This makes total sense. Dan takes a pretty left-brained, mechanistic approach to the relationship problems brought before him. Click and Clack talk about relationships almost as much as they discuss cars. Many times, I’ve run across relationship and automotive problems of my own that seemed like they would be worthy of a phone call to the appropriate show—only to realize I already knew the answer thanks to long hours of listening to advice given to other people.
Also, I’ve heard that almost a third of Dan’s misanthropic snark is added in post-production.
Via Dan Savage. I’m still waiting to hear what the Car Talk guys think.
Via HiLoBrow: 3eanuts removes the fourth panel from “Peanuts” cartoons, and with those fourth panels goes the leavening of humor from Charles M. Schulz’s bleak world. As the AV Club points out, this doesn’t necessarily make “Peanuts” any more depressing than it already was.
On a summer night in a Florida corn field, a female armyworm moth emerges from her underground cocoon and spreads her wings to dry in the humid air. Over the next few weeks, she will fly miles away in search of a mate, and a likely-looking patch of host plants on which to lay her eggs.
Her brief adult life will be shaped in many ways by the life she led as a larva, feeding on domestic corn. She could easily find other grasses to feed her offspring, but she’ll probably seek out another cornfield. She may encounter armyworm males who were raised on many other grasses, but the odds are that the males she accepts as mates will also have grown up eating corn. This is so likely to be the case that it has left a mark on the genetics of her species [PDF].
At night in a cornfield, moths mate nonrandomly. Photo by K e v i n.
Yet it isn’t clear how much of this isolation between armyworms from corn (the “corn strain”) and armyworms from other grasses (called the “rice strain”) arises because moths from the different host plants actively prefer mates from their own larval food plant, or because they just don’t encounter moths from the other food plants as frequently. Like many moths, armyworms of both sexes deploy pheromones to attract and woo mates—so maybe armyworms from the same food plant smell better to each other. On the other hand, corn-strain armyworms do more of their mate searching early in the evening (although they’ll keep hunting all night), while rice-strain armyworms wait to search till the last few hours of nighttime.
Disentangling which of these two sources of isolation—preference versus timing—maintains the genetic differences between host plant strains of the armyworm takes some careful experimental work. As in many biological questions, the answer might well be not one or the other, but a little of both [$a].
In a study published in the latest issue of The American Naturalist, a team of entomologists at the Max Planck Institute for Chemical Ecology took on the question of what keeps the armyworm host strains separated. They performed two mating experiments with laboratory-reared moths of both sexes from both strains.
First was a “no-choice” experiment in which moths were kept in a chamber with a single member of the opposite sex from their own strain, or the other strain. The test was repeated over three nights in a row. On the first night, females from the corn strain were less likely to mate with males of the rice strain than males of their own, and when they did accept rice-strain males, it wasn’t till later in the night. The second and third nights, though, corn-strain females mated about equally with males of both strains. Rice-strain females mated with males of both strains at about equal frequency all three nights, although they did so late in the night.
In the second round of experiments, moths were introduced into flight cages with one member of the opposite sex from each of the two host strains, so they could choose between them. To control for the differences in timing of mate searching between the two strains, the team repeated the experiment twice—in one version, the choosing moth had the entire length of the night to pick a mate, and in the other, the moths were only put into the same cage for the last four hours of the night, when the grass strain prefers to mate.
In the all-night experiment, corn-strain males and females were both more likely to choose a mate from their own strain than the other. Rice-strain moths of both sexes mated with moths of both strains about equally—but rice-strain females were less likely to choose any mate at all. On the other hand, when the research team waited till the end of the night to introduce the test moths to their possible mates, rice-strain moths of both sexes mated much more frequently overall, and rice-strain females strongly preferred rice-strain males. Corn-strain males were basically indiscriminate in the late-night experiment, and corn-strain females were also less choosy.
In short, when mating during their usual activity periods, females of both strains were choosy about their mates; but when offered mates at the wrong time, they didn’t discriminate as much. The authors suggest that these mistimed matings were less discriminating because they were more likely to be initiated by the males, who showed relatively weak preferences even during their own usual mating times.
