Category: evolution

A remarkable case of pollinator/orchid coevolution and specificity

September 29, 2023 • 9:45 am

A science paper at last! Truth be told, I don’t come across many science papers that are both of general interest and that I can explain easily. But I do have several more in the queue.

A colleague sent me an old paper (from 2006), but its age does not diminish how spectacular the results are. And in short, the results are these: a group of 15 phenotypically similar (but probably not closely related) orchids in SW South Africa are pollinated by females of a single species of bee, which collects oil produced by the flowers and feeds it to their offspring.

This poses a problem, because orchids are pollinated by affixing sticky pollinia (sacs of pollen) collected from a flower of one species to the next flower of the same species. (The orchids in this group do not self-fertilize). With pollen sacs from 15 different orchid species sticking to a bee, how can a plant be sure that its own pollen gets transferred to another individual of the same species, rather than to another individual of a different species, in which case cross-species pollination would produce either inviable or maladapted hybrids?

The bees and orchids have solved this in a very clever way.

But let’s back up: the paper, from the American Journal of Botany, can be seen for free by clicking on the screenshot below, and the pdf is here.

The reason the author, Anton Pauw, gives for his 8-year investigation is that, he says, the “conventional wisdom” in botany is that it’s not adaptive for a bunch of flowers to depend on a single species of pollinator. That’s because if some environmental fluctuation or other contingency makes the pollinator rare (or even drives it extinct), the flowers wouldn’t get pollinated. This would imply that flowers should evolve to attract several species of pollinator, for those flowers that are generalists in this way are less likely to become rare or extinct themselves.

But this doesn’t seem to be the case in this group of 15 orchids, which, according to Pauw’s observation, come from three different genera (molecular phylogeny also suggests that they’re not each other’s closest relatives, though they look remarkably similar). Yet all are pollinated by a single bee, Rediviva peringueyi. This is in a genus called “long-legged oil bees.”

The flowers, as I said, look like each other, all produce oil that the bee collects, and all live in the same area, as well as flowering at the same time. As the author says,

Subgroups of similar plant species can be recognized within the extensive oil-bee pollination system. The one examined here includes 15 oil-secreting orchids that share the following syndrome of floral features: pale yellow-green flowers without extensive black markings; secretion of floral oil as a pollinator reward; characteristic pungent scent; flowering period 15 August to 25 October peaking in September; flower depth 5–8 mm (Fig. 1a–n). The species occur in close association with one another in the lowlands of the Cape Floral Region and include members of three genera (Pterygodium, Corycium, and Disperis). According to the pollination syndrome concept, the similar floral features of this group indicate a shared pollinator. My aim was to test this prediction through extensive field work.

Figure 1 below (click to enlarge; caption from paper) shows how similar the flowers are. The pollinating bee (R. poeringueyi, which I’ll henceforth call “the bee”) is shown in the middle. The arrows show where the pollinia of each orchid species gets attached:

Figure 1. The Rediviva peringueyi pollination guild. Center, the oil-collecting bee R. peringueyi, arrows indicate pollinarium attachment sites of orchid species. (a) Pterygodium catholicum. (b) P. alatum. (c) P. caffrum. (d) P. volucris. (e) Corycium orobanchoides. (f) Disperis bolusiana subsp. bolusiana. (g) D. villosa. (h) D. cucullata. (i) D. circumflexa subsp. circumflexa. (j) P. inversum. (k) P. hallii. (l) P. platypetalum. (m) D. ×duckittiae. (n) P. cruciferum. (o) D. capensis var. capensis. Attachment sites f–i after Steiner. Pollinarium attachment sites are confirmed in a–g. Pollination and/or pollinarium attachment are predicted in h–o on the basis of floral features. R. peringueyi 5× life size, orchids 2× life size. Images e, h, k by Bill Liltved.

The bees also collect pollen and nectar, too, but not from these orchids.  From these 15 orchids they take only flower oil (I had no idea it even existed), and do so by, as you can see in the photo below, gripping the plant with the bee’s middle and hindlegs and collecting the oil with modified forelegs. In the process (and of course this is why the flower produces oil and scent to attract the bee). During oil collection, the pollinia of the orchid, which is sticky, attaches to the bee’s body. That’s also shown in the photo below.

This, of course, raises the problem noted above. If a pollen sac from one of the 15 orchid species is stuck to the bee’s body, how can it be guaranteed to pollinate the same species of orchid, for there’s no guarantee that the next flower the bee visits will be from the same species. (All the orchids are, after all, flowering at the same time.)

The answer is the cool part of the story. Each orchid has evolved to stick its pollen to a different part of the bee’s body. And each orchid has its female parts placed so that the pollinia from its own species, stuck to a specific place on the bee’s body, will contact it’s own species-specific style (the female bit that gets the pollen for fertilization). Thus cross-pollination is prevented by the specificity of where the pollinia stick to the bee and bu the specific position of the female part of each orchid, which has evolved so, that when the bee collects oil, the right pollen will land on the right stigma.

Paux found this out by identifying the different pollina of the flowers (they have different shapes), and trapping wild bees to see where the pollinia of each species was stuck to the body. That’s what’s shown in the figure above: each letter corresponds to the orchids depicted around the edges, and the arrows show where on the bee’s body the pollinia from each species are stuck. Notice that they’re all different. Except for two, that is: the pollinia from orchids b and c, which both stick to the foretarsi of the bee’s middle legs.

Does this mean there’s cross-pollination between orchids b and c, which would be bad? No, because the pollinia of these two species are of different length, and the stigmas of the two orchids are placed so that each will get the pollen from the right species.

This is a remarkable example of specificity in pollen placement; I know of nothing similar! You can see below, in “b” and “c” of Fig. 3, that the pollen are stuck to very specific parts of the body. In “b”, the pollen of the flower Pterogodium cathlocium get attached to the bee’s “basistarsi” on the middle legs (the most distal part of the large leg tarsi), while the pollinia of the orchid Pterygodium volucris get attached to the ventral surface of the bee’s abdomen. The pollen sacs on the flowers have to be in very different places to accomplish this, and the bee has to collect oil in a specific position to get the pollinia stuck to the right spot.

(From paper): Fig. 3. Rediviva peringueyi pollination mechanism. (a) Female R. peringueyi collecting floral oil from the apex of the lip appendage of Pterygodium alatum with a rapid rubbing motion of the front tarsi. The bee hangs onto the lip appendage with the middle tarsi, onto which the pollinaria (visible) become attached. Bar: 3 mm. (b) Several pollinaria of P. catholicum attached precisely to the basitarsi of the middle legs of R. peringueyivia the sticky viscidia. Bar: 1 mm. (c) Pollinaria of Pterygodium volucris attached to the ventral surface of the last abdominal segment of R. peringueyi. Bar: 3 mm.

Note that several types of evolution appear to be involved in this phenomenon:

a.) Convergent evolution of the different, unrelated orchids so that they develop a common scent, appearance, and “lip” that allows the bees to hang on while collecting oil.

b.) Divergent evolution of the orchids so that each evolves a lip and pollinia position that will stick its pollen to a previously uncolonized part of the bee’s body

c.) Possible evolution of the bee’s behavior so that it “knows” how to hold onto each species of flower to collect oil (this might not involve genetic evolution, but simply be due to learning).

