Is morality innate? A debate in the NYT book review

December 30, 2013 • 6:34 am

UPDATE/CORRECTION: I’ve heard via email from Paul Bloom, who sent me a correction that I requested permission to post.  Having gotten permission, I’m putting Bloom’s email below, and apologize if I misrepresented his argument (I was more or less riffing on a review of a book I hadn’t read—but will).

I enjoyed your discussion of JB on WEIT, but you end with this:
And the rapidity of such changes imply, contra Bloom, that many of our moral sentiments are not hard-wired.
This isn’t contra Bloom at all; I argue in considerable detail that many of our moral sentiments are not hard-wired, and actually give some of the same examples that you do. (Pinker’s new book had a big influence on me.) In fact, one main theme of the book is that our innate morality is tragically limited — we are, by nature, savage to strangers; an inclusive morality is the product of cultural innovation; it’s not in our genes.
_________________

In Sunday’s New York Times Book Review, University of Cambridge psychology professor Simon Baron-Cohen reviews Yale psychology professor Paul Bloom’s new book, That book, Just Babies: The Origins of Good and Evilcontends that much of human morality is innate, and therefore likely produced by natural selection. (That itself presumes, if morality is a genetic adaptation, that individuals with more “moral” feelings and actions left more descendants.) Baron-Cohen is highly critical of this view, for he sees the evidence as thin:

Is morality innate? In his new book, “Just Babies,” the psychologist Paul Bloom draws from his research at the Yale Infant Cognition Center to argue that “certain moral foundations are not acquired through learning. . . . They are instead the products of biological evolution.”

He describes a study in which 1-year-olds watched a puppet show where a ball is passed to a “nice” puppet (who passes it back) or to a “naughty” puppet (who steals it). Invited to reward or punish the puppets, children took treats away from the “naughty” one. These 1-year-olds seem to be making moral judgments, but is this an inborn ability? They have certainly had opportunities in the last 12 months to learn good from bad.

I suppose this depends on whether parents actually instruct children less than one year old in how to behave, and that’s an unknown, for of course children can pick up subliminal cues. Ideally, of course, the decisive experiment would be to bring up children without any instruction in “good” versus “bad” behavior, but that’s impossible as well as unethical. As Baron-Cohen notes:

Proving innateness requires much harder evidence — that the behavior has existed from Day 1, say, or that it has a clear genetic basis. Bloom presents no such evidence. His approach to establishing innateness is to argue from universalism: If a behavior occurs across cultures, then surely it can’t be the result of culture. An example he provides is that young children in many cultures expect to be treated fairly — they get upset, or even spiteful or vengeful, when faced with inequality. Supporting Bloom’s claim is the fact that similar behaviors can be seen in other species: Researchers report that a dog that gets a smaller share of a treat appears vexed. Dangers of anthropomorphism aside, this hints at nativism.

I’m not sure what Baron-Cohen is getting at with his accusations of “anthropomorphism” and “nativism,” for one can certainly observe wild animals—or captive animals that haven’t been “instructed” in morality—and see if they have behavior that appears to reflect a sense of “fairness.” Frans de Waal has written extensively about this, and made this video (which I’ve discussed before) of capuchin monkeys demonstrating what looks for all the world like a sense of fair play:

It’s hard to look at that and not agree with Darwin that some of our “moral sentiments” are present in our relatives.

I know others have criticized de Waal for relying largely on anecdotes to support his views of the evolution of specific moral judgments, and I’m not sufficiently familiar with the literature to evaluate this criticisms.  But those anecdotes seem to have added up to at least intriguing speculation that some of our innate moral feelings were inherited from common ancestors.

Baron-Cohen is, however, properly critical of other studies in humans cited by Bloom as evidence of innate morality, some of which seem dubious from the outset.

Baron-Cohen implies that morality is purely learned, and that its “universality” simply reflects simply cultural inheritance from and between human ancestral groups.  In that case its only “innateness” is the evolved ability of humans to learn from others.

But there is another possibility, one not explicitly discussed, but subsumable under Bloom’s notion that “moral foundations” are innate. This is the view that humans have an innate ability to learn morality—a “morality module” that differs from our simple ability to learn. Such a module would resemble the “language module”: our innate (and presumably adaptive) ability to learn languages and use syntax. In that case the ability itself is presumably genetic, but the specific language we learn depends on our culture.  Similarly, a “morality module” would reflect our ability to quickly grasp what is “right and wrong” in different societies, but would involve parts of the brain different from those involved in learning other language and other things. This might explain that although moral sentiments are universal, the particular sentiments differ widely among cultures.