So the genetic differentiation between armyworm host strains is probably due to both timing and mate choice, and the two isolating factors affect males and females differently. Females, particularly rice-strain females, are quite picky about mating with a male of their own strain. Males, on the other hand, seem mainly to be prevented from pursuing females of the other strain by the fact that their respective schedules don’t line up. As the study’s authors conclude, all these individual rejections and missed connections, added up across entire armyworm populations, bring these moths a little bit closer to speciation.
Prowell, D., McMichael, M., & Silvain, J. (2004). Multilocus genetic analysis of host use, introgression, and speciation in host strains of fall armyworm (Lepidoptera: Noctuidae). Annals Entomol. Soc. America, 97 (5), 1034-44 DOI: 10.1603/0013-8746(2004)097[1034:MGAOHU]2.0.CO;2
Schöfl, G., Dill, A., Heckel, D., & Groot, A. (2011). Allochronic separation versus mate choice: Nonrandom patterns of mating between fall armyworm host strains. The American Naturalist, 177 (4), 470-85 DOI: 10.1086/658904
Robert Kurzban responds in the ongoing“adaptive” homophobia kerfuffle (henceforth, the O.A.H.K.) with continued confusion about how biologists identify possible adaptations and test to see whether natural selection is responsible for them. He notes that one effect of natural selection is to remove heritable variation in traits under selection, so that many traits which are probably adaptations—arguably, sometimes the best-adapted traits—actually have zero heritability.
This is true. But it’s important to note that a trait having zero heritability, or no genetic variation, is not the same thing as that trait not being heritable, or having no genetic basis. If the trait has zero heritability, the observed variation in the trait may not be heritable, but the trait still may be. Kurzban’s confusion over this distinction may be a fault of the terminology, as was pointed out to me in a couple independent conversations following the last round of the O.A.H.K.
That aside, reduced heritable variation in a trait—relative to appropriate standards for comparison, like other traits in the same species or the same trait in closely related species—is sometimes used to infer that selection has acted on that trait in the past. This is what my lab has done in the case of Joshua tree and its pollinators, which Kurzban cites. This sort of approach provides only indirect evidence of natural selection’s activity—but it’s often the best you can do when your focal species isn’t amenable to growing in a lab or greenhouse within the span of a single grant cycle.
The two varieties of Joshua tree, because apparently these are part of the discussion now. Photo by jby.
The comparison to other traits or to other species is the critical point here. Without it, you can’t determine whether a lack of genetic variation is due to strong selection, or due to the fact that there is no genetic basis for the trait. In isolation, the observation that there is no heritable variation for a single trait or behavior in a single species doesn’t tell you much except that natural selection cannot currently be acting on the observed range of variation in that trait. If there’s no genetic basis for the trait at all, then it cannot have been under selection in the past, either.
Forming hypotheses versus testing them
Regarding Kurzban’s broader point about how biologists identify adaptations:
Futuyama’s textbook, which Yoder cites for the discussion of heritability, indicates the following: “Several methods are used to infer that a feature is an adaption for some particular function” (p. 261), and lists the criteria that evolutionary psychologists rely on, including complexity, evidence of design, experiments, and so on. From the material I quoted in my prior post, it seems to me that by indicating the two kinds of evidence that are necessary for inferring a feature is an adaptation, Yoder is rejecting Futuyama’s claim that one can infer adaptation from its form, complexity, and so on.
Here Kurzban is confusing how we initially infer that a trait or behavior might be an adaptation with how we actually demonstrate that a trait or behavior is an adaptation. Forming a hypothesis is not the same thing as testing it, as Jon Wilkins explained so well. If Kurzban is accurately representing evolutionary psychology’s standards of evidence, then he’s confirmed Wilkins’s accusation that evo psych usually doesn’t go beyond the step of forming a plausible hypothesis to collecting the data that can test it.
Demonstrating that an adaptive hypothesis is well supported by data is, as I’ve previously said, a lot of work—usually enough for more than one scientific article. Depending on what is easiest to do, building the case that a trait is an adaptation might start with a paper that merely demonstrates a trait’s function—but that trait has not been conclusively shown to be an adaptation until we know that its demonstrated function is selectively important, and that the trait itself has a genetic basis.
