last universal, archaeal, bacterial and eukaryotic common ancestors (LUCA, LACA, LBCA and LECA, respectively); the last common ancestor of the mitochondrial lineage (Mito-LECA); and the last plastid-bearing common ancestor (LPCA). Purple stars indicate nodes calibrated with fossils. Arc, Archaea; Bac, Bacteria; Euk, Eukarya.

b.) LUCA had a big genome and many genes. The authors estimate that LUCA’s genome had 2.75 million DNA base pairs, capable of making 2,657 proteins (an underestimate of gene number). That is a big and complex organism, comparable to existing bacteria. (Modern E. coli produce about 4288 proteins from 4.6 million base pairs.) This complexity shows that even LUCA was preceded by a long period of evolution.

c.) LUCA was probably an anaerobic and autotrophic creature, which means that it didn’t need oxygen to grow and flourish, and also that it produced its own “food”, getting energy from substances like hydrogen and carbon dioxide.  The authors suggest two places where such a creature could have lived: in warm hydrothermal vents in the ocean, or on the ocean surface, where it would have ample access to the gases that constitute its food.  There was no evidence that the organism was photosynthestic, as it lacked genes involved in modern photosynthesis.

Here’s a sketchy diagram of what kind of genes LUCA had (note the “immune” system, based on CRISPR-like genes that are used to destroy viruses. LUCA probably had a virus problem, too! Figure b) show us how LUCA fit into the tree of life:

(From paper): a, A representation of LUCA based on our ancestral gene content reconstruction. Gene names in black have been inferred to be present in LUCA under the most-stringent threshold (PP = 0.75, sampled in both domains); those in grey are present at the least-stringent threshold (PP = 0.50, without a requirement for presence in both domains). b, LUCA in the context of the tree of life. Branches on the tree of life that have left sampled descendants today are coloured black, those that have left no sampled descendants are in grey. As the common ancestor of extant cellular life, LUCA is the oldest node that can be reconstructed using phylogenetic methods. It would have shared the early Earth with other lineages (highlighted in teal) that have left no descendants among sampled cellular life today. However, these lineages may have left a trace in modern organisms by transferring genes into the sampled tree of life (red lines) before their extinction. c, LUCA’s chemoautotrophic metabolism probably relied on gas exchange with the immediate environment to achieve organic carbon (Corg) fixation via acetogenesis and it may also have run the metabolism in reverse.

d.) LUCA was part of a community of other organisms.  It’s inconceivable that LUCA. which was a sophisticated organism, could live without a source of organic compounds (like amino acids) to use for constructing its body (remember, these organic compounds were not a “food,” but a construction material). Further, LUCA would itself provide organic compounds that would create niches for other species. (It’s likely that viruses, which aren’t good candidates for a LUCA-like creature, already existed.) The phylogeny in figure (b) just above shows how LUCA would fit into the tree of life, giving rise to all modern creatures via speciation  events, but would itself also be part of an earlier family tree, all of whose members save LUCA went extinct without leaving descendants.

These are the four big conclusions of the paper, with the most interesting to me being how short the time was after Earth’s formation for complex life to have evolved.  And the age of LUCA, remember, is an UNDERESTIMATE of how long it took complex life to evolve after the Earth’s conditions were suitable for such evolution.

I’ll end with the authors’ own conclusions, which are lucid enough for the layperson (bolding is mine)

Conclusions:

By treating gene presence probabilistically, our reconstruction maps many more genes (2,657) to LUCA than previous analyses and results in an estimate of LUCA’s genome size (2.75 Mb) that is within the range of modern prokaryotes. The result is a picture of a cellular organism that was prokaryote grade rather than progenotic  [JAC: not having the characteristic of a prokaryote, which LUCA did] and that probably existed as a component of an ecosystem, using the WLP [JAC: the Wood-Ljungdahl pathway for producing energy, based on hydrogen and carbon dioxide] for acetogenic [JAC: producing acetate as a product of anaerobic metabolism] growth and carbon fixation. We cannot use phylogenetics to reconstruct other members of this early ecosystem but we can infer their physiologies based on the metabolic inputs and outputs of LUCA. How evolution proceeded from the origin of life to early communities at the time of LUCA remains an open question, but the inferred age of LUCA (~4.2 Ga) compared with the origin of the Earth and Moon suggests that the process required a surprisingly short interval of geologic time.