I don’t find that idea completely satisfying, since in our primate relatives some moral feelings do seem innate—or at least unable to be taught. It’s hard to avoid feeling that tendencies toward preferential treatment of one’s children and group-mates as well as reciprocal altruism within small groups and wariness toward strangers, would be subject to direct selection in our ancestors. Nevertheless, much religiously-based “morality” is surely learned: I doubt that we’re born with an innate hatred of gays (remember “You’ve Got to Be Carefully Taught” from the musical South Pacific?) or an aversion to contraception.

I remain open about how many of our moral feelings and behaviors are “hard-wired” versus culturally inherited versus the combination encapsulated in the “moral module” I suggested above.  But there’s certainly no evidence to support Francis Collin’s suggestion of an innate “Moral Law” in all humans that was bestowed by God; for that presumes (leaving God aside), a morality that is not only universal, but inborn—i.e., genetic.

Baron-Cohen’s conclusion is a bit unsatisfying, for it’s bloody obvious:

But to the extent that we have an innate moral sense, he [Bloom] concludes, humans are not prisoners of it. We can use our capacity for reason to override our emotions, our inclinations toward racism or revenge. “We are more than just babies,” he writes. “A critical part of our morality — so much of what makes us human — emerges over the course of human history and individual development. It is the product of our compassion, our imagination and our magnificent capacity for reason.” This is an optimistic view of human nature. The sobering message for me is that our abhorrent, corrosive emotions like racism or revenge will inevitably resurface, so we will always need to be on guard.

All this says is that some people are good and others are bad, and that will always be so. Insofar as Baron-Cohen suggests that we have “free will” to override our emotions, I won’t have any part of that.  Yes, people can behave in ways that counter not only whatever morality has evolved, but also whatever morality is learned. But that doesn’t mean that such “overriding” is a choice.  It could result purely from deterministic effects of our genes and our environments.

Finally, Baron-Cohen is overly pessimistic, for I agree with Steve Pinker that some corrosive emotions (or at least behaviors) will eventually be gone for good, at least as social norms. Those include the feeling that it’s okay to have slaves and kill your unwanted children, as did the Spartans. Others, like discrimination against gays and women, are on the way out. Pinkers’ last book, The Better Angels of our Nature, describes the huge changes over the last five centuries in what has been considered moral (or at least appropriate) behavior—behavior towards other people, towards women, towards children, and towards animals. These changes have occurred far too rapidly to be explained by genetic evolution.

Contra Baron-Cohen, once these forms of discrimination are gone (granted, some individuals will always be homophobic and misogynistic), I suspect that we won’t see their widespread recurrence.  And the rapidity of such changes imply, contra Bloom, that many of our moral sentiments are not hard-wired.

55 thoughts on “Is morality innate? A debate in the NYT book review

  1. Having just read Steven Pinker’s account of the incredible cruelty and sadism in ancient times (The Better Angels of Our Nature), I find it hard to believe that morality is innate.

    1. I’d say of course morality is innate. That we have a genetically programmed moral system is about as obvious as the fact that we have a genetically programmed immune system.

      However, the genes give a recipe, and how that recipe plays out depends very much on the developmental environment.

      As Jerry says, the only sensible proposal is that an interplay of genetics and learning/environment produce the end result.

      1. “Proto-morality” may be the result of an innate hesitancy to react immediately or aggressively to unknown stimuli and the phenotype is interpreted as post hoc moral cooperation. Of course, from a pragmatic perspective, this is moral behavior if a negotiation is conferred (albeit unintended).

    2. But the cruelty and sadism in ancient times was all the worse because such actions purportedly had reasons behind them which allowed them to fit into the cultural rules. The people who performed the atrocities weren’t criminals. There were always justifications and explanations (explicit or implicit) for why acts (like torture) which would be repugnant if done in normal contexts where everything is right are fine and dandy in these circumstances.

      That points to a moral system. A bad one by our standards, sure, but not complete and total anarchy where anyone can do anything to anyone and there are no social consequences if you can physically get away with it. We are moral animals.