While familiar to anyone who reads the evolutionary biology literature, this maybe isn’t so obvious to non-biologists. This may be because popular science accounts don’t always differentiate between hypotheses with good scientific support and those with none. Walk through a zoo or a natural history museum, and you’ll read nothing but adaptive hypotheses all day—but you’ll rarely see good, deep discussion of how well they’re supported.
This is why, since I started graduate school, I’ve became rather tiresome company on trips to museums and zoos. But one of the great things about popular writing by working scientists (from my perspective as a scientist) is that it lets specialists explain exactly such finicky details of our fields directly to the public. Doing so clearly and accessibly is challenging, to be sure, but naïve, uncritical endorsements of unsupported hypotheses—about the adaptive values of human behavior, or anything else—are available in just about every major media outlet. If scientists don’t do better than that in our own science communication, what value do we have to add to the discussion?
And now something new: relevant data
Your reaction to this image might be in your genes, but the evidence is that it can change, too. Photo source unknown, presumed public domain.
Which brings us back to evaluating Gordon Gallup’s “adaptive” homophobia hypothesis. Kurzban also points to evidence (ye gads! data!) that natural selection actually could have something to work with in the case of attitudes towards homosexuals. A 2008 Australian twin study, which finds a genetic component of variation in responses to a questionnaire about attitudes towards homosexuality.
This is indeed, as Kurzban suggests, preliminary data in support of the idea that natural selection could operate on homophobia. As Neuroskeptic pointed out in the comments on my last O.A.H.K. post, it also means that natural selection could be operating on tolerance of homosexuals. It’s an interesting and important question, actually, why the authors of that study chose to frame their results as showing the heritability of intolerance, rather than the heritability of tolerance.
However, as I noted all the way back at the beginning of the O.A.H.K., we also know that homophobic attitudes can change considerably over the course of an individual’s lifetime. It’s hard to say how survey responses taken at a single point in time relate to what natural selection would actually have to work with, if homophobic attitudes or lack thereof somehow shape an individual human being’s expected reproductive fitness. Even if there is some solid genetic basis to homophobia, we still don’t have data that can rigorously determine whether or how natural selection might act on that variation.
Godsoe, W., Yoder, J.B., Smith, C.I., Drummond, C., & Pellmyr, O. (2010). Absence of population-level phenotype matching in an obligate pollination mutualism Journal of Evolutionary Biology, 23 (12), 2739-2746 DOI: 10.1111/j.1420-9101.2010.02120.x
Verweij, K., Shekar, S., Zietsch, B., Eaves, L., Bailey, J., Boomsma, D., & Martin, N. (2008). Genetic and environmental influences on individual differences in attitudes toward homosexuality: An Australian twin study. Behavior Genetics, 38 (3), 257-265 DOI: 10.1007/s10519-008-9200-9
Jesse Bering has responded to criticism—by me, Jon Wilkins, and P.Z. Myers, among others—of his post about Gordon Gallup’s hypothesis that fear of homosexuals is favored by natural selection, in the form of an interview with Gallup. The result is informative, but probably not in the way intended.
To recap: Gallup proposed that homophobia could be adaptive if it prevented gay and lesbian adults from contacting a homophobic parent’s children and—either through actual sexual abuse or some nebulous “influence,” making those children homosexual. In support of this, he published some survey results [$a] showing that straight people were uncomfortable with adult homosexuals having contact with children.
I pointed out that all Gallup did was document the existence of a common stereotype about homosexuals—he presents no evidence that believing this stereotype can actually increase fitness via the mechanism he proposes, or that it is heritable.
Homophobia. And, um, everyone-else-phobia, too. Photo by yksin.
So now Gallup and Bering have responded, although they have not, I think, improved their case. There’s a lot for me to address here, so I’ll try to break it up into sections, and follow the order of the interview.
In which Gordon Gallup is not a homophobe
In the response post, Gallup (and Bering, who contributes quite a lot to the argument in his role as interviewer) takes issue with the collective objections of working biologists, but manages not to actually address those objections. Bering starts the conversation on the moral high ground:
BERING: Let’s address the elephant in the room. It’s embarrassing for me to even ask this of you, since the answer is so obviously “no” to me. Is your theory a justification of your own homophobia?