Oh, and the authors suggest the intriguing possibility that if we could reconstruct the DNA sequence of LUCA—something that is not beyond the realm of possibility—then perhaps we could perhaps make in the lab a LUCA-like organism, and actually see what our ancestor looked like!

Bret Weinstein embarrasses himself again, disses modern evolutionary biology for not understanding everything, osculates Intelligent Design

June 24, 2024 • 9:30 am

I’m tired of Bret Weinstein pushing conspiracy theories, and just as tired of him making proclamations about evolutionary biology that are misleading or flat wrong.  I’m especially peeved today because, in the video below, he claims that both Richard Dawkins and I have said that “evolution biology is settled” because I, at least, claimed that the big advances at the beginning of the field, involving people like Darwin, Fisher, Haldane, Sewall Wright, and Ernst Mayr, established the foundations of the field, and we don’t see such big advances any more.  Where are today’s Darwins? (This was a question posed to me by Dick Lewontin when I interviewed him some years ago.) And yes, I probably said that and do believe it. But that doesn’t mean that evolutionary biology is “settled”. It’s that our approach to understanding evolution in nature has been somewhat asymptotic, with a big leap at the beginning and then incremental progress since the 1940s.  Indeed, I think that advances such as the “modern synthesis” of the 1930s and 1940s, showing that Darwinian natural selection was compatible with modern genetics, was a huge synthesis that hasn’t been equaled. And, of course, science of any sort never reaches an asymptote, for that would be “complete understanding: the ultimate truth,” which is unattainable.

In the video below, Weinstein and Heying argue that Dawkins and I think that evolutionary biology is “settled,” and that our view impedes progress in the field, allows evolutionary biology to stagnate, and, most important, impedes people’s failure to take Intelligent Design theory seriously for raising serious problems with neo-Darwinism.  Further, he says that we’ve discouraged graduate students from entering the field and have not produced, as mentors, our “replacements.” He’s dead wrong here, at least for me: I’d put my graduate students (and their graduate students) up against anybody’s as having made substantial progress in evolutionary genetics.

Yes, we have nobody around today who’s made advances as big as those of Darwin or Fisher. But that doesn’t mean at all, as Weinstein and Heather Heying assert in the video below, that we think evolutionary biology is “settled.”  Far from it! First of all, neutral theory was a big step forward in evolutionary genetics, and that was introduced in 1968 and is still being developed.  We still don’t understand exactly why organisms reproduce sexually; we don’t understand how often speciation occurs without geographic isolation; we don’t understand what females, during sexual selection, are looking for when they choose a mate. I could list tons of other questions, but these are three that I’ve written about and are mentioned by Weinstein.

Weinstein and Heying’s claim in the video is that there are huge advances, on the scale of Darwin’s and Fisher’s, to be made, perhaps by people who are working in intelligent design. (Weinstein implies that he has a theory that may be on this scale as well.) To be sure, they note that the IDers like Stephen Meyer and his “high-quality colleagues”, are motivated by religion, but Weinstein sees them still asking important and serious questions that evolutionists haven’t answered, thus motivating evolutionists to better understand nature.  Nope. ID adocates have wasted the time of evolutionists in refuting IDer’s specious arguments. Why do they do this? To let the credulous public, much of which buys ID, know that science can answer those criticisms.  That’s why there were so many critiques of Michael Behe’s books by reputable scientists.

Three questions that evolutionists have supposedly set aside and neglected are these: “What caused the Cambrian explosion?”, “Why are there gaps in the fossil record?” and “How can we get complex working proteins when their existence is so improbable?”

The answer to the first question is “We don’t know, but there are theories and some of them are being tested.”

The second question has a spate of possible answers (lack of sediment deposition, rapid evolution in relatively short evolutionary times, and so on). But one thing we know is that Gould’s explanation—the theory of punctuated equilibrium—is not likely to be the answer, as the theory doesn’t work. (People don’t often realize that punctuated equilibrium, as advanced by Gould and Eldredge, is more than just a jerky pattern in the fossil record: it’s also a theory about why the pattern is supposedly ubiquitous. The ubiquity of the pattern in fact is still being argued, but we know that it’s not ubiquitous.) But in the end, Gould’s explanation—the really novel and non-Darwinian part punctuated equilibrium—was simply wrong.

