Tag Archives: evolution

elsewhere on the net

I’ve been swamped with work lately, so blogging has taken a backseat. I keep a text file on my desktop of interesting things I’d like to blog about; normally, about three-quarters of the links I paste into it go unblogged, but in the last couple of weeks it’s more like 98%. So here are some things I’ve found interesting recently, in no particular order:

It’s World Water Day 2010! Or at least it was a week ago, which is when I should have linked to these really moving photos.

Carl Zimmer has a typically brilliant (and beautifully illustrated) article in the New York Times about “Unseen Beasts, Then and Now“:

Somewhere in England, about 600 years ago, an artist sat down and tried to paint an elephant. There was just one problem: he had never seen one.

John Horgan writes a surprisingly bad guest blog post for Scientific American in which he basically accuses neuroscientists (not a neuroscientist or some neuroscientists, but all of us, collectively) of selling out by working with the US military. I’m guessing that the number of working neuroscientists who’ve ever received any sort of military funding is somewhere south of 10%, and is probably much smaller than the corresponding proportion in any number of other scientific disciplines, but why let data get in the way of a good anecdote or two. [via Peter Reiner]

Mark Liberman follows up his first critique of Louann Brizendine’s new “book” The Male Brain with second one, now that he’s actually got his hands on a copy. Verdict: the book is still terrible. Mark was also kind enough to answer my question about what the mysterious “sexual pursuit area” is. Apparently it’s the medial preoptic area. And the claim that this area governs sexual behavior in humans and is 2.5 times larger in males is, once again, based entirely on work in the rat.

Commuting sucks. Jonah Lehrer discusses evidence from happiness studies (by way of David Brooks) suggesting that most people would be much happier living in a smaller house close to work than a larger house that requires a lengthy commute:

According to the calculations of Frey and Stutzer, a person with a one-hour commute has to earn 40 percent more money to be as satisfied with life as someone who walks to the office.

I’ve taken these findings to heart, and whenever my wife and I move now, we prioritize location over space. We’re currently paying through the nose to live in a 750 square foot apartment near downtown Boulder. It’s about half the size of our old place in St. Louis, but it’s close to everything, including our work, and we love living here.

The modern human brain is much bigger than it used to be, but we didn’t get that way overnight. John Hawks disputes Colin Blakemore’s claim that “the human brain got bigger by accident and not through evolution“.

Sanjay Srivastava leans (or maybe used to lean) toward the permissive side; Andrew Gelman is skeptical. Attitudes toward causal modeling of correlational (and even some experimental) data differ widely. There’s been a flurry of recent work suggesting that causal modeling techniques like mediation analysis and SEM suffer from a number of serious and underappreciated problems, and after reading this paper by Bullock, Green and Ha, I guess I incline to agree.

A landmark ruling by a New York judge yesterday has the potential to invalidate existing patents on genes, which currently cover about 20% of the human genome in some form. Daniel MacArthur has an excellent summary.

what’s adaptive about depression?

Jonah Lehrer has an interesting article in the NYT magazine about a recent Psych Review article by Paul Andrews and J. Anderson Thomson. The basic claim Andrews and Thomson make in their paper is that depression is “an adaptation that evolved as a response to complex problems and whose function is to minimize disruption of rumination and sustain analysis of complex problems”. Lehrer’s article is, as always, engaging, and he goes out of his way to obtain some critical perspectives from other researchers not affiliated with Andrews & Thomson’s work. It’s definitely worth a read.

