• Evolutionary psychology questions answered, Part 2

    Back in December I asked readers to submit questions and promised to answer at least the top five (by votes).

    Science denialism at a skeptic conference
    Q&A Part 1: Confirmed & disconfirmed hypotheses

    This part’s question is from Tim McCollough.

     P. Z. Myers has equated EP with adaptationism and that it ignores other mechanisms of evolution. Does EP rely overly on adaptationism?

    I am going to assume that Tim’s question is not a distortion of the position of P.Z. Myers [EDIT: Tim has said in the comments that his question is not a just summary, so take my reply as a reply to his formulation and not necessarily to Myers’s writing]. I do not read his blog, and I will not now, because his immediate response to my critique of Rebecca Watson’s talk was to insult me personally and to disparage my motives. Such behavior disqualifies anyone from my attention when it comes to serious academic discussion.

    Much like deniers of climate change, evolutionary psychology denialists rehash tired old arguments which have been effectively dispatched over and over again. For example, read the short rebuttal from the Center for Evolutionary Psychology (CEP) here, or read a fascinating 1996 exchange between Steven Pinker et al. versus Stephen Jay Gould here (pdf).

    The CEP notes that even in 1966, influential luminaries like George C. Williams knew better, and wrote so:

    Evolutionary adaptation is a special and onerous concept that should not be used unnecessarily, and an effect should not be called a function unless it is clearly produced by design and not by chance. When recognized, adaptation should be attributed to no higher a level of organization than is demanded by the evidence.

    I have a peer-reviewed paper in the current edition of the journal Quarterly Review of Biology in which my co-authors and I review the arguments against adapationism before testing a specific adaptationist hypothesis and presenting evidence that does not support it. One of my co-authors on that paper is Elliott Sober, a distinguished philosopher of biology who has written extensively about the epistemology of evolution and about adaptationism (Elliott has many great books and papers; I would recommend Evidence and Evolution and Philosophy of Biology). So I am versed in criticism of adaptationism— I am one of its published critics.

    The question Tim raises is a weak criticism because it includes as premise the idea that “other mechanisms” can explain the ultimate origins of mind features that we study. To say that evolutionary psychology is over relying on adaptationism is like saying that walking overly relies on legs. In Part 1, I reviewed some of the fruits of adapatationism. I would invite P.Z. Myers or anyone to produce a similar list, reviewing the findings of ultimate causes of mind features from non-adaptationist mechanisms. I think that we would all be very interested in seeing that.

    When it comes to explaining how life on Earth started and then diverged into current forms, adaptationism is the only game in town. No biologist has proposed a coherent alternative hypothesis to natural selection in which the origin of the complex functional features of living things can be explained. It is not that evolutionary psychologists (or biologists) ignore other mechanisms of evolution, or more insultingly, that we just have not heard about them— it’s that they are not useful in finding answers to our questions.

    Non-selection processes
    I do not read the blog of P.Z. Myers, so I do not know which he spends time on. I will discuss genetic drift and happenstance. Wiki genetic drift if needed, I will not explain the definition here. Drift can have a huge effect on the frequency of an allele in a population, which is the most basic definition of evolution. That said, we still always need to understand the effects of natural selection in order for any postulated drift scenario to make sense. For example, the Pennsylvania Dutch exemplify the founder effect. A small, reproductively isolated group in which the descendants reflect the particular genetic hand of the founders and not a more diverse population. As a result, recessive genetic disorders are much more common among some populations therein, such as polydactyly, having an extra digit or digits. One must understand the founder effect to explain such phenomena, as well as more mundane features such as specific frequencies of hair or eye color in that population.

    Drift is not possible unless selection is absent. So even at the start, we have to think about possible selective pressures. Recessive disorders that result in sterility or young mortality will be filtered out quickly. Genes that significantly impact reproductive success will also be filtered over time. Next, drift hasn’t told us anything about where those alleles came from or why they were present in the original population to begin with. Drift might tell us about the frequency of brown hair in contemporary populations of the Pennsylvania Dutch, but not why the trait brown hair evolved, not why hair itself had evolved. Drift just does not explain the origins of design features. We will always need mutation and selection for that. Drift can tell us about bottlenecks, instances where genetic variation can sharply decrease. In other words, it can sometimes inform us what the stage upon which adaptation acts looks like. That’s important and evolutionary psychologists know this and generally include it in their considerations. Indignant reminders add nothing to the science, and I would invite P.Z. Myers or anyone else to prove otherwise.