      And if people are justifying their actions, then those justifications can be attacked rationally. That’s what happened when small tribes began to interact in positive ways with other tribes which had different moral systems. They had to find a consensus in order to work together.

      1. Indeed, if one views the relationships of eusocial organisms (hive insects, mole rats, etc.) as a very rigid but elaborate and well-developed form of morality — and I don’t see how one can’t without invoking religious nonsense — then it becomes quite clear that all members of any species with any degree of sociality have some form of morality as well, and that each defines the other.

        With this perspective, suggesting that H. s. sapiens is somehow naturally utterly devoid of morality and moral instinct is as bizarre as suggesting that we’re not tetrapods.

        Cheers,

        b&

        1. Exactly. Look at the differences between group-dwelling species with social hierarchies and species which basically just lay their eggs and walk away.

          When religious people point to examples of societies which presumably had “no moral system” — like the Nazis and the Communists — they’re actually indicating moral systems which were very rigid, disciplined, closed, and authoritarian. Sort of like their ideal of a God-centered morality.

          1. Yup — the old Christian variation on the “Not Invented Here Syndrome.” Only, with Christians, the Christian variant is the only one that even exists. If your morals aren’t Christian, then you have no morality. If your love isn’t Christian, you have no love. If your marriage isn’t Christian, you aren’t actually married.

            Ultimately, I don’t know if there’s any meaningful response to that sort of parochial arrogance other than, “Fuck off, asshole.”

            Cheers,

            b&

        2. Hive insects are kin in most cases. I believe I read this in my Ridley book where worker ants are all sisters, honey bees are sterile and bumble bees have some different kin relationship and therefore don’t last as a hive and start over new each year. So really they are acting selfishly, which has a cooperative outcome.

          The same can be said for humans except our brains have capacity for empathy and such which lets us layer on more to instincts.

          1. …but I wonder if we really instinctively see it that way. We have the instinct to protect our genes. Morality layered on top of that may come through empathy which relies on brain development. Indeed, I recall being a lot tougher as a kid and I remember the toughness of my kid peers; probably why they make good child soldiers.

          2. Oh, certainly — as I noted earlier, as with anything else, our instincts only get us started…and the optimal solution is often decidedly contrary to what our instincts steer us towards. See also Darrelle’s commentary on motorcycle handling.

            b&

          3. Mirror neurons, fascinating. The same pattern of neural activity occurs in your brain in response to you experiencing something yourself as when you observe someone else experiencing the same thing.

          4. Yes, the mirror neurons are interesting and even birds have them. There is a lot of controversy as to what they are for but I’m sure they contribute to a theory of mind, whether that’s what gave their holder the advantage or not.

  2. Something is wrong with the beginning of this sentence, unless I’m mis-parsing: “All this is says is that ….”

  3. “Bloom’s implies that morality is purely learned, and that its “universality” simply reflects simply cultural inheritance from and between human ancestral groups.”

    Given what we have discovered and understand so far about complex systems in general, especially complex biological systems, I am surprised whenever an “expert” makes a claim like “morality is purely learned” or “morality is purely innate.” One thing that seems very clear is that minds are much more complex and messier than that.

    Though it is purely anectdotal, I am perfectly comfortable with stating that some clearly perceptable aspects of personality, that are long term and maybe permanent, are there at birth, and even before birth (my twins were 2 months premature). I can only guess that whoever came up with the idea of the blank slate either never had children or was a very unobservant, and likely poor, parent.

    1. I too can see that long term (presumably life-long) aspects of individual personality appear at a very young age in children. I am raising 3 of them right now, and they all have very different personalities. Parts of these individual personalities were evident as soon as they could crawl. I doubt very much that we installed their individual traits into a ‘blank slate’. The possible origins of these differences include genetics (including chromatin modeling), their uterine environment, and maybe an element in chance in how the brain gets wired as develops and grows.

      1. Yes. I think the answer to the “nature or nurture” quandry is clearly “both,” and that it is no longer an interesting or profound question. The interesting and much more difficult question is “to what degree (endlessly variable I’m sure) and how does each contribute to behavior (the processes occuring in the brain).”

        1. Darrelle
          What this seems to suggest, to me at least, is that both aspects, nature and nurture, are simply points on a continuum, and taken together, are consistent with and subsumed within the laws of conservation of energy.