So this is the cool way that fifteen different species of orchids can pollinate members of their own species, even if they’re all serviced by the same species of pollinator.  According to Pauw, though, this doesn’t solve the problem raised at the beginning: such specificity makes the whole system precarious—liable to collapse if anything happens to the pollinator. And indeed, he says that the degree of pollination of the orchid species vary strongly from year to year. So it goes.

Another aspect of this system is the possible extinction of the bee. In a sad ending, Pauw notes that the habitat for both orchid and bee is disappearing:

The biggest challenge in this study was the scarcity of suitable study sites. About 80% of lowland vegetation has already been transformed by urbanization and agriculture (Heijnis et al., 1999). What remains are scattered fragments of natural habitat, mostly less than 1 ha in size. In many of these fragments, the absence of R. peringueyi and repeated pollination failure in the entire guild was recorded. We have probably already lost the chance to understand the intriguing flowers of species such as P. cruciferum, which persists in fewer than five remnants of natural vegetation where they seldom, if ever, receive pollinator visits. In contrast with the pollination systems of the north temperate regions, which almost invariably involve several ecologically equivalent pollinator species (Waser et al., 1996; Fenster et al., 2004), the pollination system described here is dependent on a single insect species. This presents a challenge for conservation because of the low level of ecological redundancy means that the loss of R. peringueyi may trigger linked extinctions amongst the plants in the R. peringueyi pollination guild. It seems unlikely that the R. peringueyi pollination guild will persist in a modern, cultural landscape without unique conservation planning.

If the bee goes extinct, so will every one of these orchid species, for their reproduction depends on the insects. There’s a lot more to study here, and I’m hoping that they’re trying to save some habitat for both plant and insect.  Since pollination itself has been observed in only about five of these orchids, there’s a lot more observational work to be done. Further, the DNA analysis of the orchids, indicating that they are not a “monophyletic group” (i.e., not each other’s closest relatives) was rather crude, and that needs to be done using more modern methods. If they are not each other’s closest relatives, then we have a new and solid case of “convergent evolution” (unrelated species developing very similar traits).

h/t: Martim

Peter Boghossian interviews Luana Maroja (and a note on “transracialism”)

August 22, 2023 • 9:30 am

When my colleague, coauthor, and conspirator in crime Luana Maroja, a professor of evolutionary biology at Williams College, was teaching a short summer course at The University of Austin, she was interviewed on video about sex and gender issues by Peter Boghossian, also teaching at the U of A.

The interview, below, speaks for itself: Luana did a superb job clarifying the biological controversies about sex and gender (and Peter asked some great questions to draw her out).  As you can see, she’s spirited, eloquent, and amiable, with the latter trait helping her convey antiwoke truths without being seen as “strident”. She’s a great collaborator. The interview is well worth listening to, and I don’t say that because Luana and Peter are friends of mine.

Here are the YouTube notes:

Luana S. Maroja is a renowned evolutionary biologist, Professor of Biology, and Chair of the Biochemistry & Molecular Biology Program at Williams College. She was taken aback when the Society for the Study of Evolution released a statement promoting sex as a spectrum and declaring the validity of “lived experience” in sexual identity. What would inspire such a misguided, conspicuously anti-scientific declaration? In this conversation with Peter, she answers that question.

In plain language, Luana explains chromosomal differences in mammals and how the sex binary is expressed in animals. She addresses popular arguments about exceptions to the binary, such as variations in sex chromosomes, hormone receptor failure, and developmental sex disorders.

They also discuss: Moralistic and naturalist fallacies, bimodality, being “born in the wrong body,” social constructs, clown fish, non-biologists teaching bad biology, and trans racialism.

Luana S. Maroja earned her undergraduate and master’s degree from the Federal University of Rio de Janeiro and her PhD from Cornell University. Her research interests include population ecology, speciation, population genetics, phylogeny, and phylogeography. Luana studies a variety of organisms, including small mammals, insects, and plants, and has published more than 35 scientific papers.

Luana co-authored The Ideological Subversion of Biology, the cover article in the July/August 2023 issue of Skeptical Inquirer magazine.

Chapters

0:00 Intro

6:30 Biological view of gender vs sex

12:40 Can you change sex?

15:23 Gender binary

23:55 Reality denialism

28:00 Reaction to SSE videos

38:13 Biological differences in behavior & expression

43:10 Transitioning/Wrap up

I want to make one point about “transitioning” at the very end, where hey discuss why for the woke it’s not only fine but admirable to transition genders, but not okay to transition races (“transracialism”). The philosophical basis of these two transitions was discussed by philosopher Rebecca Tuvel in a 2017 issue of Hypatia, and caused a big controversy after Tuvel concluded this in the abstract (my bolding):

Former NAACP chapter head Rachel Dolezal’s attempted transition from the white to the black race occasioned heated controversy. Her story gained notoriety at the same time that Caitlyn Jenner1 graced the cover of Vanity Fair, signaling a growing acceptance of transgender identity. Yet criticisms of Dolezal for misrepresenting her birth race indicate a widespread social perception that it is neither possible nor acceptable to change one’s race in the way it might be to change one’s sex. Considerations that support transgenderism seem to apply equally to transracialism. Although Dolezal herself may or may not represent a genuine case of a transracial person, her story and the public reaction to it serve helpful illustrative purposes.

and in the conclusions:

I hope to have shown that, insofar as similar arguments that render transgenderism acceptable extend to transracialism, we have reason to allow racial self-identification, coupled with racial social treatment, to play a greater role in the determination of race than has previously been recognized. I conclude that society should accept such an individual’s decision to change race the same way it should accept an individual’s decision to change sex.

Wikipedia describes the blowback from what I think was Tuvel’s a reasonable conclusion. The fracas included a groveling apology by the journal and the resignation of eight editors. Yet I still don’t see any fundamental philosophical difference between a white person claiming that they have a black identity because they “feel black” and a male claiming that they have a female identity because they “feel like a woman.”

On the other hand, the video above inspired some discussion on the Heterodox STEM site about the transracialism vs. transgenderism issue, and some people perceived a meaningful difference from a woke point of view.ˆ That difference is this: transgenderism is supposedly seen by the woke as turning one into a victim or a member of a protected class: it is a disadvantage. (Although transgender women participating in women’s athletics do accrue an advantage, this is largely denied by the woke.)

In contrast, some (but by no means all) forms of transracialism can confer advantages to people—advantages that are seen by the woke as unfair. The discussion centered on white people like Rachel Dolezal who say they are black because they feel black (she also modified her appearance so she could pass as a black person).  By passing as black if you’re not, several people argued that you would accrue an unfair “affirmative-action-based” advantage in things like college admissions and getting jobs.  Other forms of transracialism could also give one advantages: we’re familiar with Elizabeth Warren claiming she had Native American ancestry, a claim that she thought would give her credibility as a member of an oppressed minority. And there’s the book below by an Indian-American who couldn’t get into medical school because of poor grades until he decided to say he was black, and was immediately accepted by many schools. (He later dropped out.) Click to see the Amazon link:

Two points here. First, not all whites who pass as black will get advantages. I’m not sure how much Dolezal benefited personally from pretending she was black, though she did become president of the Spokane branch of NAACP.  On average, a black person is worse off than a white person in terms of prospects, education, income, and so on. Thus you gain the advantage of white—>black transracialism only if you’re assuming the identity of an “elite” black person, like someone in a position to apply to graduate school. And other forms of transracialism, including blacks assuming the identity of Asians or vice versa, wouldn’t get you these advantages because the assumed identity is not credible on a physical basis (though physical appearance shouldn’t matter).