    Happenstance
    Random events and conditions are significant in determining the course of evolution, and no evolutionary psychologist would deny it. The asteroid that ended the reign of most dinosaurs almost surely permitted the rise of the mammals, including ourselves. The first animals to reach and colonize the geologically young Galapagos Islands had no predators to fear or adapt to, making them behaviorally different from mainland cousins or hypothetical versions of themselves that could have landed on older lands that do have predators. These events are part of the ecology in which selection pressures are considered. They are part (where appropriate) of any good adaptationist account.

    There are smaller random events, as well, of course. A positive mutation arises, but by the nature of mutations only one individual has it. That person can randomly die or fail to reproduce because a beneficial mutation is not a guarantee of success, only a statistical improvement. Perhaps some genes are like Betamax versus VHS, where the superior version fails to catch on. This is all interesting, but it doesn’t help us understand evolutionary changes that do happen and why. As with drift, happenstance events tell us about the ecological world in which selection can act. It isn’t helpful understanding that mammals took over former niches held by dinosaurs without understanding how selection caused those animals to adapt to those new niches and subsequently interact in new ecologies.

    What if, by random accident, Elvis’s parents never met and he had never been born. This would surely have changed the history of rock music as we know it. Perhaps this did happen, but with respect to some other musical person who we don’t know because they were never born. Now I ask you, what does this thought exercise gain us? Do we understand how rock music grew and changed any better or why? Is there any real insight offered? Land animals would never have existed if the Earth (by random chance) happened not to have any dry land. Dry land is a random-factor “cause” of the evolution of land animals. Does this observation help us understand the evolution of land animals? With our hypothetical what-if ideas in hand, can useful hypotheses now be generated and investigated which could not have been otherwise? I do not aim at knowing what might happen but did not, but at knowing what did happen and why.

    Stay tuned for questions 3 & 4 in the next part:
    Evolutionary psychology is an inter-disciplinary study so you have to rely on evidence derived from anthropology, psychology, ecology etc. What problems can arise from this situation?    5 votes. Submitted by Chas Stewart.

    What, in your opinion, is the most surprising or unintuitive result evolutionary psychology has provided, and what is the evidence for it?   6 votes. Submitted by qbsmd.

    Category: Evolutionary Psychology

  • Article by: Edward Clint

    Ed Clint is a bioanthropology graduate student at UCLA, cofounder of Skeptic Ink, and USAF veteran.

    One Pingback/Trackback

    • I blogged last week, that Ed, RW, and, oh, say, Greta C. (or maybe PZ!) should take a trip to some netherworld together and re-enact No Exit. I’ve already put Ed in my Pop Ev Psych file, in general. Even should he be right on this particular issue, he’s not, in general: http://socraticgadfly.blogspot.com/2013/02/men-women-sexual-objectification.html

      • If you have any criticism to offer regarding anything I have said in this space, feel free to say so. There isn’t much that is helpful about vague assertions of “general” wrongness.

    • I had hoped you had read Meyer’s post, because I don’t think my one sentence question was fair to either you or Meyers. He first starts out on a long derail of the various forms of evolution. This derail will serve as quite a quote mine for the creationist since PZ spends paragraphs describe just how hard it is for a mutation to become fixed in a population. After the derail, he gives his core critique:

      “Now you can see that the first problem the evolutionary psychologists
      have to confront is whether the feature they are examining is actually a
      functional adaptation; they can’t simply assume that it is, as they
      often do, and then proceed on their merry way, building hypotheses to
      explain an assertion that they haven’t yet established as true.

      Wait, check that. Actually, the first thing they have to do is show
      that the feature they’re examining is a direct product of a genetic
      variant in the first place, and shows some pattern of inheritance. They
      often skip this step, too.”

      He promised more critique but has not done so since this posting.
      .He actually provides no evidence that EP is guilty of this, he merely asserts it. I guess he thinks that the long derail on population genetics would anesthetize the reader from noticing that he didn’t actually make an argument.

      I urge you to read this posting. If this is the only PZ post you read this year, then you will realize he is shooting blanks

      http://freethoughtblogs.com/pharyngula/2012/12/10/ep-the-fundamental-failure-of-the-evolutionary-psychology-premise/

      • It seems to me unfair to people who have questions and comport themselves with maturity and respect to give them the same or lesser attention than is given P.Z. Myers and his blog. I would have liked to have been able to have a good, civil debate with P.Z. (or another science professional) but P.Z. decided immediately that that was not what he wanted.