As for the third question, the claim that the origin of complex proteins is improbable is not one taken seriously by molecular evolutionists, simply because we have no indication that it really is a problem. The idea that it is a problem comes from specious claims of IDers that such proteins assemble themselves randomly rather than by selection, or that mutation is too unlikely to fuel the process (there are other fuels, of course, like gene duplication and insertions of DNA).

At 2:56, in the video below, Weinstein asserts that evolutionary biologists have simply left the Big Questions “on the table”, questions like “where did all the species come from?” and “why do females put males in so many species to challenges that then cause them to burden their male offspring with elaborate displays that are not helpful?”

Weinstein is apparently unaware that I wrote a comprehensive and scholarly book on speciation in 2004 and outlined a lot of unanswered questions, so no, Dr. Weinstein, I did NOT think that the question “wasn’t worthy of my time”. And yes, we do have considerably more understanding these days about how species form. That’s also described in the book.

He’s also apparently unaware that many biologists have been working on sexual selection, which is simply a hard problem to test in nature. And he doesn’t understand that elaborate displays by males are helpful: they help males get mates. Peacocks with more “eyes” in their tails, for example, get more offspring. Widowbirds whose tails are artificially elongated by gluing on extra feather get more mates, too.  Weinstein is ignorant about how sexual selection works, and how theories about it have been tested.

At any rate, I no longer take Weinstein seriously as a biologist, or even as an intellectual. He may have been a good teacher at Evergreen State, but he’s not on the rails when it comes to evolutionary biology (his last peer-reviewed paper was in 2005, and Researchgate lists 4 total publications). He’s also advanced specious theories about ivermectin being both a good preventive and cure for Covid, he’s suggested that AIDS was caused by party drugs and not a virus, and he’s suggested that the death of Nobel Laureate Kary Mullis was suspicious, perhaps because Mullis has criticized Anthony Fauci (did Fauci order a hit? LOL!).  Weinstein’s even wrapped his cameras in aluminum foil because he suspected some sinister forces were impeding his transmission. He gave his cameras tinfoil hats!

A tweet from Michael Shermer, aimed at Weinstein, about Kary Mullis’s death:

In his Substack column below, Jesse Singal shows other conspiracy theories/dubious theories that Weinstein and Heying have advanced (Weinstein is more vociferous than Heying, so I give him most of the opprobrium). Click to read:

Here you can see Weinstein going after Dawkins and me by misrepresenting our views. Yes, I do think that understanding of evolution has slowed down since Darwin and since the 1940s, since most of these “founders” seem to have gotten the major parts of the modern synthesis right—except for neutral theory, which was a huge advance. But I surely do not believe (nor do I think that Dawkins believes) that we have pretty much completed our understanding of evolution. But I’ll let Dawkins speak for himself.

And of course the IDers love Weinstein and Heyer’s podcast, because they give so much credit to Intelligent Design in pinpointing the “neglected” Big Questions about evolution.It’s thus a pity that IDers, like Weinstein himself, hardly have any peer-reviewed papers in real scientific journals advancing their theories! Read below to see how much IDers love Weinstein.

 

Now I surely don’t think that Weinstein is stupid at all; he’s really quite smart. But I think that, in his desire to find a niche for himself, and garner a measure of public approbation, he’s deliberately embraced conspiracy theories, highly praised the gussied-up creationism of Intelligent Design, and, most annoying, almost willfully misunderstood evolutionary biology.

The mystery of flatfish evolution: part of it now solved

June 23, 2024 • 10:15 am

Flatfish, in the order Pleuronectiformes, have long been an evolutionary puzzle, for all the fish in this order lie on the substrate—on their sides—with both eyes on one side of their  body, like the flounder below:

By Moondigger – Own work, CC BY-SA 2.5

Phylogenetic analysis shows that flatfish evolved from “regular” fish, fish having one eye on each side and swimming vertically, that evolved over time to lie on their sides. The bizarre thing about this evolution is that it involved genetic changes so that “normal” fish had their eyes move over the top of their head so that both eyes look upwards.  Their skin changes color and texture, too, with the top half colored, as above, and the bottom half pale.

And all flatfish begin their development like “normal fish”, swimming vertically and having one eye on each side of the head. Then, as the fish gets older, one eye migrates over the top of the skull to the other side! (You can see that in the video below.)