  4. I reckon that definitions are essential in this debate if we want to avoid it spinning off into la la land.

    Firstly I think the ‘morality’ and ‘Moral Law’ are high level concepts – and like all high level concepts they need to be tested against the world of facts.

    Secondly, a lot of the high level concepts depend on culture and development for their underpinnings – which again need to be tested against the world of facts.

    Thirdly, I suspect there are many genetically influenced behaviours which underpin cultural learning. Such as favouring kin and kith (and apparently strangers) over known enemies. Such as protecting children. Such as wanting the ‘protection’ of social status. Such as alerting to agency, or placing greater emphasis over the near rather than the distant, and so on. These ‘moral primitives’ are innate – but they are contextual, automatic, and may not be consistent with each other.

    A grab bag of evolutionary moral primitives cannot be said to form a rational ‘Law’, but it might explain why many of the higher level concepts of ‘Moral Law’ have difficulty when faced with real life situations. Which is why ‘killing is wrong’ doesn’t sit well with a ‘justified war’ – both are elaborations on different moral primitives.

    1. Discussions like this almost always run afoul of definitions, and attempting to scientifically investigate such squishy terms usually runs into the same problems. I have to agree with you fiercely. The human mind is remarkably plastic in behavior, so I expect there to be plastic cultural influences on a more or less “hard wired” base, and the definitions make it very difficult to make a distinct learned/innate boundary since there is no clear moral/immoral boundary or test to establish such a boundary.

      I still remember being amazed that my son at less than one year old, with no real language skills at all, had a decent understanding of property and ownership, in that he felt entitled and reacted negatively to being denied certain toys and objects that did not have a lot to do with staying fed or being comfortable. He just wanted to have them in is possession, or have it made clear that they were not being taken away (leaving said object in plain view during activities inconvenient for him to be holding them for example).

      Even though there are a lot of learned behaviors I suspect humans operate in many very basic and predictable ways on a number of levels, much more than most people are comfortable with.

  5. Morality is based on abstract concepts. The notion of good and bad is a human creation.

    The behavior of primates shows that they possess a SOCIAL INSTINCT, which may result in kindness to members of the same group and the observance of certain innate rules (instinctive, not moral) to maintain social cohesion.

    A moral behavior, by our standards, is one that do not distinguish between friend and stranger, is the intent to do what is right, regardless of personal gain or peer pressure. The “righteousness” that some animals show towards members of the same group usually turns into agression towards different groups.

      1. You can go to your profile in wordpress.com and there you’ll find a way to upload an avatar of your choice, just like I did. I hope that helps, because there is nothing Jerry can do about it.

    1. I once read something somewhere in which someone reduced the Most Basic Moral Law to: Treat similar things in a similar way.

      As long as there is some sort of feeling of connection (similarity) between one person and another, then “fairness” and “unfairness” kicks in.

  6. The idea of fairness might be related to the “I’ll get mine” attitude necessary for survival. For example, litters of baby mammals such as dogs or mice repeatedly squirm and push each other out of the way to get a better share of the mother’s food, warmth, attention, and comfort. Individuals that can’t/won’t do that will weaken and die.

    Darrelle wrote that “some clearly perceptible aspects of personality, that are long term and maybe permanent, are there at birth”. I agree with this and am willing to extend it to domesticated animals like puppies and kittens.
    However, some parents either aren’t interested in their offspring’s personality or view it as a challenge to their authority, and judge their babies as “good” or “bad” from birth (crying is bad, smiling or lying still is good). My family did this but it was not rare at that time.

  7. Right now I’m reading Ridley’s
    The Origins of Virtue: Human Instincts and the Evolution of Cooperation and it spends a bit of time talking about preference for kin (as already mentioned by DiscoveredJoys above). It also talks about various experiments in game theory (prisoner’s dilemma, tit-for-tat, generous) and that whatever game we’re playing, if we know and trust the players, we are more successful. It also talks about our innate tendency toward tribalism (in and out groups) which we’ve all experienced as high up as nationality and as low down as various clubs we belong to. He references the Selfish Gene as well and concludes that our genes are acting selfishly and we are acting selfishly to protect the individual (with the exception of kin) even when we think we are protecting the group (we’re doing it to protect ourselves and our kin).