    • Minor mistake:

      “where the inferior version fails to catch on.”

    • As a linguist who focused on semantics and philosophy of
      science as an undergrad, there’s an issue in philosophy that jumps right out at
      me whenever this sort of criticism of “adaptationism” is raised. That is the
      fact that any state of affairs can be accurately described by an infinity of
      propositions.

      Are stepparents more likely than biological parents (i) “to
      physically abuse children”, or (ii) “to physically abuse children iff the temperature
      is between -90⁰C and 90⁰C”? Anything that we’re willing to call an adaptive
      feature can also be accurately described in ways like (ii) that we won’t want to call adaptive features, but this difference is just a fact about how
      our minds project counterfactual worlds.

      The foolishness of formulations like
      (ii) is apparent, but it helps us to appreciate the key point that natural
      selection doesn’t operate over semantic categories in any human language, nor
      over nonlinguistic categories in human cognition. Rather, differential selection of
      replicating patterns operates over everything that exists, simultaneously,
      without regard for any particular categorizations that some mind or language
      might come along to identify.

      So when we talk about an “adaptation”, we’re
      talking about a useful generalization within our shared system of classifying
      the world, not something objectively carved out from the fabric of differential
      reproduction. And, as Ed detailed in the last post, EP has produced very many
      good generalizations whose empirical predictions have stood up well.

    • kiiski

      Good post, one quibble: “Drift is not possible unless selection is absent”- it’s probably better to view it as an interaction between the processes, with drift increasingly important the smaller the population size, rather than two exclusive processes. Both can operate at the same time (example: the fixation of deleterious alleles in small populations)

      • That’s a fair point, but I hope the examples that I gave help to clarify that as well.

        • Dharlette

          I also really very strongly disagree with that statement; it shows a fundamental lack of understanding of what genetic drift is. There can be strong selection in favor of a trait, and an entirely unrelated threat can still kill an organism, thereby decreasing the frequency of an already rare allele in a population. What this means is that it is often very difficult for new traits to become fixed in a population, even if they are beneficial, and that rare traits tend to disappear over time.

          It’s quite disappointing that you were unwilling to so much as read his blog post just because he rose to the defense of a woman who was being harassed by leaders in the atheist movement. To be frank, it loses you a lot of credibility in my eyes, as it’s clear you weren’t addressing the actual concern here, which is that EP often assumes that every trait is an adaptation, when frequently it’s just learned behavior. Certainly, the impulses behind the learned behavior may be adaptations (for example, agreeing with people in leadership positions could certainly be a beneficial trait), but the ways in which this expresses itself in modern society might not have anything to do with the conditions under which it was adapted. For example, let’s say a leader in your community (let’s call him Richard Dawkins) denounces a particular human female (let’s call her Rebecca Watson), our hypothetical adaptation of agreeing with leaders might lead individuals to send her rape threats. That does not mean that the sending of rape threats is an adaptive trait in and of itself, it is (in this hypothetical example) an expression of a different trait that has nothing inherently to do with threatening women who speak their mind.

          • PZ Meyers went into excruciating detail about how hard it is for an advantageous mutation to become fixed in a population. So much so that his posting will serve as an excellent quote mine for creationists. But in the blog post I referred to he merely asserts that EP assumes adaptationist explanations for traits and proceed from there. He should have spent his time in that post actually giving evidence for that assertion. You merely repeat PZs assertion with no evidence and then throw in a reference to Dear Muslima for what purpose other than to stir shit up.

            • Dharlette

              Yes, I repeated PZ’s assertion because Edward Clint did not address the fundamental criticism: before you can explain why you think a trait evolved, you need to show that it has, indeed, evolved. There needs to be at least some basic evidence that the trait could be subject to natural selection (i.e., the trait needs to show variation, inheritability, selection, and plenty of time for it to have changed). This ought to be considered a pre-requisite to evo-psych, and all too often it is not.

              I wouldn’t have thrown in the Elevatorgate reference if Edward Clint didn’t start out his post by referencing it himself; as an aside, Rebecca Watson and how she is treated is oftentimes used as a litmus test by female skeptics & biologists for “do these people treat women as equals?” IF people go out of their way to make negative comments about her, then I start seeing some serious red flags.

            • I have made no reference to Elevatorgate in this writing.

