14 April 2012

Pedophilia, the brain, and cause-and-effect

One of the questions I commonly receive about MRI research on pedophilia is: How do we know what causes what?  Comparing the brain scans of pedophiles with non-pedophiles gives us a correlation, and correlation does not necessarily mean causation.

It is true that correlation does not equal causation, but that does not mean we are powerless about it either.  To understand how to attack this kind of problem, we need to recall a few important (but pretty rarely discussed) principles of science:

First, no scientific statement will ever be 100% proven.  There is no such thing as a perfect study.  That is, anyone will always be free to reject any result, claiming the lack of perfection of whatever study(ies).

Next is parsimony: Because we cannot prove anything, the best science can do is explicate each of the possibilities and to pick the best answer available. In science, the best means the most parsimonious; that is, the simplest explanation for the data.
Finally, we need to remember that there exist only three possible interpretations of a correlation:

  • X causes Y.
  • Y causes X.
  • Some third variable, W, causes both X and Y. 

Although it is true that we cannot conclude that X causes Y directly from a correlation, we can come to that conclusion indirectly, using a process of elimination to show that the other two possibilities are inferior (less parsimonious) explanations for the correlation. This is best shown by concrete example:

For folks who do not already know about them, my team and I have found that pedophiles differ from teleiophiles (i.e., "adult-ophiles") in terms of their IQ and memory test scores, physical height, handedness, history of school grade failures, history of head injuries before (but not after) age 13, and on MRIs (in large regions of white matter).

In conducting our work, we purposefully focussed on variables that had a very specific property:  We chose characteristics that happened or were set before the sexual offenses occurred.  Although we can calculate only a correlation between handedness (for example) and having committed sexual offenses, we know that handedness is present even before birth.  (Fetuses have a preference for which thumb they suck in utero, for example.)  So, even though we have only a correlation, we know that sex offenses cannot cause handedness.  Thus, of the three causal possibilities, we can already rule one out.  It was this logic that led us to study height (cannot be changed by commiting an offense), experiencing childhood head injuries (can't go back in time), etc.

So, we now have two possibilities: X causes Y, or some still unknown variable causes both X and Y.  The still-unknown variable explanation is still in the cards, but it is a much less parsimonious explanation. That is, although it is certainly remains possible that some third variable causes both the brain differences and pedophilia, there is no known behavior capable causing the white matter differences that we detected.  So, for the "third-variable" explanation to be true, we would have to posit the existance (on the basis of no evidence) of factors unlike any ever reported before.  So, despite that that is possible, it is not the most parsimonious explanation.

So, that's where we are today.  We do not have proof of causality, and we never will.  (It isn't as if we will ever be able to randomly assign subjects to groups.)  Rather, X causes Y is the best explanation we have.

And that's the best a scientist can hope for.


  1. So can one conclude that pedophiles are made? It seems to me (a non-medical person) that structures in the brain can change if stimuli is introduced to the young child. For example if the child was sexually abused this can affect the wiring of the brain. Then it becomes plausible that pedophilia is made and not an inherent sexuality that some claim. The problem I see is that there isn't enough research into what the stimuli could be that creates changes in the brains of pedophiles because it is such a taboo subject. It seems research is done after they have sexually offended as opposed to before this occurs. From what I have read male pedophiles have a tougher time acknowledging they were sexually abused because they tend to believe that as a child they were the seducers. It becomes to hard for them to acknowledge they were victimized because in society it is easier to accept females being victims. It is hard to change a belief that challenges the very essence of a pedophile. If one believes they are born a pedophile then they will be less likely to accept that their pedophilia was made. You do good work. Rosie

  2. Hi, Rosie; thank you for your kind words.

    You are exactly correct that a large proportion of child molesters (about a third) say that they themselves were molested as children. You are also correct that people who suffer abuse in childhood show brain differences from those who did not. However, I believe it is unlikely that the sexual abuse causes the pedophilia. To understand why, we need to add some other pieces to the overall puzzle:

    The first is that the parts of the brain that appear to change after abuse are entirely different from the parts of the brain that appear to make pedophiles different from non-pedophiles. If abuse causes brain changes that in turn cause pedophilia, then the same parts of the brain should be coming out of both kinds of studies.

    The next piece is that the brain differences associated with suffering sexual abuse are also associated with physical (non-sexual) abuse and with neglect. That is, we don’t have evidence of like-begets-like; rather, it seems that the abuse-related brain differences result from prolonged childhood stress in general.

    Finally, is the large sex difference. All (or nearly all) pedophiles are male, whereas the majority of the victims are female. A like-begets-like mechanism can’t easily account for that.

    So, although other explanations of what’s going are certainly possible (and always will be), the simplest explanation is that a single (still unidentified) problem in development causes all of the reported differences (lower IQ, handedness differences, etc.) and that pedophilia is one that catches attention.

    I hope that’s a help.

    - James

  3. James,

    Thank you for your work on this subject. I suffer from pedophilia, and as you differentiated in your article on CNN, I am not a child molester.