In reading Lehrer’s article and the original paper, two things struck me. One is that I think Lehrer slightly exaggerates the novelty of Andrews and Thomson’s contribution. The novel suggestion of their paper isn’t that depression can be adaptive under the right circumstances (I think most people already believe that, and as Lehrer notes, the idea traces back a long way); it’s that the specific adaptive purpose of depression is to facilitate solving of complex problems. I think Andrews and Thomson’s paper received a somewhat critical reception (which Lehrer discusses) not so much because people found the suggestion that depression might be adaptive objectionable, but because there are arguably more plausible things depression could have been selected for. Lehrer mentions a few:

Other scientists, including Randolph Nesse at the University of Michigan, say that complex psychiatric disorders like depression rarely have simple evolutionary explanations. In fact, the analytic-rumination hypothesis is merely the latest attempt to explain the prevalence of depression. There is, for example, the “plea for help” theory, which suggests that depression is a way of eliciting assistance from loved ones. There’s also the “signal of defeat” hypothesis, which argues that feelings of despair after a loss in social status help prevent unnecessary attacks; we’re too busy sulking to fight back. And then there’s “depressive realism”: several studies have found that people with depression have a more accurate view of reality and are better at predicting future outcomes. While each of these speculations has scientific support, none are sufficient to explain an illness that afflicts so many people. The moral, Nesse says, is that sadness, like happiness, has many functions.

Personally, I find these other suggestions more plausible than the Andrews and Thomson story (if still not terribly compelling). There are a variety of reasons for this (see Jerry Coyne’s twin posts for some of them, along with the many excellent comments), but one pretty big one is that is that they’re all at least somewhat more consistent with a continuity hypothesis under which many of the selection pressures that influenced the structure of the human mind have been at work in our lineage for millions of years. That’s to say, if you believe in a “signal of defeat” account, you don’t have to come up with complex explanations for why human depression is adaptive (the problem being that other mammals don’t seem to show an affinity for ruminating over complex analytical problems); you can just attribute depression to much more general selection pressures found in other animals as well.

One hypothesis I particularly like in this respect, related to the signal-of-defeat account, is that depression is essentially just a human manifestation of a general tendency toward low self-confidence and aggression. The value of low self-confidence is pretty obvious: you don’t challenge the alpha male, so you don’t get into fights; you only chase prey you think you can safely catch; and so on. Now suppose humans inherited this basic architecture from our ancestral apes. In human societies there’s still a clear potential benefit to being subservient and non-confrontational; it’s a low-risk, low-reward strategy. If you don’t bother anyone, you’re probably not going to get the girl impress the opposite sex very much, but at least you won’t get clubbed over the head by a competitor very often. So there’s a sensible argument to be made for frequency dependent selection for depression-related traits (the reason it’s likely to be frequency dependent is that if you ever had a population made up entirely of self-doubting, non-aggressive individuals, being more aggressive would probably become highly advantageous, so at some point, you’d achieve a stable equilibrium).

So where does rumination–the main focus of the Andrews and Thomson paper–come into the picture? Well, I don’t know for sure, but here’s a pretty plausible just-so story: once you evolve the capacity to reason intelligently about yourself, you now have a higher cognitive system that’s naturally going to want to understand why it feels the way it does so often. If you’re someone who feels pretty upset about things much of the time, you’re going to think about those things a lot. So… you ruminate. And that’s really all you need! Saying that depression is adaptive doesn’t require you to think of every aspect of depression (e.g., rumination) as a complex and human-specific adaptation; it seems more parsimonious to see depressive rumination as a non-adaptive by-product of a more general and (potentially) adaptive disposition to experience negative affect.  On this type of account, ruminating isn’t actually helping a depressed person solve any problems at all. In fact, you could even argue that rumination shouldn’t make you feel better, or it would defeat the very purpose of having a depressive nature in the first place. In other words, it’s entirely consistent with the basic argument that depression is adaptive under some circumstances that the very purpose of rumination might be to keep depressed people in a depressed state. I don’t have any direct evidence for this, of course; it’s a just-so story. But it’s one that is, in my opinion (a) more plausible and (b) more consistent with indirect evidence (e.g., that rumination generally doesn’t seem to make people feel better!) than the Andrews and Thomson view.