Thus you could justify a difference between transracialism and transgenderism only if you’re woke, and it’s a practical rather than a philosophical difference.  Transracialism isn’t okay because some forms of it give one an unfair advantage via forms of affirmative action, while transgenderism is always okay because it puts one into a protected class that is said to be oppressed.

That’s one way the two forms of “trans” identity can be differentiated, but only by woke people, and only using practicality and ideology rather than philosophy.  Philosophically, I still agree with Tuvel that there’s no substantive difference between assuming a different gender or assuming a different race.

Revisiting an old paper

July 20, 2023 • 11:15 am

I was just reminded that in 2020 Hari Sridhar interviewed me about what is perhaps my most cited paper (1561 times to date, though my book Speciation with Allen Orr was cited almost six times as often), and certainly one of the few good ideas I’ve had in my life (the paper was also co-written with Orr). You can see the paper by clicking below, and there was a followup paper in 1997 with the word “revisited” tacked on the title below; that was written since new genetic-distance data had appeared.

Here’s the good idea as it came out in the interview:

HS: You were interested in Drosophila and the genetics of Drosophila right from the time of your PhD. What was the motivation for this particular piece of work?

Jerry Coyne: Well, the motivation is implicit in the paper. I was interested in the genetic basis of reproductive isolation in Drosophila. I realized that there were a lot of data out there on the genetic distances between different closely-related species of flies as measured by electrophoresis, and from reading a lot of the old literature – Patterson & Stone (1949, Univ. Texas Publ. 4920: 7-17), and The Genetics and Biology of Drosophila book series ‑that there is an immense amount of data on the crossability of flies, their sexual isolation, the sterility and viability of hybrids. And it came to me one day in Maryland – I can still remember this – that you could combine that different data using electrophoresis as the estimate of divergence time, and then the other parameters as estimates of the degree of reproductive isolation. By doing that, you could get some kind of estimate of the time course over which reproductive isolation evolves. After that, it was just a matter of compiling that data. It took a long time because it’s all in different places – papers, books and stuff. Nobody had thought to put them together before. It was just a matter of compiling the electrophoretic data with the crossability data and then seeing what came out of that. That was the motivation.

one more Q&A:

HS: At the time when you did this work, did you anticipate, at all, the kind of impact it would have on the field? Do you have a sense of what it mostly gets cited for?

JC: Yeah, it gets cited for the reason that we wrote it, actually. Well, two things. First, It gives an idea of the time course of speciation. But also, the result showing that sympatric species get reproductively isolated much more quickly, in terms of pre-zygotic isolation, than allopatric species, was unanticipated. It supports the idea that there’s either reinforcement or reproductive character displacement. I just said, well, let’s look at these data. Then we went back to all the original papers and looked at the ranges to see whether the species lived in sympatry or not. That was a lot of work too because, a lot of the time, range data is not presented as ranges.You have to look at where the flies were captured and, sort of, get an idea of whether the ranges overlapped or not. Those two aspects of the paper were important. Remember, the paper is incomplete because it leaves out a number of forms of reproductive isolation that could be very important in nature, like post-mating pre-zygotic isolation, sperm competition, ecological isolation and temporal isolation. Those aren’t included, because there’s no data. But the support for reinforcement that we showed, the high degree of pre-mating isolation between sympatric species as opposed to allopatric pairs, stimulated, stimulated, I think, work on reinforcement. Even in my own laboratory, my student, Daniel Matute, worked on reinforcement, I think, partly because of the data from this original paper. So it had a number of influences on the field. I don’t know how important it is. It’s a novel approach. It’s one that you can’t really us with most species because of the lack of crossability data. There have been a few other studies. Leonie Moyle did a similar study in tomatoes, I think, and Tamra Mendelson did a study on darters collecting information on genetic distance. The problem with darters and all other groups is that you just don’t have the ability to do laboratory crosses that you have in Drosophila. So Tammie was limited to about 12-13 species.

I’m sorry to say that I haven’t kept up diligently with other folks’ followup work, as there are more papers building on this one (e.g. here, here, and here). In general, I think, they’ve supported our main conclusions, especially the cool one that sexual isolation (mate discrimination) appears to evolve more quickly between groups that experience some period of “sympatry” (living in the same area) after speciation has begun. That in turn supports the idea of “reinforcement”: that if there is a reproductive penalty to hybridizing (e.g. producing hybrids that are sterile or weak), natural selection will build up mate discrimination so that the production of hybrids is less likely. (The idea is that you leave more of your genes to future generations when you produce healthy, conspecific hybrids, so any gene that favors mating with your own species will be favored.) And indeed, we found a strong pattern of heightened sexual isolation among species that are sympatric rather than allopatric (“geographically isolated”).

I liked the original idea of using genetic-distance data to figure out the time course of speciation (or rather, aspects of speciation: mate discrimination and hybrid sterility/inviability) because speciation is often very slow and reconstructing the process (and seeing if there are any generalizations to be made) can be done only by using proxies of divergence time, which in our case was the “genetic distance” calculated using gel electrophoresis. As I note in the interview, gel electrophoresis is pretty much dead, and DNA sequencing of fly species is the way to go.

Is evolutionary biology racist?

July 19, 2023 • 10:30 am

The first article below is from a creationist website, Creation Evolution Headlines, and its author is a young-earth creationist. Oddly, though, its own headline and its discussion isn’t too far from what some “progressive” evolutionists maintain: evolutionary biology is racist, which explains the paucity of minorities in the field. The first paper, then, is not that different in its theses from the second and third papers below, although both were published in academic journa, Social Psychology in Education and in Evolution: Education and Outreach; and both papers include at least one evolutionary biologist as an author.  Click headlines to read any of them.

(The pdf for the article below can be found here.

In both papers religion is mentioned: African Americans are more religious than whites, and that makes them resistant to studying evolution. This may well be true, but I don’t know what to do about it. Here’s one anecdote I’ve told before. I was invited to lecture on evolution to a black “magnet school” (a high school) on Chicago’s South Side.  At the end of my talk, a girl stood up and asked me if I was saying that Noah’s Flood and (as I recall) the Garden of Eden didn’t really exist. I had to tell the truth and say, “Yes, that’s what I think.” It caused a ruckus, and I could clearly see that the students became resistant to my message. (After the talk, the principal took me aside and said I really should have mentioned all the innovations that Africans had made, like inventing the airplane.)

But here’s from the paper:

In contrast to scientists, African Americans are significantly more religious than most every other American ethnic group. They also overwhelmingly self-identify as Protestant Christians. Thus, African Americans may be more likely than Whites to experience a major dissatisfaction with their pro-evolution courses and faculty. This perception could well affect their feelings about evolution classes and professors. In effect, African-American undergraduates appear to be more aware than Whites of the foundation of evolutionary theory which is

methodological (and de facto metaphysical) naturalism. Their religious inclinations will therefore be in conflict with the culture within the [evolutionary] community and it will be difficult for them to feel a sense of belonging in that community. The same with their moral objections to evolution, moral objections that are well founded in the African-American experience. The demands of methodological naturalism thus become an impediment to the greater participation of people of color in ecology and evolutionary biology.