When the eyes are both on one side, the flatfish tip onto their sides and spend the rest of their adult life lying on one side. (The side varies among species: some have 100% right-sided individuals, others 100% left-sided, and some species are random, with half of the individuals having the right eye move over (and lying on their right side), and the other half having the left eye move.

Living on the substrate like this, and often camouflaged as the flounder above, is an advantage for the fish, both protecting them from predators and, since they are predatory piscivores (fish eaters), hiding from their prey.

Here’s a video of the development of a young flatfish, showing the eye migration.  Since the ancestor had both eyes on one side, like the young flatfish, this is a case of “ontogeny recapitulating phylogeny”—that is, the development of a single living fish goes through a process mimicking the evolution of their adult ancestors.

But since the weird developmental pathway is presumably an adaptation that evolved by (presumably stepwise) natural selection, two big questions immediately arise:

  1. What were the intermediate evolutionary stages of eye migration?
  2. What were the evolutionary advantages of this migration, which presumably involved a gradual evolutionary movement of the eye from the side to the top of the head, and then over the head to the other side?  It’s hard to see how, for example, an eye that’s halfway around, so it’s close to the top of the skull but hasn’t moved to the other side, could leave more offspring, or survive better, than their ancestors. What would be the advantage of each small step of the migration?

It’s hard to envision a gradual Darwinian process that could produce this migration. As Carl Zimmer wrote in a new NYT article that summarizes recent flatfish findings (click below), Darwin’s critics used both questions about to cast doubt on his theory.  In response, some “saltationists”, who assumed that major evolutionary changes occurred in one huge step rather than a series of gradual steps, said that a single mutation moved the eye from one side to the other. (But that would not be advantageous unless the fish had already evolved to lie on its side!)

Click below to read the Zimmer piece in the NYT here (the drawing is animated), or find it archived here. 

 

As Carl reports, there was another weird finding that now seems doubtful: a 2001 paper by a group of Chinese researchers who, using DNA=based family trees, seemed to show that flatfish evolved twice.  You can see that paper in Nature Genetics by clicking on the headline below, or read the pdf here.  The discovery that flatfish seemed to be “polyphyletic”—with more than one evolutionarily independent origin—was deeply weird, because the hormone-induced eye migration, which is extraordinarily complex, would have had to evolve twice. It’s not impossible, but seemed unlikely. One of the doubters was evolutionist Matt Friedman, who got his Ph.D. here and is now a professor at the University of Michigan and director of its Museum of Paleontology.

A while back, when he was still at Chicago, Friedman published what I see as the most interesting of the three papers highlighted here. This one was in Nature, and you can read it by clicking below or seeing the pdf here

Note that this paper was a lot of work, and yet, unlike the others, Friedman was the sole author. I love to see single-person research efforts like this.  That aside, what Friedman found were two fossil evolutionary intermediates between adult “normal” fishes (the presumed ancestors of flatfish) and modern flatfishes, having both eyes on one side. Friedman reanalyzed a neglected species, Amphistium paradoxum, and a described a new fossil fish, Heteronectes chaneti, both from the lower Eocene, about 50 million years ago.

Amazingly, both species (the former randomly sided and the latter lying on its left side) showed an intermediate placement of the eyes in the adult fish. Both eyes were on the same side of a vertically-oriented fish, but one eye had migrated upwards toward the top of the skull, so that the fish could presumably see both to the side and also, perhaps, a bit above them.  Thus we have two evolutionary intermediates of the adult stage, likely showing that the eye movement did not occur in one big evolutionary leap.

Here’s a photo from the 2008 paper of the left and right sides of the H. chaneti skull, showing the eye sockets, which I’ve circled.  The asymmetry is obvious:

(from the paper): a, Heteronectes chaneti gen. et sp. nov., holotype, NHMW 1974.1639.25 (dextral morph); transfer preparation dusted with ammonium chloride and presented in right-lateral view. b, Counterpart, NHMW 1974.1639.24; transfer preparation dusted with ammonium chloride and presented in left-lateral view, showing migrated orbit.

