Nature = 50, nurture = 0

Posted:
in General Discussion edited January 2014
There's a great deal of behavioral genetics research now, and it shows that our personalities, attitudes, and other traits are about 50% genetically determined overall. But of the other 50%, virtually none of it is predictable. Nature = 50, nurture = 0.



A book I just read called The Blank Slate by Steven Pinker really makes this case. He argues that we have an assumption that we're all a blank slate, that your experiences determine who you are, and it's very inconsistent with most of the new (well, in the last quarter century) research.



Especially during the 1960s, there was an assumption that everyone is born equal, and that if you just treat people a certain way, you can change everything. It's a very egalitarian approach. But, along with Margaret Mead's work, it seems to be mostly bunk.



Another ridiculous example of this belief in the blank slate is shown in the book "As nature made him." On advice from a psychologist, a Canadian couple in the 1960s decided to make their son into a girl after a circumcision accident. The psychologist's theory was that all gender differences were due to socialization, so you could take a boy and dress him up as a girl and give him dolls, and with the right plastic surgery, you'd have a girl. The book is about how wrong they were.



Here's a recent quick summary of behavioral genetics from some leaders in the field:

Quote:

There are two striking findings. The first is that nearly all behaviors that have been studied show moderate to high heritability--usually, to a somewhat greater degree than do many common physical diseases. Second, although environment plays a role, its contribution tends to be of the nonshared type, that is, environmental factors make people different from, rather than similar to, their relatives.





Quote:

How much heritability? Estimates of genetic and environmental effects from recent twin studies. A, additive genetic variance, or heritability; C, variance explained by shared environment; E, variance resulting from nonshared environment and errors of measurement.



That stuff about nonshared variance (the dark pink bars) being small is really important. The idea is that identical twins raised together are no more similar than identical twins raised apart. What that means is that nurture has virtually no predictable influence.



Nature's contribution = 50%, nurture = 0%, maybe 5%. What about the other 45-50%? It just not predictable. It's error variance, in statistical terms.



And notice in that graph that the IQ of the child shows some effect of shared environment, but not the IQ of the adult. That means that any effect of nurture you do experience as a child "wears off" by the time you become an adult.



This has led some authors to conclude that parenting doesn't matter. Judith Harris published an article and a book that makes this argument:

Quote:

children would develop into the same sort of adults if we left them in their homes, their schools, their neighborhoods, and their cultural or subcultural groups, but switched all the parents around.



Lots of people think that parents should be punished for their children's bad behavior, or if you see a child acting up in the grocery store, they automatically assume that it's the bad parent's fault. This type of research suggests that parents don't influence the temperament of their children very much, if at all.



I find this fascinating. All of our assumptions about human nature are basically wrong. It's really turning behavioral and social sciences upside down, and I don't think the general public has quite caught up with it yet.



Comments? Do you buy it?
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Comments

  • Reply 1 of 50
    bungebunge Posts: 7,329member
    I'm definitely too drunk to take all of this in right now, but from what you're saying I do find it fascinating. Enough so that I'll re-read this tomorrow.



    Nurture - 0? Wow.
  • Reply 2 of 50
    _ alliance __ alliance _ Posts: 2,070member
    well i didn't read most of yer post.

    but i will tell you the research community in the genetics department of current professors throughout the field agree that how we are raised determines the type of person we become a great deal more than our genetics. i have heard quotes up in the 90% range, but i dont know how accurate that is. studying this type of science in great detail, i will add that i believe this is correct. there is no way that i could ever buy, knowing what i know now, that genetics plays that huge of a role in who we really are. it determines our molecular traits, which leads to our physical traits, but our personality is primarily linked to the field of psychology and not genetics. i hope i am being clear here--i just had brain surgery and my thoughts aren't quite what they used to be...
  • Reply 3 of 50
    alcimedesalcimedes Posts: 5,486member
    i have a close friend who worked at the U of MN twins study. (lots of studies, tons of research).



    he couldn't give out any details of course, but they ran into this a lot. a scary amount of very strange things seem dependent on genetics. however, their studies showed a fair amount was affected by nurture. i would want to see a lot more studies coming out to support this before taking it at face value.



    other than reading through the entire methods section of their study, i couldn't say if there were any problems in their study. i always find this kind of stuff fascinating though.
  • Reply 4 of 50
    chinneychinney Posts: 1,019member
    I think that all of the studies must assume that the subjects involved had reasonably loving and involved parents. Children who do not get love and reassurance - especially in their earliest years - never develop into functional adults. Children who are abused, at any age, disproportionately develop severe social problems.