Evidence exists that religiosity functions as a challenge to inclusion within evolutionary biology. Religiosity is negatively associated with exposure to evolutionary theory, knowledge about evolution, and acceptance of evolution. In a sample of African-American college students, Bailey found that the more religious the students were, the less knowledge they had about evolution. Moreover, religiosity is also associated with having moral objections to the theory of evolution. Thus, a cultural mismatch exists between the religious beliefs of students, and those of evolutionary faculty who are unable to properly deal with religious differences and moral objections to evolution. This  may create a challenge that leads to a lower sense of belonging in fields of study that are entrenched in evolutionary thinking.

But if it’s “methodological naturalism” that religious people object to, they should object not just to evolutionary biology, but to ALL science. For “methodological naturalism” is simply the proposition that the laws of the universe are all that occurs in the sciences: there is no divine intervention.  (This, by the way, is not an a priori decision of scientists to exclude God, it’s a method used because invoking God to explain natural phenomena never gets us anywhere. You all know the story of Laplace and Napoleon: “I had no need of that hypothesis”. Nor do we need The God Hypothesis now; it’s only an impediment to understanding.)

It’s not just evolutionary theory that’s founded on methodological naturalism, but all of science.  If metaphysical naturalism makes you uncomfortable, then you have no business doing science at all.

More problematic is religiosity, since for some believers evolution poses no problem for their faith, but for others it’s an insuperable problem. Yet most Americans reject the naturalistic view of evolution: in fact, a 2019 Gallup poll (data below), a poll taken every few years, shows, that 40% Americans are young-earth creationists, another 33% are theistic evolutions (who believe that God helped evolution along, especially creating humans), while a mere 22%—a bit more than 1 in 5 of us, accept the naturalistic view of evolution as we teach it in college.

73% of Americans, then, think that God had some hand in evolution. That’s nearly 4 out of 5, and those objections are obviously religious ones. The biggest impediment to accepting evolution, as I wrote about in my Presidential paper in the journal Evolution, is religion. (As you can imagine, I had trouble getting this palpably true thesis published.)  I know of no anti-evolution organization that is, at bottom, not based on religion, and there’s a negative correlation among U.S. states and among countries in the world between religiosity and acceptance of evolution.

With respect to minorities in particular, the “solution” that Bergman offers to the inequities in evolutionary biology is for us to learn to talk about religion and evolution:

O’Brien et al. [JAC: the paper below] concluded that

cultural differences in religiosity as well as the moral objections to evolution cannot be ignored in efforts to increase URM’s sense of belonging in EEB educational contexts (or other science fields that are rooted in evolution). A large proportion of the U.S. population is religious and disbelieves in evolution. African Americans and Latinos/as are more religious than the U.S. population as a whole and scientists in particular (Pew Research 2009a, b). One method to improve religious students’ feelings of belonging in EEB contexts might be teach EEB faculty to navigate conversations around religion.

Based on the studies below, and experiences of my colleagues, yes, black students or URMs (underrepresented minorities) are more wary of taking evolution classes because of their greater faith. What do do about that?  Well, I have talked to students who had religious objections to evolution, but only in my office, not in class. And really, one has to be a therapist to deal with this issue. I can tell the students that many people find evolution compatible with their faith but, as you see from the figure above, most don’t. And if they ask me my own opinion, I will tell them that I don’t think religion is compatible with evolution, but, fortunately, I rarely got asked that by students.

Finally, the issue of eugenics comes up, as it does even in scientific societies. The mantra goes that evolutionary biology was founded on eugenics (no, it wasn’t), and that the discipline is still deeply imbued with eugenics (no, it isn’t). True, there was a period about ninety years ago when some evolutionists proposed eugenic schemes, but these schemes were not adopted wholesale by governments (and not at all in the UK), and those countries who did adopt them weren’t hugely influenced by evolutionary biology (if you want to blame any field for eugenics, blame genetics, but that’s hyperbole as well).

The quote below, reproduced in the paper above3 comes from the paper of Joseph Graves, Jr. (below):

During the same period in which African Americans were fighting for a legal end to Jim Crow, evolutionary biology became a coherent disciple. This occurred between 1936 and 1947 (Mayr 1982), with the founding of the Society for the Study of Evolution (SSE) occurring in 1946 (Smocovitis 1994). This was right after the end of WWII in which racial theories had been utilized to justify the slaughter of millions of people in both the European and Pacific theaters of the war. What is not as well realized is that these theories had their origin in the West and prominent evolutionary biologists and geneticists contributed to their rise (Graves 2005a).

First of all, evolutionary biology is not the sole source of bigotry (although in the past it has buttressed it), and the claim that evolution had something to do with the mass slaughters of WWII is either gross hyperbole or wrong. In every war, each side dehumanizes the enemy, and that began well before 1859.  The slaughter of Americans by the Japanese and vice versa had nothing to do with evolutionary biology. Nor did the mass slaughters of Russians by Germans and vice versa, as well as Hitler’s Holocaust. And if you think evolutionary biology led to the Holocaust, read my colleague Robert Richards’ paper, “Was Hitler a Darwinian?“, free online. The answer is a firm “No!”

To blame past eugenics, or to bring up the Tuskegee experiment (a horrible and unethical study, though not an outgrowth of evolutionary biology) for racial inequities in evolution doesn’t comport with with any data I know of, nor with my own experimence. Has a single student ever said that if evolution had been involved with eugenics in the past, they’d be busy studying evolution now, sometimes with the goal of becoming an evolutionary biologist?

Click below to read the O’Brien et al. paper, and you can find the pdf here;

One of the factors these authors invoke as inhibiting minority participation in evolution is religiosity, and I’ll quote from this paper again:

Thus, challenges to inclusion that are likely the results of access to resources (e.g., knowledge, feeling comfortable outdoors) and challenges that are likely the result of real or perceived cultural mismatches between students and EEB faculty (e.g., religion) were both related to feelings of belonging. Moreover, the relationship between challenges to inclusion and sense of belonging remained after statistically controlling for ethnicity.

In addition, cultural differences in religiosity as well as the moral objections to evolution cannot be ignored in efforts to increase URM’s sense of belonging in EEB educational contexts (or other science fields that are rooted in evolution). A large proportion of the U.S. population is religious and disbelieves in evolution. African-Americans and Latinos/as are more religious than the U.S. population as a whole and scientists in particular (Pew Research 2009a, b). One method to improve religious students’ feelings of belonging in EEB contexts might be teach EEB faculty to navigate conversations around religion (e.g., Graves 2019).

Feelings of belonging are a hard one, for one has to figure out how to rectify that. Mentors would help, though, as Graves points out below, there are very few black evolutionary biologists. If you need a mentor of your own race to succeed, there are two ways to fix that. First, departments could practice affirmative action in hiring faculty (we’re doing that as hard as we can given the restrictions on the practice, though it’s now become illegal). The reason it hasn’t worked that well is that there aren’t many minority evolutionary biologists looking for jobs. (One reason, I think, it that it’s not a very lucrative field, but that’s just my take). The underqualification in STEM that leads to this inequity has only one fix that’s permanent: provide people with equal opportunity from birth.  (There are other fixes that aren’t as good, like expanding outreach, and I’m in favor of them, but in the end the problem we need to solve is one that starts at birth, and there is precious little money or will to fix that.) The ultimate goal to me is equal opportunity, not equal outcomes, but the former is a lot harder to ensure.  And of course given cultural differences and preferences, equal opportunity need not lead to equal outcomes.