And a reconstruction of the Amphistium species, showing both sides. The asymmetry is again clear, but the eyes of the adults are still on opposite sides of the head:

(From the paper): b, Reconstruction of Amphistium, showing sinistral (front) and dextral (back) individuals in the left lateral view (modified from ref. 20)

You’ve probably realized that this addresses question #1 above, showing that the movement was presumably gradual over evolutionary time, though we need more fossils to show that it was a continuous series of small steps. But at least the movement didn’t seem to involve one big leap.

But that leaves question #2, which I’ll address in a moment.

The reason Zimmer’s note came out now, though the papers above date from 2008 and 2021, is that a group of authors recently published another DNA based analysis in Nature Genetics showing that the Chinese group was probably wrong: flatfishes and their eye movements seem to have had a single evolutionary origin. (The Chinese group maintains that their “polyphyly” conclusion is still the best one.)

Click below to read, or find the pdf here.

 

Before returning to the Big Unsolved Question, I’ll show the phylogeny advanced in the 2001 paper (bottom), showing two origins of flattening and eye migration, and the newer analysis by Duarte-Ribiero et al.  at the top (Friedman is the third author), showing a single origin of flatfish (I’ve circled it).  This newer paper also singles out some genes that, showing signs of selection in their DNA sequence, may be involved in the evolutionary transformation, but I’ll leave that issue aside.  Green silhouettes are flatfish, black are nonflat fish.

(Part of it from paper): (From paper, and there’s more): a, FM tree estimated using LEA’s dataset with ASTRAL under an NHM (GHOST) of nucleotide substitution (see Supplementary Note 2 for details on time calibration). b, FP tree illustrates the phylogenetic hypothesis and divergence times proposed by LE

Now for the big mystery.  How could there possibly be an evolutionary advantage to each step of the eye movement? Presumably the adult either laid on its side or swam “normally”, and what would be the advantage of intermediate stages when the eye gradually moved up, across the top of the skull, and settling on the other side?  The movement is presumably advantageous only when the fish is already on its side, but then what would be the advantage of moving a few mm towards the top of the skull?

Well, perhaps the fish didn’t lie fully on its side. Here’s one clue in a quote from the 2008 paper:

Questions about the possible selective advantage of incomplete orbital transit arise from the discovery of stem flatfishes. Clues are given by living taxa, which often prop their bodies above the substrate by depressing their dorsal- and anal-fin rays. Similar behaviour might have permitted Amphistium and Heteronectes—both of which have long median-fin rays—the use of both eyes while on the sea floor. The unusual morphology and resting orientation of pleuronectiforms have been interpreted as adaptations for prey ambus, and it is clear that stem flatfishes, like morphologically primitive living forms, were piscivorous; one specimen of Amphistium (MCSNV V.D.91+92) contains the remains of a fish nearly half its own length.

So perhaps this happened: a normal ancestor, through behavioral evolution, adapted to hanging around the sea bottom, as they were less conspicuous and could get more prey.  But they’d have a more difficult time seeing upwards with eyes on both sides of the head. Movements of the eyes toward the top of the skull could be advantageous so long as they occurred in concert with behavioral changes (first perhaps learned, then evolved) involving propping themselves up with their fins. The advantage of tilting a bit would be that the fish might become a bit less conspicuous.

This whole scenario, as I proposed it (and I’m sure others have before in some form) presumes that the eye movement is either induced by or occurs in concert with changes in the fish’s behavior, which initially could have been learned and not coded in the genes. (Ernst Mayr once said something like “all major evolutionary changes begin with a change in behavior”). I don’t know how to test the hypothesis, as even finding more fossils with intermediate stages of eye migration will tell us little about the selective pressures involved. But for sure the movement involved natural selection rather than other evolutionary forces like genetic drift, for we have a big directional change involving many genes, genes that involve both morphology and behavior.

In short, I don’t know how it happened. But seeing that modern fishes can use their fins to prop themselves up on the sea floor may give us a clue. And other scenarios may be possible; readers can entertain themselves by finding alternative ways this change could have occurred by natural selection.

Richard Dawkins interviews John McWhorter on linguistics and “woke racism”

June 9, 2024 • 12:15 pm

Here Richard Dawkins interviews linguist and author John McWhorter, a person familiar to readers of this site. And most of the 54-minute discussion is about linguistics.