GALLUP: A lot of people think that if a person has a theory it’s a window unto their soul. I have lots of theories. (See CV (pdf).) I have a theory of homophobia, I have a theory of homosexuality, and I have a theory of permanent breast enlargement in women, just to mention a few. So that would make me a homophobic, homosexual who is preoccupied with women’s breasts.
Neither I, nor any of the other critics I’ve seen have called Gallup a homophobe. He may be uniquely bad at understanding how societal homophobia nullifies his interpretation of his survey results, but that doesn’t make him a homophobe. Thanks for clearing that up, though, guys.
Gallup then demonstrates that he either hasn’t actually read any of the latest criticism, or has missed the point entirely:
… It is interesting how my critics tip-toe around the fact that my approach is based on a testable hypothesis, and how they go out of their way to side-step the fact that the data we’ve collected are consistent with the predictions. Whether it is politically incorrect or contrary to prevailing social dogma, is irrelevant. In science, knowing is preferable to not knowing. Minds are like parachutes, they only function when they’re open. If I were a homosexual, I’d want to know about these data.
I certainly didn’t tiptoe around the testability of Gallup’s hypothesis—I wrote that (1) the data he presented do not test his hypothesis, and (2) the data we do have regarding the probable fitness benefits of homophobia and its heritability contradict his hypothesis. I’m entirely prepared to revise my conclusions given new data, but Gallup doesn’t have any.
In which at least one of us doesn’t understand heritability
In his next question to Gallup, Bering accuses me of “bungling” the definition of heritability, linking to evolutionary psychologist Rob Kurzban, who says that my brief definition of heritable as “passed down from parent to child more-or-less intact” is wrong because heritability is actually “the extent to which differences among individuals are due to differences in genes.”
Wow, dude. You are aware that what you just said means exactly the same thing as what I originally said, right?
Let’s go to the textbooks that Kurzban says I’m contradicting. Here’s the passage on heritability from Douglas Futuyma’s gold-standard undergraduate textbook Evolution (page 209):
One way of detecting a genetic component of variation, and of estimating VG [trait variation attributable to genetic differences] and h2 [the proportion of total trait variation explained by genetic variation], is to measure correlations* between parents and offspring, or between other relatives. For example, suppose that in a population, the mean value of a character in the members of each brood of offspring was exactly equal to the value of that character averaged between their two parents (the MIDPARENT MEAN) (Figure 9.20A). So perfect a correlation clearly would imply a strong genetic basis for the trait. [Bold text and bracketed notes mine; otherwise sic.]
The asterisk in that quote leads to a footnote pointing out that regression, rather than correlation, is more typically used. This is the definition of heritability that I learned in my undergraduate and graduate courses. It’s also the definition I’ve just helped teach to a class of third- and fourth-year undergraduate biology students in my capacity as a teaching assistant on a course in population biology.
In non-statistical terms (the kind I try to use on this blog), a positive regression between a parent’s traits and those of their offspring means, in fact, that the parent’s traits are passed on to their offspring, um, more-or-less intact.
Parent-offspring regression is widely used to estimate heritability [PDF], but you can also do similar analyses using trait measurements for siblings, or multiple generations on a pedigree. In all of these cases, known parental or sibling or familial relationships are proxies for genetic similarity—you can estimate heritability without knowing anything about specific genes. (In fact, sometimes biologists use genetic data to reconstruct pedigree relationships, then estimate heritability from the pedigree.) As implied in the quote from Futuyma’s textbook, this approach is statistically equivalent to showing that there is a significant portion of trait (phenotype) variation explained by genetic variation—which is where Kurzban seems to have become confused.
Wild parsnip, mostly here to break up the wall of text. Photo by Bas Kers.
Here’s a specific example near and dear to my field of study, species interactions: To determine whether parsnip webworms could be under natural selection to resist nasty chemicals produced by their food plant, the wild parsnip, May Berenbaum and Arthur Zangerl estimated the genetic component of variation [$a] in the worms’ capacity to choose food with lower levels of the toxins, and to tolerate the toxins they did eat. To do this, they raised webworm larvae of known parentage in the lab, and tested them on controlled diets. Their actual statistical analysis tested for an effect of the worms’ sibling relationships (parentage) on their ability to avoid toxins and survive them.