Finally, Joseph Graves, an African American evolutionist, weighs in with this paper (click to read, pdf here).

His thesis is that current racism (i.e., ongoing “structural racism”) is what keeps minorities out of evolution.

The central premise of this commentary is that racism in America as it is manifested in higher education (specifically evolutionary biology) creates a culturally non-inclusive environment that systematically disadvantages persons of non-European descent. The form of this disadvantage differs by the sociocultural positioning of individuals. Thus to change the patterns of underrepresentation within the discipline requires that the dominant social group (persons of European descent socially-defined as “white”) to address and act on how their position of privilege is subordinating “others.”

I’d agree with him insofar as the qualifications of minority scientists were eroded by the history of slavery and racism, but I can’t agree that racism is pervasive in evolutionary biology right now. There are simply too many efforts to find and recruit minority and faculty students to support the view that the field is riddled with systemic racism.

And then there’s religion, with Graves indicting my own views:

Darwin’s agnosticism on the existence of God is a well-known feature of his life (Desmond and Moore 1991). Jerry Coyne’s position on the incompatibility of evolution and religion is one that I shared earlier in my career (Coyne 2012). However I have since recanted. Such views certainly stand as an impediment to the successful recruitment of greater numbers of African American students to careers in evolutionary biology.

I question whether my position or views like mine have kept students out of evolutionary biology. Can you find one student who says, “I would have become an evolutionary biologist, but Jerry Coyne convinced me that science and religion are incompatible, so I didn’t major in science or take an evolution course”?  I doubt there are more than a handful of students in America who have even read Faith Versus Fact: Why Science and Religion Are Incompatible.” The recruitment of minority students into evolution may be because of religious belief that’s hard to overcome, but I doubt it’s because of the argument I made. That argument was not that religious people couldn’t accept evolution, or that scientists couldn’t be religious. Rather, it was that if you practice both science and religion, you are engaged in contradictory exercises: both fields are based on factual claims (religion, of course, is based on more than that), but only science has a way of determining whether those factual claims are true. This is a more sophisticated argument than simply saying, “Evolution makes a hash out of Christianity.”

I’m not denying, though, that religion is an impediment for black students to enter evolutionary biology; I have had colleagues teaching at various schools who told me they were explicitly told this by minority students. Graves, however, thinks it can be overcome with complex discussion:

However, this [religious belief] need not stand as impediment to the recruitment and retention of African Americans (or other highly religious) individuals into science. I have found that most of my highly religious Christian students have never really discussed the foundation of their theological views. As a confirmed Episcopalian, these are conversations I have learned how to conduct in ways that do not automatically shut down critical reasoning. Indeed, there is variation within Christian denominations with regards to their willingness to accept evolution as compatible with their faith. In general, doctrinally conservative Christians reject evolution (Berkman and Plutzer 2010). For example, the Southern Baptist Convention (formed as the Pro-segregation Baptist Church in the 1920s) and the National Baptist Convention (predominately African American membership) both reject evolution as compatible with their faith; on the other hand, the Catholic Church accepts evolution as compatible with their faith (Martin 2010). Notably there is variation within the individuals who subscribe to major denominations concerning their acceptance of evolution. For example, for Doctrinally Conservative Protestants, surveyed from 1994 to 2004, those who felt that: humans developed from earlier species of animals 76% felt that this statement was definitely false or probably false, while 24% felt it was probably true or true. Similar values were recorded for Black Protestants, 66% and 35% respectively, for mainline Protestant denominations, the values were 45% and 55%; while for Roman Catholics, the values were 42% and 58% (Berkman and Plutzer 2010). Thus while a given church’s official position is to accept or reject evolutionary science, individuals within denominations tend to make up their own minds concerning evolution. I have found that exposing my highly religious students to the fact that that there is variation within Christian thought concerning evolution helps them be able to engage it critically while not feeling that they are abandoning their faith.

Yes, that’s one way to do it, and it’s a lot easier if, like Graves, you’re religious. Another, which a colleague mentioned to me yesterday, is to say, “You don’t have to change your religious beliefs to take an evolution course. All you need to do is study the contents of the course and answer the questions.” (This works for required evolution courses.) Although this may seem callous, to me it involves less dissimulation, for, to be truthful, most Christians do believe something that’s incompatible with the theory of evolution, even if that belief is just that God helped the evolution of only one species along H. sapiens.

All of these authors (save Bergman) are well meaning, and I’m with their goal: everyone deserves a chance to study evolution.  But the solutions involving religion, eugenics, affirmative action, and the like seem like Band-Aids on the wound.

There is only one workable solution, and that’s ensuring equal opportunity for all Americans. I won’t go into the problems with that solution, which may be insuperable, but should we be discussing that solution before we get to eugenics and religion?

Misconceptions about evolution

June 14, 2023 • 9:35 am

Over the 14 years (can it be that long?) that I’ve been writing this website, I’ve put up several lists of misconceptions about or misrepresentations of evolution, but they’ve all been compiled by other people (for example, see here, here, and here). Some of them aren’t really misconceptions, such as the second link, which lists “misrepresentations” that are really pieces of advice about how to teach evolution.  Those are generally good, though I can’t say I agree fully with this one: ““Avoid giving the impression that evolution is atheistic, or that evolutionists must be atheists.”

The way I teach evolution, starting with two sessions on why we accept evolution (these lectures were turned into Why Evolution is True), involves a certain amount of creationism-bashing. That’s because I use the rejection of creationism in favor of evolution in the late 18th century as an example of the way science proceeds: theories are discarded when they become increasingly incompatible with the evidence, while the alternative theory (evolution in this case) is able to explain facts that stymie creationism. The fossil record, anomalies of development, vestigial organs, and (my favorite) biogeography are all areas in which evolution explains phenomena that can’t be explained by Biblical creationism.

Now it wasn’t I who made this argument, but Darwin. If you read On the Origin of Species, which Darwin himself characterized as “one long argument,” you’ll see that he’s constantly opposing creationism with evolution without going too hard after Christian creationism (Britain wasn’t full of fundamentalists like America is now). Describing the imbalance of organisms on oceanic islands, for instance, was a very clever way that Darwin showed how evolution could explain phenomena that baffled creationists. In fact, I’ve never seen a good creationist explanation of biogeography, especially of the “unbalanced” nature of life on oceanic islands: the lack of endemic mammals, amphibians, and freshwater fish while there are plenty of endemic insects, plants, and birds.

But teaching this way offended a few of my religious students, who called me out for “creation-bashing” in my evaluations. I reject that criticism, for, after all, creationism was THE going explanation for life and its patterns before Darwin, and within a decade his compelling arguments had vanquished that explanation. Teaching this way, I think, is a good object lesson in how science is done (yes, creationism was a scientific hypothesis before Darwin), as well as educating the students on why nearly all scientists accept the fact of evolution.  And I took this approach in Why Evolution is True. The usefulness of opposing two theories and adjudicating them with evidence is supported by the success of that book—far greater than I expected.