            • Dharlette

              You’re correct; I was referring to the statement “I do not read his blog, and I will not now, because his immediate response to my critique of Rebecca Watson’s talk was to insult me personally and to disparage my motives.” Having done a bit more reading of your site, however, it’s clear that this refers to a talk against evo-psych that she gave after Elevatorgate and your defense against it. I can’t say I’m categorically opposed to an individual defending their field of research after an attack on it, so I can’t truly condemn you for writing that post and am sorry that those words immediately made me feel hostile towards you, but it is worth noting that my reaction here is not unusual. Generally speaking, when people choose to go after Rebecca Watson they’re signaling something very specific about themselves and their worldview. People are likely to interpret that signal in a quite specific way, which may make many people (particularly women) immediately feel hostile.

              I am quite confused by your previous post, in which you say “A trait can be advantageous and its allele(s) can then go to fixation. This means the variation is zero and the heritability is also zero.” Natural selection cannot work on a trait that isn’t inheritable. That’s a basic prerequisite. A trait that is fixed in the population is still inherited. Pretty much all humans have two eyes (there’s no variation there) but it is still a heritable trait. The important thing here is that a trait was variable when it was under selection. Now that it’s fixed, it’s no longer evolving.

            • When it comes to science, I make an effort to be as objective as I can. You are correct that Watson has been/is amid a storm of criticisms and harassment. However, being targeted unfairly does not mean that what you say is beyond legitimate criticism. If we can not separate the factual from the political, then we can not undertake any discussion of science.

              re: heritability. The technical biology definition is different from the vernacular. The definition of heritability is the proportion of the individual variation caused by genetics. Here is a discussion of why and why it matters: http://www.anth.ucsb.edu/projects/human/epfaq/heritability.html

            • “Generally speaking, when people choose to go after Rebecca Watson they’re signaling something very specific about themselves and their worldview. People are likely to interpret that signal in a quite specific way, which may make many people (particularly women) immediately feel hostile.”

              Do you really fail to see what’s so dangerous in this way of thinking about people and ideas?

            • “the trait needs to show variation, inheritability, selection, and plenty of time for it to have changed”

              You are quite wrong. A trait can be advantageous and its allele(s) can then go to fixation. This means the variation is zero and the heritability is also zero. Selection also doesn’t necessarily prove anything- selection today proves what is selected for today, not in the past. Insomuch as the present is indicative of the past, there is value there, but it is hardly required to be demonstrated. Demonstrate for me that the first bird was a decent glider by showing that gliding is a trait that is currently selected-for.

              There does need to have been time, but that’s fine since the evolutionary time frame we’re working with is 3.6 billion years. That is the length of time selection processes have been acting on our ancestors.

            • kiiski

              regarding litmus tests: As a female biologist I propose a Watson litmus test in the other direction: are people willing to excuse bullshit from her because she’s a woman and under attack, or will they criticize her ideas fairly, but even harshly, if need be? Isn’t the latter much closer to “treating women as equals”? (I don’t mean to pile on, since you’ve already admitted your first posts were a gut reaction; just putting a different perspective out there.)

            • Dharlette

              You’re missing the point here. It’s not that Watson is above criticism. It’s that she’s just a female blogger who talks about science and skepticism. The level of obsession that people have when it comes to criticising her is just strange. It’s not like plenty of other people haven’t criticized EP with pretty much the exact same arguments; EP is mocked pretty regularly in scientific circles. Watson isn’t anywhere near as giant a jerk as PZ Myers or Richard Dawkins, for example, but neither PZ nor Dawkins get anywhere near the level of death/rape threats that Watson does. It’s not about what she’s saying; lots of other people say the exact same thing. It’s about the fact that she says it while female, and that gets a freakishly disproportionate response out of people.

            • kiiski

              I explicitly said I was only describing a different perspective from yours, and that’s “missing the point”? Do you have any idea how arrogant that sounds? (PZ has long received death threats and the hate mail Dawkins gets is legendary, so I would question that assertion as well)

              However, I didn’t intend to start a further argument about personal drama, since Ed wanted this thread to be about the science. Sorry about that. But since assertions have been made about how many women feel, I felt it was relevant to describe why a woman might appreciate the approach Ed has taken here. That’s all.

            • Dharlette

              I don’t speak for all women, I only speak for me. Sorry if I sounded like I was.

            • Can you provide a link to a talk or discussion by someone else who makes as many misleading and false points about the subject of EV as Rebecca who then goes on to receive less critique?