In all of Gallup’s lengthy response to Bering’s question about heritability, he doesn’t say a word about this kind of data with regard to homophobia. That’s because it doesn’t exist, and, as far as I can tell from the interview, he has no intention to try and collect it. To be completely fair, it’s harder to collect heritability data on humans than on webworms—but it’s hardly impossible. As Gallup notes, there are studies documenting heritability for, of all things, human grip strength [PDF].
Kurzban’s critique is correct in one very specific regard, which Bering doesn’t touch on. It is relatively difficult, both for logistic and resource-related reasons, to estimate a trait’s heritability and determine whether natural selection is acting on it within the same study. (Although there are plenty of exceptions—here’s one example [$a] pulled at random from my reference library.) That’s why I said, in my original post, that biologists expect evidence for heritability or fitness benefits in support of an initial claim that a trait or behavior is adaptive. The study I cited as an example of support for adaptation—which shows that horned lizards’ horns prevent predator attacks [PDF]—demonstrates fitness benefits, but not heritability. This point should be familiar to anyone who regularly reads the evolutionary biology literature.
So, again, Gallup has no data on the heritability of homophobia. The rest of his interview shows that he still doesn’t have any data to demonstrate fitness benefits for it, either.
In which evidence of fitness benefits also remains absent
Gallup then comes to the question of whether a child who would otherwise be straight can be “converted” to homosexuality by early same-sex sexual contact.
As detailed in my 1996 reply to Archer, we’ve collected data from male homosexuals that show that most gay males don’t report getting a clear sense of their homosexual orientation until they have their first same-sex postpubertal sexual experience.
Most gay men don’t know for sure that they’re gay until they’ve actually, you know, tried gay sex? Quelle surprise. This is absolutely classic mistaking of correlation for causation, and it suggests that Gallup doesn’t know much about the actual experience of sexual minorities. When you grow up surrounded by straight people, it often takes very direct evidence to convince you that you’re attracted to people of the same sex. If same-sex activity shortly after puberty can cause homosexuality, wouldn’t parents be most concerned about homosexuals having contact with teenagers? At the risk of sounding like a broken record, this is yet another thing we can’t tell from Gallup’s survey data—he asked about pre-pubescent children, and in one case 21-year-old children, but not children who have just passed puberty.
Finally, Gallup deals with the relative risk that homosexuals will molest children. He does this by moving the goalposts for pedophilia:
There is also evidence that shows that the propensity to have sex with minors is positively correlated with promiscuity among homosexual males. Unlike heterosexual pedophiles, homosexuals who have sex with minors target young postpubertal victims.
That’s not pedophilia Gallup is talking about—that’s violation of age-of-consent laws. The comparison between heterosexual-identified pedophiles, who target children, and homosexuals who have sex with post-pubertal teens under the age of consent is, frankly, intellectually dishonest. By definition those are two different groups. The comparison to make is that between all homosexuals who have had sex with minors and all heterosexuals who have had sex with minors. I would imagine that, as Gallup basically admits in his next sentence, those two groups look much more similar.
So that’s where we stand: still no evidence that homophobia is heritable, and still no evidence that it provides a fitness benefit by preventing the homophobe’s children from becoming homosexuals. Gallup’s only data are still, over fifteen years after his initial publication, a set of survey responses that are consistent with any number of hypotheses for the origins of homophobia. Claiming that those data demonstrate an adaptive function for hatred of homosexuals doesn’t just fail the standards of evidence for evolutionary biology, it’s bad scientific reasoning.
In which we come to a conclusion of sorts
In a coda to the interview, Bering accuses me and his other critics of failing to engage with Gallup’s results. I think my previous discussion, and Bering’s response to it, speak for themselves. Bering has demonstrated to me that he doesn’t understand undergraduate-level biology, and that, as Will Wilkinson suggested, he’s more interested in ginning up controversy than scientific rigor. (On which point he wins, I suppose. D&T’s visit count went through the roof when P.Z. Myers linked here.)
Bering also makes some conspicuously uninformed speculations about my own experience and motivations. I won’t dignify that with a response except to say yes, Jesse, I’m gay, and you don’t know the first thing about what I have or haven’t encountered in the way of “palpable disapproval.” First and foremost, though, I’m a scientist. Contrary to what you seem to think, I love a good counterintuitive, paradigm-shifting hypothesis, but I also expect it to be supported with data.