I don’t say anything about atheism in my classes, for that’s not part of my job, but most students do get the idea that the Bible should not be taken literally as a theory of biology. And if they ask me my views about gods straight out, I will be honest with them.  Further, if they ask me, according to the guidance in bold above, whether religion and evolution (or science in general) are compatible, I will explain to them (privately, because the explanation is long) that while one can be religious and accept evolution, they are incompatible in a fundamental way: one accepts religious “truths” based only on authority, dogma, or scripture, while science accepts empirical truths based on evidence and the consensus of scientists.  (Yes, religions do make truth claims.) That is why I wrote Faith Versus Fact.  But I’ve never had a student complain that I’ve said that either evolution or science are atheistic, for I have never claimed that in lecture. It is of course true in an important way, for a practicing scientist rejects the idea that what he/she is investigating could have divine explanations.  You leave your faith at the door of the lab. (I won’t reiterate my incompatibility claims here; read FvF if you want to see my argument.)

In that sense, then, science is atheistic, for it rejects belief in gods. Let me emphasize that, as I say in FvF, that this rejection is not by a priori agreement: scientists didn’t get together in some smoke-filled room and agree to reject gods, despite some creationists who claim that.   Indeed, there were times in science, like early astronomy or when Biblical creationism reigned, that divine explanations were part of science.  But since they haven’t proven useful in explaining anything, we now reject them as being useless.  The best expression of this idea is the conversation that supposedly took place between the Emperor Napoleon and the French polymath Pierre-Simon Laplace in 1802, after Napoleon had been given Laplace’s five-volume work on celestial mechanics.  There are many versions of this conversation,  which may never have taken place, but here’s one from British mathematicial Walter Ball, published in 1888:

“Laplace went in state to Napoleon to accept a copy of his work, and the following account of the interview is well authenticated, and so characteristic of all the parties concerned that I quote it in full. Someone had told Napoleon that the book contained no mention of the name of God; Napoleon, who was fond of putting embarrassing questions, received it with the remark, ‘M. Laplace, they tell me you have written this large book on the system of the universe, and have never even mentioned its Creator.’ Laplace, who, though the most supple of politicians, was as stiff as a martyr on every point of his philosophy, drew himself up and answered bluntly, ‘Je n’avais pas besoin de cette hypothèse-là.’ [‘I had no need of that hypothesis.’]

Even if the conversation never happened, the anecdote explains why science is atheistic in practice: we have no need of that hypothesis.

But I digress. In August I’m lecturing to people on a cruise to the Galápagos Islands, which of course were visited by Darwin on the Beagle.  I’m giving two lectures on that trip, “Darwin on the Galápagos” and “Why evolution is true”, as well as a Q&A session with two five-minute mini-lectures.  But first let me point out two widespread misconceptions about Darwin and the Galápagos islands, which I won’t go into here but will do on the voyage:

  1. Darwin did not have an “aha moment” in the Galápagos islands when suddenly evolution and natural selection became clear to him.
  2. The famous “Darwin’s finches”, while they did play some role in Darwin’s thinking that led to The Origin, did not play a major role. He doesn’t even mention the finches in that book, and barely mentions the Galápagos (only 16 times). Other data and ideas were more important to the revolution in thought wrought by Darwin.  If you want to read about his adventures on the islands, read Chapter XVII of  the earlier The Voyage of the Beagle, “Galapagos Archipelago.”  It’s free online at the link.

But I digress again. I have 5-10 minutes to explain to the guests what the biggest misconceptions about evolution are, so of course I have to leave some out. But the list is designed to inspire discussion, so here it is:

  1. Evolution is “only a theory”
  2. In evolution, everything happens by accident
  3. Natural selection transforms individuals over time (in reality, individuals don’t change, but populations and species)
  4. Evolution operates “for the good of the species”
  5. Evolution is inherently progressive
  6. Evolution equips organisms to face challenges that arise in the future
  7. Humans are no longer evolving

I could of course give more, but these are the seven I’ve chosen to explain, and I hope I can do it in no more than ten minutes. (I’m leaving out details and hope that they’ll come out in audience discussion.)

I may give summaries of my other minitalks here later (on the ship I’ll ask people which one(s) they want to hear), which include “What evidence would disprove evolution?”, “What IS the theory of evolution?”, and “Why do so many Americans reject evolution?”.

**********

Here’s a first-edition of On the Origin of Species in a presentation copy. (I’m not sure what that is for the handwriting is surely not Darwin’s.) Only 1250 copies were printed, and this one goes for $950,000:

The NYT oversells a new report of a “virgin birth” in crocodiles

June 8, 2023 • 9:30 am

This is an example of science reporting that’s misleading—not because it gets the facts wrong, but because it oversells a rather mundane finding as a potentially important insight into the life of the extinct dinosaurs.  And no, there’s nothing in the original paper—about a single “virgin birth” in a crocodile (really a “stillbirth”)—to suggest the Big Sell: that dinosaurs could have reproduced via “virgin births”, too. Dinosaur Jesus probably didn’t exist.

So here we have one new paper from the Royal Society’s Biology Letters; click on first screenshot below to read (the pdf is here) reporting the occurrence of parthenogenesis in one crocodile in one zoo. The NYT Trilobite reports about it in the second screenshot below (I found it archived here).

Parthenogenesis is a form of asexual reproduction that occurs without the fusion of a sperm and an egg. It occurs across various animal taxa, and can arise in different ways.  Here’s what Wikipedia says about its distribution (note that it doesn’t occur naturally in mammals).

Parthenogenesis occurs naturally in some plants, algae, invertebrate animal species (including nematodes, some tardigrades, water fleas, some scorpions, aphids, some mites, some bees, some Phasmatodea and parasitic wasps) and a few vertebrates (such as some fish, amphibians, reptiles and birds).

Parthenogenesis can occur in a variety of ways, often after hybridization between species that produces an individual whose chromosomes can’t pair properly during meiosis (cell division producing sexual gametes). That mispairing increases the likelihood that an unfertilized egg in a hybrid can have a full chromosome complement and develop into an offspring. But in most other cases, like this one, asexual reproduction occurs as a modification of non-hybrid meiosis.  That’s what apparently happened in this case.

The authors report that an 18-year-old American crocodile (Crocodylus acutus) in a reptile park in Costa Rica laid a clutch of 14 eggs. Candling of the eggs (holding them up to the light) revealed that seven apparently contained embryos (or dense spots), but none developed to hatching. One fetus, however, almost made it, and when the egg was dissected it contained a single female. Here’s the photo from the paper: mom on top and the fetus at the bottom. There was clearly something wrong with the baby as it failed to hatch, and I suspect it was simply screwed up.

(From paper): Figure 1. (a) Adult American crocodile, Crocodylus acutus. Photo courtesy of Q. Dwyer. (b) Stillborn fetus of American crocodile, Crocodylus acutus, Parthenogen. Photo courtesy of Q. Dwyer.

Genetic analysis of the fetal DNA compared to mom’s showed that they were pretty much genetically identical, with the fetus being, in effect, a clone of the mother.

How did this happen? If you don’t need the details, skip this next part between the lines.

DNA results from the paper suggest that the fetus came from fusion of two of the products of meiosis. Here’s a diagram of how a female produces an egg (or a male produces a sperm) during meiosis (figure from Wikipedia). It entails doubling of each of the chromosomes in a sperm or egg precursor cell followed by two bouts of cell division.  The circle on the extreme left is of the precursor gamete cell in a species having four chromosomes, with two copies of each of two different chromosomes (remember, we have two pair of every chromosome).  Then each pair doubles, which happens during normal cell division (mitosis) as well as in meiosis (second circle).