The other thing that struck me about the Andrews and Thomson paper, and to a lesser extent, Lehrer’s article, is that the focus is (intentionally) squarely on whether and why depression is adaptive from an evolutionary standpoint. But it’s not clear that the average person suffering from depression really cares, or should care, about whether their depression exists for some distant evolutionary reason. What’s much more germane to someone suffering from depression is whether their depression is actually increasing their quality of life, and in that respect, it’s pretty difficult to make a positive case. The argument that rumination is adaptive because it helps you solve complex analytical problems is only compelling if you think that those problems are really worth mulling over deeply in the first place. For most of the things that depressed people tend to ruminate over (most of which aren’t life-changing decisions, but trivial things like whether your co-workers hate you because of the unfashionable shirt you wore to work yesterday), that just doesn’t seem to be the case. So the argument becomes circular: rumination helps you solve problems that a happier person probably wouldn’t have been bothered by in the first place. Now, that isn’t to say that there aren’t some very specific environments in which depression might still be adaptive today; it’s just that there don’t seem to be very many of them. If you look at the data, it’s quite clear that, on average, depression has very negative effects. People lose friends, jobs, and the joy of life because of their depression; it’s hard to see what monumental problem-solving insight could possibly compensate for that in most cases. By way of analogy, saying that depression is adaptive because it promotes rumination seems kind of like saying that cigarettes serve an adaptive purpose because they make nicotine withdrawal go away. Well, maybe. But wouldn’t you rather not have the withdrawal symptoms to begin with?

To be clear, I’m not suggesting that we should view depression solely in pathological terms, and should entirely write off the possibility that there are some potentially adaptive aspects to depression (or personality traits that go along with it). Rather, the point is that, if you’re suffering from depression, it’s not clear what good it’ll do you to learn that some of your ancestors may have benefited from their depressive natures. (By the same token, you wouldn’t expect a person suffering from sickle-cell anemia to gain much comfort from learning that they carry two copies of a mutation that, in a heterozygous carrier, would confer a strong resistance to malaria.) Conversely, there’s a very real danger here, in the sense that, if Andrews and Thomson are wrong about rumination being adaptive, they might be telling people it’s OK to ruminate when in fact excessive rumination could be encouraging further depression. My sense is that that’s actually the received wisdom right now (i.e., much of cognitive-behavioral therapy is focused on getting depressed individuals to recognize their ruminative cycles and break out of them). So the concern is that too much publicity might be a bad thing in this case, and, far from heralding the arrival of a new perspective on the conceptualization and treatment of depression, may actually be hurting some people. Ultimately, of course, it’s an empirical matter, and certainly not one I have any conclusive answers to. But what I can quite confidently assert in the meantime is that the Lehrer article is an enjoyable read, so long as you read it with a healthy dose of skepticism.

ResearchBlogging.org
Andrews, P., & Thomson, J. (2009). The bright side of being blue: Depression as an adaptation for analyzing complex problems. Psychological Review, 116 (3), 620-654 DOI: 10.1037/a0016242

if natural selection goes, so does most everything else

Jerry Fodor and Massimo Piattelli-Palmarini have a new book out entitled What Darwin Got Wrong. The book hasto put it gentlynot been very well received (well, the creationists love it). Its central thesis is that natural selection fails as a mechanism for explaining observable differences between species, because there’s ultimately no way to conclusively determine whether a given trait was actively selected for, or if it’s just a free-rider that happened to be correlated with another trait that truly was selected for. For example, we can’t really know why polar bears are white: it could be that natural selection favored white fur because it allows the bears to blend into their surroundings better (presumably improving their hunting success), or it could be that bears with sharper teeth happen to have white fur, or that smaller, less energetic bears who need to eat less often tend to have white fur, or that a mutant population of polar bears who happened to be white also happened to have a resistance to some deadly disease that wiped out all non-white polar bears, or… you get the idea.