    I'm fascinated by the research about brain differences between pedophiles and non-pedophiles. I'm sure I must have less white matter in my brain, and I'd be really interested to find out for sure.

    I'm left handed, but not shorter than average, and I'm not under-averagely intelligent. I was reading books when I was two years old, and I was a very intelligent young kid. But I do feel like for most of my life there's been something wrong with my brain; I get facts confused easily, I can never remember details, and when I know a fact, I have an unusually hard time retrieving it from my memory; things such as words, names, etc. I know this is common, but I think my case is worse than others.

    Anyway, I was wondering, if somebody suffered from they type of white matter loss which may indicate Pedophilia, what type of cognitive problems might they have? Would it vary a lot, or might someone be able to make some sort of written test which a pedophile would be less likely to pass?

    Also, I did some other reading and noticed that other problems such as Multiple Sclerosis are somehow related to white matter deficiencies. Auto-immune diseases (although I'm not sure about MS) run in my family, and I have Crohn's disease. I'm wondering if there could be a connection.

    Anyway, I'm around 40 years old, I've come to terms with this problem I have, and I'm really interested in learning more and possibly helping researchers to learn more about this problem.

    The fact that it's been linked to a physical brain problem is of huge comfort to me. In the past I've blamed myself, and I've been unable to tell anybody about my problem. To know that this is something which was never in my control is very helpful to know. And now I almost feel like if I brought your article with me to show "it's not my fault", maybe I could seek help from doctors or others. Not that I need help to keep from doing anything illegal, but it does take a toll mentally; knowing I'll live the rest of my life alone.

    Anyway, I think the research you are doing is very important, and I really appreciate it. If there is anything I can help with (like being a guinea pig), I'd be happy to.

  4. Sorry, a couple more questions; you mentioned in one of your other answers that pedophilia is rare. Do you have an idea of how rare it is?

    You are not able to positively identify a pedophile from a brain scan, are you? If not, do you know what percentage of people in general suffer from this lack of white matter in their brain?

    I'm just curious if there are possibly a lot more pedophiles around than people think. Some, like me, don't act out, so they are never discovered. And with all of the recent publicity and outrage over child molesters, I would think that a higher percentage of them are like me. Before recent times, a larger percentage of pedophiles probably acted out, but a smaller percentage of those were probably caught. So in either time, there were probably a lot of pedophiles around who were not known to be pedophiles.

  5. Hi, Cantor.

    Maybe you could enlighten me with your point of view. I'm wondering what's "Perversion", so I would like to know, What do you understand by "Perversion" is it just atypical sex or you understand it in another way ?

    Thank you,

    1. “Perversion” is The N Word of sexology.

      It used to be used to refer to >very< atypical sexual interests. The term then took on the stigma that the sexual interests themselves had, so (most) professionals started using other terms. Unfortunately, it’s a continuing cycle. The new terms then started taking on the same stigma, so still more terms came to be used, and so on. Personally, I believe that fighting the stigma of the actual sexualities is much more important than the stigma of whatever term.

  6. pedophiles themselves must have been abused or exposed to sexual matters as in watching porn through internet. it starts of as a mere means of pleasure and eventually it becomes a means of pleasure. children often becomes vulnerable to sexual attachments since they are naive in such matters and once any child experiencing such a stimulation , they will have lower interest in studies and will have more curiosity towards experiencing this strange and fascinating experience and these children will harbor a kind of sexual attachment towards the exploiting person. when they become adults some are seen to develop remorse up to the extend of committing suicide while others carry on with their lives and have a suppressed sexual desire towards children. may be this talk is taboo . but the incidence is on the rise in the area where i live. and before matters get out of hand pornography and content leading to demoralization should be removed or else. the society in the future holds no hope and pedophilia will become a common occurrence.

    almost everyone is born normal. sexual dependence is inherited. earlier activation of a genetic response will lead to pedophilia in any individual unless he or she is given moral counseling. the neural network records every action and the interplay of conscious and subconscious mind will decide what kind of character a person may develop.

    1. That one learns one's sexuality instead of figuring out one's innate sexuality is a very old idea. Despite all the time, however, no one has ever produced any good evidence connecting being abused causing pedophilia.

      There IS, however, good evidence that suffering childhood adversity in general---whether violence, sexual abuse, or neglect---causes criminality and impulsiveness in general. That is, there can be association among the behaviours, but not among the underlying sexual interests.

  7. I wonder if seeing someone buy viagra online at an alarming rate could be an effect of pedophilia.

  8. "Finally, we need to remember that there exist only three possible interpretations of a correlation:

    X causes Y.
    Y causes X.
    Some third variable, W, causes both X and Y. "

    There is the possibility of a type I error. Although that may be less parsimonious than other options unless you compared enough things that you statistically expect a type 1 error based on your confidence interval and sample size.

    1. Yes. In the above, I mean to say that, in the abstract, there are three ways to interpret an >actual< correlations. You are entirely correct, however, that an >observed< correlation can also be a fluke rather than be an actual correlation in the first place.