              (I tried listing some problems with her talk that Ed had missed on a blog of my own, but it is proving quite a task and I have yet to find time to finish – http://psych0drama.blogspot.co.uk/ )

              Rebecca’s position as a women and/or a feminist does not mean that every criticism of her is motivated by disdain for women and/or feminists. Sometimes she is flat out wrong. Her talk on EV is a non-stop catalogue of error, and it is reasonable enough to point out that she talks balderdash when she does so.

              If a certain proportion of her critics is motivated by such disdain, by all means criticise them in turn.

              But don’t project concerns such as “you just criticise her because she is a women” onto all of her critics just because of the probable motives of some of them.

            • People complained my critique was as long as it was. Prior to posting, I deleted a section which at the time had 2-3 pages. I knew that I could have gone on pulling apart various points for many, many pages and that it would then take too long and would have been nearly a book-length writing. Still, you found some issues I had not noticed. Kudos.

            • Dharlette

              I can give you plenty of examples of critiques of EP, but if you’re only interested in ones that are full of errors then maybe the motivation here is that Watson is simply a convenient straw-man for you to attack instead of addressing the real issues? Regardless, I’m tired of this conversation. I think we’ve all said our piece here, I don’t think anyone has changed or is going to change their minds farther than they already have, and frankly I would rather Edward Clint spend his time addressing the criticisms I’ve put forth of one of the papers he set up as a “proven” and uncontroversial example of EP (i.e., not a strawman, since the attacking of strawmen is one of his major criticisms of Watson).

            • Rebecca might constitute something of a strawman in that her arguments are easy to demonstrate as false or irrelevant, but that does not mean that to criticise her is attacking a strawman in the philosophical sense. She does actually say what she says (and has doubled down on some of the things she was criticised for).
              The classical strawman, as I understand it, is to ignore what someone says and instead argue with something superficially similar that also happens to be easily refutable.
              But that’s not the case here.
              As for whether or not Rebecca attacks strawmen, I would say it’s hard to tell, because she seems to veer from target to target without any coherence. In places she certainly does though. Her “summary of evolutionary psychology” is a classic strawman.

          • “There can be strong selection in favor of a trait, and an entirely unrelated threat can still kill an organism”

            Super. So that would tell us why a hypothetical mutation failed to proliferate in one specific situation. What does it tell us about the ones that didn’t, ones in other circumstances?

            As for the rest of this, I can understand why you’re disappointed with my site. Perhaps you’d be more comfortable at a more political/commentary site instead. Let’s keep this section about evolutionary psychology and not internecine secular politics.

            • Dharlette

              I apologize for using the vernacular definition of “heritability”; however, in this particular instance it works for me, as the definition of “inheritable” that is in question when talking about VIST is Darwin’s: which is to say, that a trait can be passed on from parent to offspring, not the proportion of individual variation caused by genetics. So, while I used a vernacular term here, I was indeed using the correct definition for the case at hand, and my criticism still stands.

              I stand by what I’ve said about Watson, which is as follows: I was wrong to judge you so quickly, but correct to point out that you sent a very specific signal that would normally be interpreted exactly the way I did. What you did is essentially the equivalent of a congressman talking about the “sanctity of marriage.” They may not say the word “gay,” but you know what they’re telling you is that they’re opposed to gay marriage. Now, this is problematic, because it means that anyone who actually wants to talk about the sanctity of marriage is likely to get mistaken for homophobic, but the person to blame for that interpretation isn’t the listener, it’s all the people who have made that phrase mean something different. It’s completely unfair to you that you can’t talk about Watson in a negative sense without being mistaken for misogynist, but thanks to the actions of lots of *actual* misogynists that’s what happened.

              And lastly, I don’t think it’s appropriate for you to tell me to wander off to a politics site. I’ve been reasonable for the most part, with the exception of some belligerence in my early posts (which I already apologized for). I’ve given citations, I’ve made logical arguments, and I’ve avoided fallacies or straw-manning you. All in all I’ve been well within bounds of acceptable behavior for internet commentators, and I do not appreciate being told to run off and play at the social sciences.

            • “It’s completely unfair to you that you can’t talk about Watson in a negative sense without being mistaken for misogynist, but thanks to the actions of lots of *actual* misogynists that’s what happened.”

              That’s not what happened to me when I read his piece, nor to a whole lot of other people. If that’s what happened to you, then it’s not his job to sort out your own cognitive malfunctions.

              You’re using precisely the same tactics of emotional intimidation that Jews and Muslims often use against liberal atheists in order to deflect criticism of their awful scriptures, histories and traditions. I don’t doubt that a moderate Muslim, who has experienced unjust bigotry throughout their life, might have an immediate emotional reaction that connects any of our arguments against the Quran to those painful experiences. But, as understandable as such a reaction might be, it’s not rational or commendable.