It’s refreshing to hear McWhorter’s enthusiasm for linguistics, and this bit of the discussion goes from the start of the interview until about 37 minutes in. It’s sad that McWhorter has, by his own admission, been more or less drummed out of the fraternity of academic linguists because of his heterodox views on racism. I’m sure, based on this interview alone, that he was a terrific teacher.

At any rate, McWhorter explains why he began studying linguistics (it involves Hebrew), how many times he thinks language originated (McWhorter thinks just once, though he’s not convinced that this is supported by the existence of a “universal grammar” or universal “recursion”: subordinate phrases embedded within phrases). Rather, McWhorter is convinced of a single origin of language by parsimony alone. As to when it originated, McWhorter makes rather unconvincing arguments (criticized by Richard) that Homo erectus could use syntactic language; he’s on more solid ground when he thinks that Africans, because of evidence of their mental sophistication, used language around 300,000 years ago.

They discuss evidence that the FOXP2 gene was implicated in origin of language, and McWhorter is accurate in saying that this theory hasn’t worked out, though he believes, along with Steve Pinker, that the ability to use syntactic language is encoded in our genome.

The discussion of “woke racism” (the title of McWhorter’s well known book, which was originally “The Elect”) begins at 36:40.  Dawkins moves the discussion into why McWhorter considers woke racism a “religion”, even though there are no supernatural beings involved. I’m not particularly concerned whether one conceives of progressive racial activism as an ideology or a religion, for it seems a semantic question. To me the more interesting questions are the characteristics of the movement (Does it promote irrationality? Is it disconnected from reality? Does it promote “safe spaces”, which McWhorter sees as a religious concept?)

The discussion moves to the question of why you are considered black (or claim you are black) if you have any black ancestors, which leads to McWhorter’s assertion that we have to go beyond race as a personal identity.

The discussion finishes with McWhorter pushing back on the “defenestration” of figures like Thomas Jefferson because they were either slaveholders or didn’t denigrate slavery. He sees this demonization as “pernicious for education”, although he agrees that some extreme versions of racism (e.g., Woodrow Wilson) warrants taking down statues or erasing names. And what, he muses, will demonize us to our descendants.

It’s a very good discussion, I think, and shows McWhorter’s passion, eloquence, and thoughtfulness.

Since McWhorter mentions Jamaican patois as a form of English that isn’t recognizable as English, I wanted to hear some of it, so I’ve put the video showing such patois below.

h/t: Williams Garcia

Mimicry in butterfly flight behavior

March 15, 2024 • 10:00 am

I’ve discussed many types of mimicry over the years, and one of them is Müllerian mimicry, in which a group of species, often not that related, come to mimic each other in appearance. In this form of mimicry, the different species are all aposematic: that is, they have bright warning coloration and obvious patterns, all evolved to deter predators.  (The form of mimicry is named after the German zoologist Fritz Müller.)

The way it usually works is that a group of species, often butterflies, are subject to predation, but are also unpalatable since they ingest plant compounds that are either toxic or can be converted to toxic ones. (Determination of unpalatability may involve tests with caged birds, observation of what a butterfly eats, or even, in the case of macho biologists, eating the butterfly itself, though human taste may not mimic butterfly taste).

At any rate, each species develops aposematic patterns and colors, which lets the predator know to stay away from the butterfly. This evolves not for the genetic sake of the bird, of course, but for the butterfly, as such coloration and obvious patterns give the aposematic individual a survival advantage over others. (How this occurs, which makes the initial individual conspicuous and perhaps more likely to be caught, is somewhat of a mystery, but there are some hypothesis that have been experimentally supported.)

Once you get some species of butterflies in one area that have warning colors and patterns, natural selection can then act to make their different colors and patterns come to resemble each other. That’s because if a bunch of toxic butterflies look alike, the predator learns to avoid them more readily (it has more chances to learn). Ergo, mutations in individual butterflies of different species that lead to a convergence in their appearance will be favored, reducing the chance of individuals being eaten by birds. This can lead to quite unrelated species of butterflies adopting similar colors and patterns.  (Of course, all the lookalike Müllerian species, which can be quite unrelated—even including both butterflies and day-flying moths—must live in the same area, because this convergent evolution requires reinforcement by predators that can encounter all the mimics.)

Here’s a group of six unrelated butterflies that are part of a Müllerian mimicry ring. Each species is in a different genus! Moreover, there’s a moth species in there, too! Can you spot it? (answer at bottom).  The photo is courtesy of Dr. Mathieu Joron, whose webpage is here, and is used with permission.