    So it would seem that we have the basis for morality built in though evolution and it’s to our advantage to treat those around us nicely and cooperatively but how that looks, relies on reason and culture (as evidenced by just how nasty we can be and have been – see many awful examples in Steven Pinker’s book as Stephen Barnard points out).

  8. Reading this, I am reminded of a videotaped interview I saw years ago. It is so long ago, perhaps it is an apocryphal memory; it doesn’t matter. I forget the players and the exact circumstance, but the interviewee was a concentration camp survivor who’d been called to testify against one of his tormentors at a war crime trial. At trial, the victim watched the defendant testify right before taking the stand. Moments into his testimony, the victim completely fell apart and had to be helped back to his seat.
    The interviewer asked about the incident and suggested that it was understandable for a person faced with such evil to find it unbearable.
    The victim immediately perked up and objected. He had expected to see a monster exposed in the testimony preceding his own, but instead he’d seen a fearful man not essentially different from himself. If his tormentor was a man like other men, then all men might have the capacity to commit the acts which the victim had witnessed. If all men might have the capacity to commit such acts, then so might the victim himself. That, he explained, was why he started screaming.
    We may be able to engineer our environment to make “corrosive emotions” and their associated behaviors less relevant. I don’t think we will ever be rid of them, or the need to be wary of them, especially on a personal level.

  9. If one understands morality as an effective strategy for societal success, then it’s not at all hard to compare our innate ability to on-the-fly perform the insanely complex calculus required to throw and catch things while running and jumping with a similar innate ability to do game theory calculus.

    Similarly, just as one will have certain instincts that give you a chance at playing ball in the first place, it takes a great deal of learning and practice to hone those instincts to achieve maximum effectiveness — and that often means doing things that are counter-intuitive or “unnatural.” Yet, with time the obvious superiority of those non-instinctual actions makes you wonder how it ever could have even occurred to you that it might be otherwise.

    Cheers,

    b&

    1. “. . . it takes a great deal of learning and practice to hone those instincts to achieve maximum effectiveness — and that often means doing things that are counter-intuitive or “unnatural.””

      My clearest, most visceral, experience of this was teaching myself a particular “skill” for motorcycle road racing. Actually it is useful for regular riding too of course.

      It just happens to be the case that when you are near the limits of a motorcycle’s performance (traction, stability, lean angle) and something bad happens, the worst possible thing you can do is the thing that a human does automatically by reaction. That instictive reaction is to make things stop, slow things down, by closing the throttle or even braking. As it turns out, in virtually every situation you can think of the best thing to do when an unexpected “event” occurs is to stay on the throttle, and in some cases open it more. Training yourself to overcome your natural reaction to what your body seems to be interpreting as a life threatening situation takes some practice. But modern life seems to be full of such situations.

  10. We have sociopaths and psychopaths in our populations – people who have never had a fully functional moral engine, despite constant training.

    How does Baron-Cohen explain Dexter?

  11. ” . . . I agree with Steve Pinker that some corrosive emotions (or at least behaviors) will eventually be gone for good, at least as social norms. Those include the feeling that it’s okay to have slaves and kill your unwanted children, as did the Spartans.”

    Speaking perhaps anecdotally, I know of at least one American conservative politico –

    (in a seeming attempt to justify the legitimacy and enshrinement of slavery in the U.S. constitution and to preserve the fatuous conceit of “American Exceptionalism”)

    – stating words to the effect that slavery in the U.S. for African slaves was better than the circumstances they would otherwise have had to endure had they remained in Africa –

    (African tribes selling other different African tribesfolk as slaves, etc., of course not mentioning European colonialism – i.e., those of you who don’t become our slaves where we live, we’ll impose ourselves on the remainder of you where you live)

    – as if that ought to be somehow consoling to the slave, and a rationalization in response to which the slave and his descendants must needs slap their foreheads and exclaim, “Duh! But of course!”

    No doubt a significant fraction of these politicos fancy themselves highly moral religiosos.

    1. Actually, the reasoning of the conservative is an improvement over the past because he’s justifying slavery as being better — in the long run and if you look at the big picture — for the slave.

      As disgusting as this is, it is still technically better (ie more compassionate) than justifying slavery without caring, in any significant way, about the feelings or future of the slave because they are more like cattle than they are like other people. When slaveholders in the United States began to try to frame themselves as benevolent caretakers for adult-children — as opposed to talking only about profit and blacks as sub-human stock — it was the beginning of the end. The Enlightenment is seeping in. Plus, testable claim.