But then meiosis begins in gonadal cells: instead of each doubled chromosome splitting and going to a new cell, producing two genetically identical cells (this is normal cell division), the chromosome twins of each pair, now doubled (and having reshuffled bits from meiotic “recombination”), go into separate cells (third circle from left).  This is the first phase of meiosis, or “meiosis I”.  Now we have two daughter cells, each containing two chromosomes that are doubled but connected by the centromere. The chromosome number is really two, not four, because these doubled chromosomes (called “chromatids”) are going to go to different cells.

During “meiosis II”, the doubled chromosomes of each pair split, with each going to a new cell, so instead of two pair of joined chromosomes, we simply get two single chromosomes.  The chromosome halves can sort out independently of each other, which is called “segregation”, and is one way to recombine existing genes. In the end, a cell with four chromosomes has, though doubling and then two  cell divisions, produced a “haploid” cell with only two chromosomes. These final cells have only one instead of two copies of each chromosome pair. They are the gametes: eggs and sperm, and are shown on the extreme right.  This happens in eggs and sperm, and when they fuse, the normal chromosome number is restored. You can see that when this happens in both sexes, you get novel combinations of parental genes—one of the likely reasons why sex evolved.

Now, how did this produce the parthenogenic crocodile fetus?  In females, usually only one of the four products of meiosis goes on to form the haploid egg, with the other three cells being segregated into “polar bodies” that eventually die. But sometimes a polar body will fuse with the egg cell, restoring the normal chromosome complement and producing a diploid individual having two copies of each chromosome.  It’s a bit more complicated than this , but the result is that a female can produce a normal diploid offspring without being fertilized. This is simply because two of the halved cells that would normally become egg cells fuse with each other.

Using DNA sequencing, the authors confirmed that this is what happened (the formal process is called “automictic parthenogensis with terminal fusion”). But the diploid fetus, which would normally go on to form a crocodile that would hatch, was somehow inviable.

Note that this is the first report of parthenogenesis in a crocodile. (Since the mother was 18 and had been alone since she was two, it was extremely unlikely that the fetus came from her storing sperm after being inseminated sixteen years before, as some animals can store sperm for a substantial period.)

So far so good. And the NYT article below gets the details and facts right. Where it goes off the rails is instantiated in the sub-headline.  (The big headline is wrong, too: this is NOT a “virgin birth” but a virgin stillbirth. No new croc entered the world. 

Because crocodiles are related to the extinct dinosaurs, author Greenwood (and the authors of the original paper), suggest that this is a case of “facultative parthenogesis that could also have occurred in dinosaurs! Dinosaurs could have reproduced asexually! T. rex could have produced baby T. rex copies without having to mate! Note the subheadline above, mentioning “Jurassic Park”.)

The article also says this:

So, did dinosaurs do it, as the discovery of parthenogenesis in crocodiles suggests? Parthenogenesis is best confirmed with DNA analysis, a process that has allowed scientists to tell it apart from delayed conception, where a female stores sperm for as long as six years before using it to fertilize eggs. Without the ability to retrieve dinosaurs’ and pterosaurs’ DNA, which does not persist in fossils, certainty is not available.

“We’ll never be able to prove they could do it,” Dr. Booth said. “But it suggests they had the ability.”

My response is “no, it doesn’t.”

But at least both the authors and the journalist say we can’t prove that there were Jesus-saurs, but I’d go further and argue that this is speculation far beyond what’s warranted from the data—speculation prompted by the desire to jazz up what is a decent but not terribly exciting result. In fact, I’d say that because the single dead offspring represents a bug and not a feature of croc reproduction, it says absolutely nothing about the likelihood that dinosaurs reproduced asexually, much less that they did so “facultatively”—as a regular evolved feature of their lifestyle.

First of all, this isn’t really “facultative parthenogesis,” which refers to species that can produce normal offspring sometimes via sexual reproduction and sometimes asexually. (That might be an evolved property, allowing an individual to pass on its genes when populations are sparse and there is nobody around to mate with.)

This isn’t what’s going on with crocs.  What we see here is probably a rare developmental screwup (it hasn’t been reported before, despite there being many captive crocs), an anomaly that is an evolutionary dead end.  Rare parthenogensis has been seen in other species too, including birds (see below), but in those species results in largely inviable or infertile offspring.  True “facultative parthenogenesis” isn’t common, but does occur in some creatures like lizards. And it’s not a bug, but an evolved feature.

Below I show the family tree of some vertebrates, including the dinosaurs, birds, lizards (one of the “squamates” along with snakes), and the crocs. (This slide was created by my friend Phil Ward, who teaches evolution at UC Davis.) You see that the crocs are related to dinosaurs, but not as closely related as are living birds, which are a group (“clade”) phylogenetically embedded within the now-extinct dinosaurs.

The upshot is that a rare occurrence of asexual reproduction, especially when it leads to a dead or sterile offspring, says nothing about the likelihood of facultative parthenogenesis in a relative. After all, birds are more closely related to dinosaurs than are crocs, and a couple of birds have reproduced asexually (turkeys can produce fertile offspring this way, though rarely, and California condors have also done it). But nobody goes shouting from the rooftops “dinosaurs could have reproduced asexually” because of a few rare cases in birds.  Quite a few lizards reproduce normally by parthenogenesis, but you don’t hear people extrapolating from lizards to dinosaurs, either.  Even some fish reproduce parthenogenetically, so why not write that “because fish are related to dinosaurs, dinos could also have reproduced parthenogenically.”?  It’s all pilpul.

The facts in the NYT report are accurate, including the caveat that we can’t test the asexual-dino hypothesis, but the author couldn’t resist bringing in the dinosaur angle—without any good reason to do so.  What will happen is that people will ignore the fact that the single parthenogenic crocodile fetus was stillborn (or “stillhatched”), was probably just a rare developmental anomaly, and go away instead with the lesson that “DINOSAURS COULD HAVE REPRODUCED BY CLONING THEMSELVES!!!”.

How did warning coloration evolve?

June 5, 2023 • 9:30 am

Aposematic coloration, often called “warning coloration”, is the presence of bright or conspicuous colors or patterns in animals that are toxic, noxious, dangerous, or poisonous to predators. Here’s an example from Wikipedia, the granular poison frog (Oophaga granulifera). Like many dendrobatid frogs, this has a number of poison alkaloids in its skin, and they have been used in Central and South America to tip arrows or darts, which can kill mammals. Any predator that tried to eat one of these would probably be dead, or at least very ill.

My own frog, Atelopus coynei, looks conspicuous too [but see Lou Jost’s comment below], and may be toxic, but I don’t think people know anything about that:

Atelopus coynei. Photo: Jordy Salazar/EcoMinga

But of course far more animals than amphibians are aposematic. The skunk advertises its toxicity with a pair of conspicuous stripes. Many insects, like ladybugs and some leipidopterans, are also aposematic and toxic, including at least one bird species: see here for a Google image search of aposematic animals.

The colors and patterns, as the name implies, gives their bearers an evolutionary advantage over their presumably camouflaged ancestors, for predators will deliberately avoid the pattern, usually because they’ve learned to recognize and stay away from it because of previous unpleasant experiences. (The avoidance can also be evolved rather than learned, as you’ll see if you think about it. Even if eating one of these kills you, individual predators having less of a propensity to attack the pattern would be favored.)  Usually, however, learning is involved.