              In the same way, no amount of terrible sexism in the world provides a legitimate defense of Watson’s wildly inaccurate, reference-free put-up-job of a talk.

            • Dharlette

              Well, I’ve found that attacking people’s religions usually doesn’t get you very far, to be honest. As an atheist I’ve had great success arguing against specific beliefs that are religiously informed, but I’ve never convinced someone to give up their faith. Attacking people is usually something you do when you’ve already written them off; it doesn’t accomplish much besides allow you the pleasure of being snarky. (As an aside, that’s pretty much my main complaint against PZ Myers, whose opinions I almost always agree with but who seldom shares them in an effective way). Feeling offended isn’t “emotional intimidation,” it’s a thing that happens when your fundamental beliefs are questioned in a belligerent way. Feeling offended is why I was hostile here, it’s probably why PZ Myers wrote such a nasty rebuke of Ed Clint (based on what he read, I’m guessing he took Edward’s piece as signalling the same thing i did), and it’s probably why Edward Clint wrote the piece in the first place: his whole field of study was under attack.

              The best way to convince a fundamentalist to stop persecuting gays and atheists? Read the bible, and then quote it at them. Not in a mean way, not in a nasty way, in a “this is what your god says about love” way.

            • re: heritability No need to apologize, the important part is that we understand each other. Fortunately, what I study has obvious heritability (in the vernacular sense). For example, my last paper is about spatial abilities that relate to navigation and wayfinding. This is a complicated bit of cognition which is closely associated with the hippocampus. To say there are no genes which influence spatial ability would be a preposterous statement on the face of it. It is also known that hormone levels at different developmental points (and instantaneously) can affect spatial abilities. Genes that influence theses levels would naturally be heritable. None of this is controversial.

              re: Watson
              I appreciate the apology and I think we can be glad that we understand each other a bit better. Frankly, I don’t want this site to be about topics like elevatorgate or Watson vs her critics etc.., those are fine subjects for discussion, but I’d rather stick to the science of ev psych, critical thinking, and secularism. I only addressed Watson’s talk because it was on Ev Psych, and then it was about the content of the talk and not anything personal, certainly nothing attempting to justify any nasty criticism or harassment. I only mentioned up PZ because it was part of Tim’s question.

              I did not mean to offend you re: going to a political site. Since you reminded me of the power of appearances, I will ask you to understand your own appearance to me: someone looking to grind political axes. Such a person will not be pleased to be here as it is not what they are looking for. I’m perfectly happy to discuss the ev psych with you, as we have been.

            • Dharlette

              Alright, I think we have both apologized to eachother at this point, so I’m going to move my discourse to the thread about spiders.

          • kiiski

            Hi Dharlette – although I disagreed with the way Ed put it, I think it’s clear from the context that he understands drift, and the crucial point is that drift does not explain the origin of functional traits. PZ’s broadside attack against EP is so indiscriminate that it actually succeeds in throwing suspicion against any adaptive explanation, as others have noted. For example, he asserts that traits that haven’t been completely eliminated, like color-blindness, are “invisible to selection”! This would mean, among other things, that one of the most famous examples of natural selection in action- industrial melanism in peppered moths- was not an example of adaptive evolution.

            • Dharlette

              I’m not following you here kiiski. I think what PZ means when he says that traits that haven’t been completely eliminated are “invisible to selection” is that in order for a trait to be selected against it has to be present in an individual’s phenotype, not just their genotype. Since colorblindness is rare and recessive, most people who carry the gene don’t present the trait (we only really see it in males where the lack of a second X chromosome makes them vulnerable to many X-linked genetic disorders). Ironically, this is one of the few areas where genetic drift can be stronger than natural selection, as it will likely eliminate rare genes regardless of whether they are actually expressed.

            • kiiski

              Recessive alleles are only invisible to selection as long as they’re so rare that the phenotype hardly appears – colorblindness, being X-linked and present in 5-8% of men, isn’t one of those traits. The recessive gene example actually shows the opposite of what PZ claims (that if a variant hasn’t been completely eliminated, it hasn’t been subject to “strong selection pressure”): it shows that even strong selection doesn’t necessarily eliminate a variant completely. And there is some disagreement on whether colorblindness is actually a disadvantage for humans. But either way, what does all this have to do with the probability of some psychological traits being adaptations?? It’s simply a red herring.

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