Tuesday, 17 December 2013

Are you living in a non-shared environment?


In a previous post, I tried to encourage geneticists to simplify their language. They talk about the genetic code in their own linguistic code, with all the baggage of the past. For example, they say “loci” when the usual word would be “location”. Each dollop of jargon halves the audience.


Now I have a further gripe about geneticists: they are messing up the environment. They refer to it as “shared” or “non-shared”. Every time I come across the phrase “non-shared environmental influences” I have to interpret the negative framing, and slowly deduce the meaning.

I think that what geneticists are talking about are “Personally Created Environments”. For example, I can remember a successful executive telling me that as a young girl she coped with her disruptive family life by creating her own study in a garden shed. It became her refuge, and she felt she blossomed thereafter. To what extent is this an “environmental” effect? Once she had built the shed she had to use it regularly for it to have any influence on her studies. To my mind the important factor was that she wanted to do her homework, and searched out a quiet place to do so. The shed on its own would not have attracted the attention of a less studious child, though with external discipline perhaps the latter might have benefitted from using such a facility.

What is the “shared environment”? I think that is the family, mostly, and the school if all of the family’s children go to the same school. Perhaps it should be called the “Imposed environment” or just “family influences”.

Equally, when listening in the child guidance clinic to Bermondsey mothers talking about their delinquent offspring they often used the phrase “and then he fell into bad company”. Similar in interpretative framework was the lament from young girls “Then I fell pregnant”. I was always tempted to ask the latter “Was any sex involved?”

Perhaps it would be simpler to resuscitate the old concept of “locus of control”. When the locus of control is external, as when a child has family influences imposed on them, or is sent to a school chosen by their parents, then that is the imposed environment. Lead in paint on a window frame is an imposed environmental effect. Governments likewise, until you can vote for them, and even then they will probably be imposed on you against your will half of the time.

When the locus of control is internal then I think we are on more debateable grounds. Perhaps we should call these “Personally created niches”. A garden shed does not blot out all social influences for ever. Even university teachers have to notice the world outside the campus. In my view, personally created niches are aspects of our character which can facilitate us in developing our preferences, but they are not truly environmental effects.

Time to turn to the very best measures of environmental influences, evaluated in detail, and ranked according to the scope for personal agency. References, please.


  1. To quote myself from over at HBD Chick's:

    "The heritability of behavioral traits is typically on order of 50%. However, what’s left (after you subtract the 'shared environment', which is generally 0, but more on that soon) is just the 'unexplained variance.' We don’t know what that is. Much of it, perhaps a good deal, is measurement error. Evidence suggest that that is actually missed heritable influence.

    However, what’s left over, after you’ve accounted for 'attenuated heredity' may be what’s known developmental noise. This is 'environmental' in the sense that it’s not inherited, but is essentially random and not subject to controlled manipulation.

    Or we think it’s random. See Kevin Mitchell on it:


    Even developmental noise appears to [be] heritable, to a degree. Whether or not this is 'on purpose' or an evolutionary accident is unclear.

    And finally, and this is an 'advanced' topic, impact of the 'unique environment' – what makes identical twins raised together different from one another – could itself [be] significantly genetic in nature, because identical twins aren’t actually genetically identical, but have different de novo mutations.

    You see why I’m a little hard on the 'nurturists' out there. Broadly, the evidence has not been kind to 'environmental' influences. Note that this is not to say that they don’t exist."

  2. Niche creation, a personal example: In 7th grade I moved the boxes around in the unheated storage area of our apartment in Alaska to create a small reading space (a niche) away from the noise, commotion, and constant television. I discovered that several of the boxes held a never-used set of the 52 volumes of The Great Books. I began reading at Homer.. (Note however that the volumes ~were~ there, even if never-used.)

    1. So your parents were driven by a sense of duty, or perhaps your early behavior to lay in stocks for your later development. Good. Unless, of course, Homer messed up your life. Long winded, though with a fine turn of phrase.