From site: The photo shows Müllerian mimicry of various Ithomiinae, a day-flying moth and Heliconius numata from San Martín, Eastern Peru. This sub-ring of the tiger ithomiine mimicry ring occurs commonly between 500 and 1800 m altitude on the Eastern slopes of the Andes from Ecuador to Bolivia. Top row: Hypothyris meterus meterus, Mechanitis mazaeus ssp. Second row: Hyposcada anchiala mendax, Heliconius numata bicoloratus (Nymphalidae: Heliconiiti). Third row: Chetone sp. (Arctiidae: Pericopinae), Melinaea “marsaeus” mothone. All are Nymphalidae: Ithomiinae unless otherwise stated. See also details of other ithomiine — H. numata mimicry rings from San Martín, Mathieu Joron’s web page and the paper by Joron et al. on the maintenance of mimetic polymorphism in Heliconius numata. (photo © Mathieu Joron 2001)

Note that there’s no need for species to be related to each other for this to happen, as the evolution of similar color patterns happens independently in each species, all mediated by visually hunting predators. A single Müllerian mimicry ring can involve true bugs (Hemiptera), wasps, beetles, and butterflies.

And different populations of a single species, if they live in different places that have other species of aposematic butterflies, can evolve different patterns in those different places to look like the local deterrents. Here’s an example of single species (the top four species are all Heliconius numata) that mimic other aposematic species in the genus Melinaea in different areas.  Remember, the top four drawings are all members of the same species, but living in different areas. Further the caption notes, “the bottom four are H. melpomene (left) and H. erato (right), which mimic each other.” Thus in the bottom four we see two cases of Müllerian mimicry.

As you see, things can get quite complicated.

Source:Repeating Patterns of Mimicry. Meyer A, PLoS Biology, Vol. 4/10/2006, e341 doi:10.1371/journal.pbio.0040341l; CC BY 2.5, via Wikimedia Commons

 

Butterflies in the genis Heliconius are particularly famous for showing Müllerian mimicry, and feature largely in a new paper from PNAS. What the authors were studying was not the the patterns and colors of butterflies in Müllerian mimicry rings, but mimicry of their behavior.  It’s easy to see resemblance in color and pattern, but biologists have largely neglected the very real possibility that because predators can see behavior as well as appearance, mimics might evolve to resemble each other in behavior, too.  This is well known in salticid “jumping spiders”, which have evolved to mimic the walking behavior of ants. (Predators hate ants since they sting and often taste bad as well.) There’s a video of an ant-mimicking salticid at the bottom.

In this paper the author studied 29 species of heliconiine butterflies and 9 ithomiine species, belonging in total to 10 mimicry rings. They wanted to see if there was, in each mimicry ring, an evolution of similar “flight behavior”, because predators can see not only how a butterfly looks, but, when it’s on the wing, how it flies. They found that there was indeed evidence in each Müllerian mimicry ring that the species had evolved similar flight behaviors. Clearly, natural selection had altered flight behaviors within a ring to make the species flap more like the other ones, with the explanation being that predators learn to avoid not only certain color patterns, but also certain ways of flying.

(Note: I am imputing bird avoidance to their learning which species are toxic, but there’s no reason why birds cannot undergo genetic evolution via selection to innately avoid certain colors and behaviors since individuals with genes tending to cause such avoidance will be favored. (This is presumably because getting sick after a meal is something that natural selection would eliminate by favoring gene forms that instinctively avoid certain appearances and behaviors.)

Read the paper by clicking on the title, or see the pdf here.

I will be brief since the analysis is complicated, involving all kinds of corrections for wing size, relatedness, habitat, and other factors; and I’ll just give the conclusions.

For several members of each species, the authors used cameras to measure three aspects of flight:

  1. Flapping rate of the wings
  2. “Up angle” (the angle between the wings of an individual at the top of its upstroke)
  3. “Down angle” (likewise, but with the angle measured at the bottom of the downstroke)

And, lo and behold, when you correct for relatedness, wing size, ecological area, and other factors, the authors still found significant similarity between members of each of the ten mimicry rings they measured. This held, though, only for the first two parameters: flapping rate and up angle. There was little convergence among members in down angle, for reasons that aren’t clear (perhaps birds can’t see it as well. Here’s the authors’ tentative  ad hoc explanation:

. . . down wing angles respond differently to selection exerted by predators and may be indicative of greater aerodynamic constraint on this trait. Fuller characterization of flight may provide stronger evidence of whether different components of flight are evolving under different selection pressures.