But to get that advantage, the aposematic species has to be sufficiently numerous to afford predators a chance to learn and then avoid the next aposematic animal. And this creates an evolutionary problem.

We are pretty sure that aposematic species evolved from camouflaged ones. To get the warning coloration started, there have to be mutations in the camouflaged population that produce individuals with bright colors and patterns, at least in incipient form.

And that’s the rub: the first mutant individual stands a higher chance of being attacked and killed than do cryptic individuals. Even if it’s toxic, it may still get killed or injured by being attacked for being a novel, conspicuous creature.  So how does the adaptation ever spread through the population from a rare initial state?

Previously, as described in the excellent Nature News & Views summary by Tim Caro below (click to read), we had a few answers:

1.) The trait could evolved by kin selection in gregarious animals. While the first mutant individual might be attacked, it might be part of a group of relatives that share that aposematic mutation. Assuming the predator learns to avoid the pattern after killing or hurting the first individual, it would avoid its similarly-colored kin, and that is a form of kin selection on the color/pattern genes that could make them spread.

2.) The trait could have evolved from a state that was conspicuous but not as conspicuous as the animals above. But this runs into the same problem as #1!

3.) The attacked aposematic mutant could avoid being killed by the predator because it smells or tastes bad, or is injured only slightly. If the predator learns from one experience (and some do), then that individual would henceforth be protected from predation, perhaps giving the mutant color/pattern gene an advantage. This seems somewhat likely, and could be tested by exposing naive predators to aposematic prey.

4.) Predators might avoid novel colors or patterns in general since the hunters have a search image for edible species. As Caro says, there’s some evidence for this, too.

But now, in his summary of the original paper, Caro describes a fifth hypothesis that is described in the Science paper below that.  The authors test this interesting hypothesis using phylogenetic data, and it seems to be supported.

Click the original Science paper below to read about the novel hypothesis for the evolution of aposematism. The authors test it in amphibians, but may hold for other creatures as well. You can also find the pdf here , and the reference is at the bottom. 

Again, I’ll try to be brief, but may not succeed. The authors’ hypothesis, which is very clever, is that full aposematic coloration may have evolved, at least in amphibians from an earlier state where it wasn’t clearly visible to predators. This could involve the colors/patterns starting their evolution on the BOTTOM (ventral) side of the animal, which wouldn’t draw attention until the animal was attacked, at which point it could flash its pattern and possibly startle the predator (the predator could also learn from a brief encounter that the prey was toxic).  And the bottom-colored state could itself be of two types: small patches on the ventral surface (PV) or a fully colored ventral surface (FV). This is in contrast to an animal that is fully colored all over its body.

Once the predator started learning what the color/pattern means from the animals that had it on their belly, then the color could evolve to cover the animal, making it fully aposematic.

But how do you test this hypothesis? Well, you could see if predators learn to avoid toxic amphibians that had color patches painted on their belly, but there are few amphibians that are toxic and lack aposematic coloration. No, the authors tested their hypothesis by doing phylogenetic reconstruction: they used living species and their known family tree to deduce what the color/pattern of the ancestors were. This kind of reconstruction, which makes sense if you have enough data, is increasingly used to study evolution.

And so Loeffler-Henry et al. did a big reconstruction of the evolutionary history of amphibians, many of whom were aposematically colored. They used 1106 species, putting each in one of five evolutionary categories:

species cryptic (camouflaged; “cry” in photo below)
species PV (ventral side partly aposematic)
species FV (ventral side fully aposematic)
species fully aposematic all over its body (“conspicuous” or “con” in photo below)
species polymorphic (some individuals are aposematic, others not). There aren’t many of these, and I won’t go into why they are supposed to exist.

Here’s a photo from the paper showing four of the five states (a polymorphic species isn’t shown):

Part of paper’s caption: Cry: cryptic; PV (partially conspicuous venter): cryptic dorsum with conspicuous color present as small patches on normally hidden body parts; FV (fully conspicuous venter): cryptic dorsum with conspicuous colors fully covered on the venter; Con: conspicuous

And here’s the reconstruction of the phylogeny showing the position in the family tree of each of the five states. Click to enlarge:

(From paper): Fig. 2. Ancestral state estimation of each color state (N = 1106 species) in frogs and salamanders. Pie charts at each node show the probabilities of ancestral states. The ancestral state of frogs and salamanders is likely to be cryptic coloration. The hidden color signals (PV and FV) are widespread and have evolved multiple times in different lineages. PV: cryptic dorsum with conspicuous color present as small patches on normally hidden body parts; FV: cryptic dorsum with conspicuous colors fully covered on the venter. See table S11 for photo credits.

There’s a pie diagram at each node of the tree showing the probability that that ancestor had one of the five states scored. I won’t go into the methods for deriving probabilities (in truth, I don’t understand them); but her are the salient points:

1.) Ancestors tend to be cryptic (camouflaged; gray dots), with the possible exception of some salamanders. This comports with the evolutionary view that aposematic coloration was not an ancestral condition but evolved as a defensive adaptation to deter predators.

2.) Full aposematism—the orange state—didn’t appear until later in amphibians, and

3.) . . . it did so generally going through an intermediate state of aposematic coloration on the belly (purple and red species)

4.) The preponderance of purple circles earlier than red ones suggests that the condition of full ventral coloration was preceded in time by the evolution of partial ventral coloration: patches of color that could be flashed but are still less conspicuous to predators than fully belly coloration. This suggestion is supported by statistical analysis of the likelihood of the models, but I’ll skip that.

Now this is an analysis of amphibians, but could apply equally well to other species. In fact, many butterflies that have warning coloration have it on their rear wings, which are covered up when they’re resting. It’s only when they fly, or when a predator startles them, that the aposematic coloration is revealed. Here’s an example: an aposematic butterfly from Ray Cannon’s Nature Notes. It’s the common birdwing (Troides helena), known to be very poisonous since the larvae feed on plants containing toxic aristolochic acids.

And here’s a fully aposematic butterfly:

(from site): Altinote dicaeus callianira – its distinct pattern advertises its unpalatability. Photo: Adrian Hoskins

For a long time the evolution of aposematic coloration posed the problem of what evolutionists call an “adaptive valley”: how do you get from one adaptive state (toxic but camouflaged) to a presumably more adapted state (toxic and brightly colored), when the intermediate evolutionary stage (the first mutant individual) was at a disadvantage: mired in an adaptive valley?  This could not occur by natural selecction since selection cannot favor the less adapted (here, “less avoided”) individuals.

The authors propose a solution to this: an adaptive valley wasn’t crossed because the intermediate state—ventral coloration—did confer a selective advantage on the first mutant individuals.

The authors end the paper by suggesting that their scenario could apply to many species; and it well could:

. . . macroevolutionary studies on animal coloration should take into account these underappreciated hidden signals, which are both common and widespread across the animal kingdom, to advance our understanding of the evolution of antipredator defenses. Indeed, many animal taxa such as snakes, fishes, and a variety of arthropods (see fig. S12 for example groups) include species that are cryptic, are aposematic, and have hidden conspicuous signals. We therefore encourage follow-up studies in other taxa to evaluate the generality of the stepping-stone hypothesis as a route to aposematism.

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Loeffler, K., C. Kang, and T. N. Sherratt.  2023. Evolutionary transitions from camouflage to aposematism: Hidden signals play a pivotal role. Science 379:1136-1140. DOI: 10.1126/science.ade5156