Bering, however, is convinced that he’s established himself as a hard-nosed scientific iconoclast in opposition to all us stodgy, dogmatic, evidence-demanding biologists. He concludes,
So, I’ll continue to dredge up any old theory, no matter how meager the supporting data …
Clearly, Jesse, I can expect nothing more of you.
Arden, N., & Spector, T. (1997). Genetic influences on muscle strength, lean body mass, and bone mineral density: A twin study. Journal of Bone and Mineral Research, 12 (12), 2076-2081 DOI: 10.1359/jbmr.19126.96.36.1996
Berenbaum, M., & Zangerl, A. (1992). Genetics of physiological and behavioral resistance to host furanocoumarins in the parsnip webworm. Evolution, 46 (5), 1373-84 DOI: 10.2307/2409943
The common cuckoo is such a lazy parent that brood parasitism—laying its eggs in the nests of other birds—is built into its biology.
No bird will willingly adopt cuckoo chicks, which usually out-compete, and sometimes kill, their adoptive siblings. Given any hint that one of the eggs in her nest isn’t hers, a bird will eject the intruder. So cuckoos have evolved eggs that mimic the coloring of their hosts’ eggs—dividing the species into “host races” that specialize on a single host species, and lay eggs that mimic that host’s.
Cuckoo eggs (indicated by arrows) in the nests of three different host species. Illustration via The Knowledge Project.
Birds see the world differently than humans—where we have three kinds of color-sensitive cells in our eyes, they have four. This allows them to see colors in the ultraviolet range, which is invisible to us. Birds’ eyes also have an additional class of sensory cell that may help them perceive and discriminate among textures. So to study the match between cuckoo and host eggs, Stoddard and Stevens first had to figure out what each egg looked like to a bird.
A reed warbler feeds the cuckoo chick that has taken over its nest. Photo via Wikimedia Commons.
To do this, they developed a mathematical model of each host species’ vision. The model estimated how similar two eggs should look to a bird, given raw data about what colors of light the eggs reflect and the specific colors the bird can detect. Using the model, Stoddard and Stevens could then calculate the “overlap” between the colors and patterning of a host egg and the egg of a cuckoo specializing on that host species.
Stoddard and Stevens then applied the vision model’s measure of similarity to museum specimens of eggs from the cuckoo-parasitized nests of eleven European bird species. They found that cuckoo eggs matched their hosts’ quite well overall, but the match was best for cuckoos specialized on especially vigilant hosts. For each host, the authors looked up studies of egg rejection behaviors to calculate the probability that each species would eject eggs that didn’t look like their own. Species with higher ejection probabilities were parasitized by cuckoo host races whose eggs were better mimics.
The weather was lousy, but the coffee was excellent. Photo by andrewyang.
I spent most of my final spring break as a graduate student in Portland, Oregon, where I am not sure I saw direct sunlight even once. Who wants to get a tan over spring break, anyway? Regular posting resumes when I’m back in Moscow next week. If you “like” D&T on Facebook, you’ll get an alert about that right in your News Feed (TM). That’s a good thing, right?
Not sure this’ll be practical in Portland. Solar power systems became both cheaper and more efficient in the last twenty years, and they’re likely to keep doing so.
On Twitter, hectocotyli just pointed me to another discussion of the problems with Gordon Gallup’s case for an adaptive function to homophobia (and linked to my take in connection, for which, thanks). Jon Wilkins goes into more detail on the general problem that evolutionary psychology too often accepts plausibility as the standard of proof for adaptive hypotheses.
In fact, it is trivially easy to come up with a plausible-sounding evolutionary argument to describe the origin of almost any trait. More importantly, it is often just as easy to come up with an equally plausible-sounding argument to describe the origin of a hypothetical scenario involving the exact opposite trait.
I think Wilkins is a little too polite in some regards; Gallup’s hypothesis doesn’t even qualify as “plausible” in the context of what we know today about its ugly component assumptions. (And what, by the way, Jesse Bering should have known before dredging up Gallup’s articles from well-deserved obscurity.) Nevertheless, Wilkins broadens the discussion to address scientific reasoning more generally, and the post is worth reading in its entirety.