If this sounds like pretty silly reasoning to you, you’re not alone. Virtually all of the reviews (or at least, those written by actual scientists) have resoundingly panned Fodor and Piattelli-Palmarini for writing a book about evolution with very little apparent understanding of evolution. Since I haven’t read the book, and can’t claim much knowledge of evolutionary biology, I’m not going to weigh in with a substantive opinion, except to say that, based on the reviews I’ve read, along with an older article of Fodor’s that makes much the same argument, I don’t see any reason to disagree with the critics. The most elegant critique I’ve come across is Block and Kitcher’s review of the book in the Boston Review:

The basic problem, according to Fodor and Piattelli-Palmarini, is that the distinction between free-riders and what they ride on is “invisible to natural selection.” Thus stated, their objection is obscure because it relies on an unfortunate metaphor, introduced by Darwin. In explaining natural selection, the Origin frequently resorts to personification: “natural selection is daily and hourly scrutinising, throughout the world, every variation, even the slightest” (emphasis added). When they talk of distinctions that are “invisible” to selection, they continue this personification, treating selection as if it were an observer able to choose among finely graded possibilities. Central to their case is the thesis that Darwinian evolutionary theory must suppose that natural selection can make the same finely graded discriminations available to a human (or divine?) observer.

Neither Darwin, nor any of his successors, believes in the literal scrutiny of variations. Natural selection, soberly presented, is about differential success in leaving descendants. If a variant trait (say, a long neck or reduced forelimbs) causes its bearer to have a greater number of offspring, and if the variant is heritable, then the proportion of organisms with the variant trait will increase in subsequent generations. To say that there is “selection for” a trait is thus to make a causal claim: having the trait causes greater reproductive success.

Causal claims are of course familiar in all sorts of fields. Doctors discover that obesity causes increased risk of cardiac disease; atmospheric scientists find out that various types of pollutants cause higher rates of global warming; political scientists argue that party identification is an important cause of voting behavior. In each of these fields, the causes have correlates: that is why causation is so hard to pin down. If Fodor and Piattelli-Palmarini believe that this sort of causal talk is “conceptually flawed” or “incoherent,” then they have a much larger opponent then Darwinism: their critique will sweep away much empirical inquiry.

This really seems to me to get at the essence of the claim, and why it’s silly. Fodor and Piattelli-Palmarini are essentially claiming that natural selection is bunk because you can never be absolutely sure that natural selection operated on the trait you think it operated on. But scientists don’t require absolute certainty to hold certain beliefs about the way the world works; we just require that those beliefs seem somewhat more plausible than other available alternatives. If you take absolute certainty as a necessary criterion for causal inference, you can’t do any kind of science, period.

It’s not just evolutionary biology that suffers; if you held psychologists to the same standards, for example, we’d be in just as much trouble, because there’s always some potential confound that might explain away a putative relation between an experimental manipulation and a behavioral difference. If nothing else, you can always blame sampling error: you might think that giving your subjects 200 mg of caffeine was what caused them to have to go to the bathroom every fifteen minutes report decreased levels of subjective fatigue, but maybe you just happened to pick a particularly sleep-deprived control group. That’s surely no less plausible an explanation than some of the alternative accounts for the whiteness of the polar bear suggested above. But if you take this type of argument seriously, you can pretty much throw any type of causal inference (and hence, most science) out the window. So it’s hardly surprising that Fodor and Piattelli-Palmarini’s new book hasn’t received a particularly warm reception. Most of the critics are under the impression that science is a pretty valuable enterprise, and seems to work reasonably well most of the time, despite the rampant uncertainty that surrounds most causal inferences.

Lest you think there must be some subtlety to Fodor’s argument the critics have missed, or that there’s some knee-jerk defensiveness going on on the part of, well, damned near every biologist who’s cared to comment, I leave you with this gem, from a Salon interview with Fodor (via Jerry Coyne):

Creationism isn’t the only doctrine that’s heavily into post-hoc explanation. Darwinism is too. If a creature develops the capacity to spin a web, you could tell a story of why spinning a web was good in the context of evolution. That is why you should be as suspicious of Darwinism as of creationism. They have spurious consequence in common. And that should be enough to make you worry about either account.