  12. I just can’t understand how an innate basis for morality can even be questioned, as so many other behavioural attributes of animals can be traced back to a genetic basis. Why should a subset of behaviour, which we choose to classify as “moral” be exempt from having this genetic origin? Evolutionary Game Theory indicates the behavioural strategies that will become dominant and/or will stabilise in a population in prescribed situations, and we see these are identical to strategies become heritable in nature. For social animals game theory predicts reciprocity and altruism, so selection pressure exist for those behaviours. We measure these tendencies for reciprocity, altruism and fairness in other social animals, particularly primates. Complex as human culture is we build extensively on these innate behaviours to construct our complex moral systems, but it still doesn’t mean that an innate basis doesn’t exist.

  13. But there is another possibility, one not explicitly discussed, but subsumable under Bloom’s notion that “moral foundations” are innate. This is the view that humans have an innate ability to learn morality—a “morality module” that differs from our simple ability to learn. Such a module would resemble the “language module”: our innate (and presumably adaptive) ability to learn languages and use syntax.

    I also thought about a comparison to language — and see you got there.

    1. Although it’s worth adding that a growing number of linguists and psychologists are quite sceptical of the existence of such a language module, in the sense of an innate module devoted very specifically to language acquisition, for which serious evidence is actually somewhat scant. Many (like me) prefer to assume only that humans are “language-ready” in that the combination of a predisposition to communicate and a large brain with its particular (non-language-specific) biases and constraints leads to the emergence of conventional communication systems that are adapted to humans, rather than the other way round.

      1. Yes, which makes the comparison a better one I think, since the concept of a “morality module” sounds like something out of phrenology. We are ‘morality ready.’

  14. This is the view that humans have an innate ability to learn morality—a “morality module” that differs from our simple ability to learn. Such a module would resemble the “language module”: our innate (and presumably adaptive) ability to learn languages and use syntax.

    Marc Hauser’s book Moral Minds explores this analogy with language at great lengths. It also discusses interesting moral thought experiments involving trolleys. (For the record, Hauser was found guilty by Harvard of scientific misconduct.)

    Also, off topic, but Simon Baron-Cohen has a famous cousin and his work is sometimes quite ethically questionable.

  15. I would question the oft repeated claim, usually from religious apologists:

    OP “. . . Those include the feeling that it’s okay to have slaves and kill your unwanted children, as did the Spartans.”

    It is often claimed that the Spartans practised infanticide, even throwing such unwanted children into a chasm under the Greek mountain Taygetus. In 2007 archaeological digs in the area did not support the Greek myth that ancient Spartans threw their stunted and sickly newborns off a cliff. Theodoros Pitsios, Anthropologist at the Athens Faculty of Medicine says that after more than five years of analysis of human remains culled from the pit, also called an apothetes, researchers found only the remains of adolescents and adults between the ages of 18 and 35. The bones studied to date came from the fifth and sixth centuries BCE and are from 46 men, confirming the assertion from ancient sources that the Spartans threw prisoners, traitors or criminals into the pit.

    See the Australian ABC report “Study finds no evidence of discarded Spartan babies,” 11 December 2007.

    A similar claim is shown wrong in this article “Skeletal Remains from Punic Carthage Do Not Support Systematic Sacrifice of Infants,” 17 February 2010 in PLoS ONE 5(2): e9177. doi:10.1371/journal.pone.0009177 by Jeffrey H. Schwartz et al.

    This is not to deny that infanticide was often used as a form of very late abortion by primitive tribes. But I don’t think that you can lay this crime at the feet of a lack of religious belief.

    LINKS

    (1) Study finds no evidence of discarded Spartan babies

    Posted Tue 11 Dec 2007, 9:00am AEDT

    http://www.abc.net.au/news/2007-12-11/study-finds-no-evidence-of-discarded-spartan-babies/983848

    (2) Skeletal Remains from Punic Carthage Do Not Support Systematic Sacrifice of Infants

    Jeffrey H. Schwartz, Frank Houghton, Roberto Macchiarelli, Luca Bondioli
    Published: February 17, 2010
    DOI: 10.1371/journal.pone.0009177

    http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0009177

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