  3. I agree with JayMan that the non-shared environment may just be noise inherent in the developmental process. Moreover, even if it is genuinely environmental, it's probably not equivalent to a "personally created environment", because self-chosen environments are to a substantial degree under genetic control and thus would not be orthogonal to the genetic variance component.

    I disagree with JayMan about shared environments. The recent Plomin et al. study of educational achievement in the UK showed that the shared environment contributes strongly to exam results (36% or something like that). Countries with more egalitarian and meritocratic school systems than the UK (or the US) may of course have fewer shared environmental influences on test scores.

    1. @Anonymous:

      "I disagree with JayMan about shared environments. The recent Plomin et al. study of educational achievement in the UK showed that the shared environment contributes strongly to exam results (36% or something like that). Countries with more egalitarian and meritocratic school systems than the UK (or the US) may of course have fewer shared environmental influences on test scores."

      That comes under the "more on that soon." Stay tuned!

  4. Let me guess: You would attribute the c2 variance to assortative mating. But that's essentially hand-waving without direct evidence. This study estimated that the effect of parental assortment on adult IQ differences is 11%.

    1. First, let's get it right:

      The shared environment term found in Plomin's study isn't 0.36; that's only for the full sample. If you separate the boys and girls, it's 0.29 for the boys and 0.43 for the girls. Further, we don't need to address the reported value, merely the lower bound of the confidence intervals, which in this case is 0.2 and 0.36, respectively.

      Some of reported shared environment here almost certainly stems from assortative mating. If the impact of that 11% of the variance, that's a significant fraction of the c^2 here.

      The shared environment finding is consistently zero for virtually any trait you can measure. Hence, anything study that reports a non-insignificant shared environment impact indicates that something is seriously wrong somewhere.

      But there's more. As I said, more on that later.

    2. "The shared environment term ...it's 0.29 for the boys and 0.43 for the girls." My, how I laughed.

    3. Because of common observations about the different behaviour patterns seen in the two sexes in childhood and adolescence.

  5. Well-meaning-amateur17 December 2013 at 17:00

    On the subject of simplifying (or clarifying) language, I think "heritability" could stand to be replaced. The man in the street takes it to mean "the extent to which a trait can be inherited." Something like "genetic explanatory power" would seem to be less susceptible of misinterpretation, though I grant that it is more of a mouthful.

  6. Biologists have probably explained till they're blue in the face: culture/environment affects differential reproduction - but individual biological organisms (say, a human) do not evolve - we're a snapshot frozen in time - environment can slightly nudge a snapshot-dude a bit, but it ain't gonna change their biology much (except at the extremes - e.g., starvation, overeating, etc.) the long-term look at it is culture/environment mainly matters in differential reproduction & mainly does NOT matter for an individual biological organism. cheers!

  7. "Countries with more egalitarian and meritocratic school systems than …": if your schools were more meritocratic they'd be less egalitarian.

  8. Matt Ridley covering some of the same topics in a recent blog, "Heritable IQ is a sign of social mobility":


    Good read, but little new there for IQ mavens.

    1. http://menghusblog.wordpress.com/2013/07/31/the-genetics-of-intelligence/ Meng Hu has a more detailed expostion

  9. Any human action is based on your genetics, ie itself. This is for any form of life. A small stone pushed by the wind, falling toward the depression of the valley. An example of environmental influences.
    Even when the individual is analyzed, and no comparative groups, the genetic factor will be crucial in their actions. Genetics is the basis for the structure of an action, therefore all human behavior is directly or indirectly referenced by your genetics. Therefore, there are no environmental factors. They are just an excuse to demagogues or a bio particular way these people interpret the human panacea. All our environmental actions depend on our biological predispositions.
    Some personal stories here about chronoeventual development that resulted in a cognitive or intellectual enrichment. The most important part, you do not just have a whole available material, to develop certain thing, the most important is the perception you have to find some value in some things randomly scattered around the attic of the house. For this intelligence and energy is needed.