Here’s a figure from the paper showing the ten Müllerian mimicry rings they studied, each ring indicated by a different color. The groups’ conventional names are given by the key at upper left. The “tiger group” is the most famous.

(From paper): Diversity and convergence of wing patterns among the heliconiine and ithomiine taxa whose flight patterns have been measured. Background color indicates the 10 mimicry groups. Transparent (Ithomiine) 1: Ithomia salapia travella, 2: G. zavaleta; Tiger (Ithomiine) 3: Melinaea marseus phasiana, 4: Tithorea harmonia, 5: Mechanitis polymnia, 6: Melinaea menophilus zaneka, 7: Mechanitis messenoides deceptus, 8: Melinaea mothone mothone, 9: Hypothyris anastasia honesta; Tiger (Heliconiine) 10: Heliconius ismenius bouletti, 11: H. p. butleri, 12: Heliconius hecale felix, 13: Eueides isabella nicaraguensis, 14: H. pardalinus sergestus, 15: Heliconius numata bicoloratus, 16: Heliconius numata aurora, 17: Heliconius ethilla aerotome; hewitsonii-pachinus 18: H. pachinus, 19: Heliconius hewitsoni; cydno–sapho 20: Heliconius cydno chioneus, 21: Heliconus sapho sapho; Blue 22: Heliconius doris viridis blue, 23: Heliconius wallacei flavascens, 24: Heliconius leucadia pseudorhea, 25: Heliconius sara sara, Postman 26: Heliconius timareta thelxinoe, 27: Heliconius melpomene rosina, 28: H. e. favorinus, 29: Heliconius erato demophoon, 30: Heliconius melpomene amaryllis; Orange 31: Eueides lybia olympia, 32: Eueides aliphera aliphera, 33: Dione juno juno, 34: Dryadula phaetusa, 35: D. iulia; Dennis rayed 36: Heliconius elevatus pseudocupideneus, 37: Heliconius burneyi huebneri, 38: Heliconius aoede cupidensis, 39: Heliconius melpomene aglaope, 40: Heliconius doris viridis, 41: Heliconius eratosignis, 42: Heliconius demeter joroni, 43: H. e. emma; Red and white 44: H. himera; Zebra 45: H. charithonia. Butterflies images are from the Neukirchen Collection, McGuire Centre, Florida; https://www.butterfliesofamerica.com/ (Andrew Warren); http://www.sangay.eu/esdex.php/ (Jean-Claude Petit).

But it gets even nicer, for the authors also looked at flight similarity between isolated populations of the same species that were members of different mimicry rings, which, as I said above, can happen They used populations of two species, Heliconius melpomene and H. erato. Again, different populations of each species appear to have evolved similar flapping rates and up angles (but not down angles) to species of the different mimicry rings they’ve joined.

The ages of these conspecific populations can be estimated from molecular data as less than half a million years, so the flight mimicry can evolve quite rapidly. As for the other species, well, some of them are not that related, being separated by up to 70 million years from their common ancestor.

The upshot: Müllerian mimicry is often thought of as visual phenomenon because it’s mediated by visually hunting predators.  And it is, but the emphasis on vision has led biologists to concentrate on easily-discerned colors and patterns (birds have color vision). Yet vision can also detect behaviors—in this case flight behavior. This isn’t really a brand-new discovery, because mimetic behavior has clearly evolved in other cases. As I said, we see Batesian mimicry in which salticid spiders, which are edible, have evolved to walk like ants that are avoided by predators (see below).  But the important lesson of this paper is that biologists studying visual mimicry should not neglect to look at behavior of animals and not just their appearance.

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

To end, here’s a remarkable case in which an edible jumping spider has evolved to not only look very similar to weaver ants, which are avoided by predators, but also to walk like ants.  This is a case of Batesian rather than Müllerian mimicry, but it does show mimetic evolution of behavior.

 

Answer to question above: Which species is the moth in the first picture above? It’s Chetone sp.! (Bottom left.)