I guess if you really believed that every story you could come up with about web-spinning was just as good as any other, and that there was no way to discriminate between them empirically (a notion Coyne debunks), this might seem reasonable. But then, you can always make up just-so stories to fit any set of facts. If you don’t allow for the fact that some stories have better evidential support than others, you indeed have no way to discriminate creationism from science. But I think it’s a sad day if Jerry Fodor–who’s made several seminal contributions to cognitive science and the philosophy of science–really believes that.

elsewhere on the internets…

Some stuff I’ve found interesting in the last week or two:

Nicholas Felton released his annual report of… himself. It’s a personal annual report on Felton, as seen through the eyes of a bunch of friends, family, and strangers:

Each day in 2009, I asked every person with whom I had a meaningful encounter to submit a record of this meeting through an online survey. These reports form the heart of the 2009 Annual Report. From parents to old friends, to people I met for the first time, to my dentist… any time I felt that someone had discerned enough of my personality and activities, they were given a card with a URL and unique number to record their experience.

You probably don’t much care about Nicholas Felton’s relationships, moods, or diet, but it’s a neat idea that’s really well executed. And it looks great [via Flowing Data].

Hackademe is a serialized novel about a man, with an axe, who dislikes professors enough to take them out behind the wood shed and… alright, no, it’s actually “a website devoted to sharing clever uses of technology, software, or modified items to solve problems related to information overload, time management, organization, productivity, and other challenges faced by academics on a daily basis.” Which is pretty cool, except that I have trouble seeing the word “hackademic” in a positive light…

The UK’s General Medical Council finally laid the smack down on the ethically-challenged Andrew Wakefield–he of “vaccines cause autism, and here’s a terrible and possibly fraudulent study to prove it” fame. There’s a very long but very good write-up of the whole debacle here. Unfortunately, the reprimand is really just symbolic at this point, because Wakefield now lives in the US, and isn’t (officially) practicing medicine any more. Instead, he spends his days pumping autistic children full of laxatives. I wish I were joking.

The Neuroskeptic has had a string of great posts in the last couple of weeks. I particularly enjoyed this one, wherein he exposes reveals himself to be an expert on all matters sexual, dopaminergic, and British.

According to a study in Nature, running barefoot may be better for our feet than running in shoes. Turns out that barefoot runners strike the ground with the middle or ball of the foot, greatly reducing the force of impact. This may explain why so many (shod) runners get injured every year, and is supposed to make sense to you if you’re one of those evolutionist folks who think humans evolved to run long distances over the course of millions of years. But since you and I both know god created shoes around the same time he was borrowing Adam’s ribs, we can dispense with that sort of silliness.

The Census Bureau has some ‘splaining to do. Over at Freakonomics, Justin Wolfers discusses a new paper that uncovers massive (and inadvertent) problems with large chunks of census data. The fact that the census bureau screwed up isn’t terribly surprising (though it does call a number of published findings into question); everyone who works with data makes mistakes now and then, and the Census Bureau works with most data than most people. What is surprising is that Census has apparently refused to correct the problem, which is going to leave a lot of people hanging.

Slime mold has evolved the capacity to plan metropolitan transit systems! So claims a study in last week’s issue of Science. Ok, that’s not exactly what the article shows. What Tero et al. do show is that slime mold naturally forms networks that have a structure with comparable efficiency to the Tokyo rail system. Which, if you think about it, kind of does mean that slime mold has the capacity to plan metropolitan transit systems.

Projection Point is a neat website that measures something its creators term your “Risk Intelligence Quotient”. What’s interesting is that the site measures meta-cognitive judgments about risk rather than risk attitudes. In other words, it measures how much you know about how much you know, rather than how much you know. If that sounds confusing, spend 5 minutes answering 50 questions, and all will be made clear.

Pete Warden wants to divide up the US into 7 distinct chunks. Or at least, he wants to tell you how FaceBook thinks the US should be divided up, based on social connections between people in different geographic locations. There’s Stayathomia, Mormonia, and Socialistan. (Names have been deliberately altered to protect the guilty states.)

Each day in 2009, I asked every person with whom I had a meaningful encounter to submit a record of this meeting through an online survey. These reports form the heart of the 2009 Annual Report. From parents to old friends, to people I met for the first time, to my dentist… any time I felt that someone had discerned enough of my personality and activities, they were given a card with a URL and unique number to record their experience.