    I don't much like Pinker's overall worldview and I don't believe in the blank slate argument. But don't kid yourself, parenting matters - a least in terms of providing a base level of care and support required for children to grow.
  • Reply 5 of 50
    brussellbrussell Posts: 9,812member
    Quote:

    Originally posted by alcimedes

    i have a close friend who worked at the U of MN twins study. (lots of studies, tons of research).



    he couldn't give out any details of course, but they ran into this a lot. a scary amount of very strange things seem dependent on genetics. however, their studies showed a fair amount was affected by nurture. i would want to see a lot more studies coming out to support this before taking it at face value.



    other than reading through the entire methods section of their study, i couldn't say if there were any problems in their study. i always find this kind of stuff fascinating though.




    Yeah, it's the US's largest center for twin studies. Lykken directs it, or used to. This just occurred to me, but it doesn't have anything to do with the "Minnesota Twins" sports team, does it?
  • Reply 6 of 50
    alcimedesalcimedes Posts: 5,486member
    nah, MN Twins is based on the Twin Cities. (Minneapolis and St. Paul)



    they're basically touching but on opposite sides of the Mississippi river.



  • Reply 7 of 50
    brussellbrussell Posts: 9,812member
    Quote:

    Originally posted by Chinney

    I think that all of the studies must assume that the subjects involved had reasonably loving and involved parents. Children who do not get love and reassurance - especially in their earliest years - never develop into functional adults. Children who are abused, at any age, disproportionately develop severe social problems.



    It seems hard to believe that severe neglect would have no effect. Genie, for example. But then why doesn't it show up in the studies? Perhaps those kinds of extremes are so rare, that basically you can take 99.9% of parents and not see a difference. Maybe the studies just haven't used many (if any) severely abusive parents.



    As I understand Harris's argument, it's that your culture raises your child more than you do. The TV, their friends, their schoolmates and teachers, etc. Parents have a very hard time busting through all those factors to make an impact. Perhaps a very extreme parenting style would make a difference, but not the vast majority of parents in our culture.
  • Reply 8 of 50
    brussellbrussell Posts: 9,812member
    Quote:

    Originally posted by alcimedes

    nah, MN Twins is based on the Twin Cities. (Minneapolis and St. Paul)



    Oh yeah.
  • Reply 9 of 50
    brussellbrussell Posts: 9,812member
    Quote:

    Originally posted by _ alliance _

    well i didn't read most of yer post.

    but i will tell you the research community in the genetics department of current professors throughout the field agree that how we are raised determines the type of person we become a great deal more than our genetics.




    The authors I cited would say that people, and maybe even the researchers, are basically in denial about the situation. The data speak for themselves. (That sounds weird.)



    The books "The Blank Slate" and "The Nurture Assumption" talk about how much resistance there is to this idea. It's just part of our ingrained belief system. We want to believe that we're all "equal" and that anyone can do anything or be anyone we want.



    I did go on too long in my first post. The basic idea is that 1) they've figured out that genes play a much larger role than we've always thought and 2) they haven't figured out what about the environment does play a role. Sure, if we accept that 50% of our traits are determined by genes, that leaves 50% left over. The problem is that no one has been able to pin down any more than a couple percent of that left over. And lots of research shows that nurture doesn't have any effect - twins raised together are no more similar than twins raised apart.



    [edit: brain surgery??]
  • Reply 10 of 50
    Genes can be altered by environment.
  • Reply 11 of 50
    mrmistermrmister Posts: 1,095member
    is there anyone who posts here who works in these fields and knows anything about these matters? that would be refreshing.
  • Reply 12 of 50
    trumptmantrumptman Posts: 16,452member
    I had read some studies similar to this. However what I would like to know is if these studies considered the nurturing environment to extend beyond the parents.



    I have read in many ways parents are actually a very small influence on their children (and this influence is greatest in the formative early years) but that the community at large and peer groups have much more influence.



    So I suppose what I asking is that did they norm for say the twins peer groups in addition to their parents. I read the article linked and it made the assertion that peer groups provide a profound influence, much more so than the parents. However it mentioned that some parents and also groups of parents, perhaps acting as an extended family, or connected culturally, religiously, etc could also exhibit the effect of acting as a peer group and bring about influence.



    The long term trend of these studies sociologically could be very interesting. If we discover that parents as a group need society at large to help bring about the proper influence of nurturing into the equation (so it doesn't = 0) then it will give is all an excuse to stick our nose in each others business.



    Oh there was one interesting section of the article that addressed the background assumptions of researchers regarding the twin studies. For example if both twins went to schools in different towns, the genetic researchers would classify this as different where as socially if they were both k-12 public schools, most of us would classify this as a similarity. Just a little point of interest about the researcher bias there. It was also sort of neat to see the questioning outside out own cultural context. The examples where parenting styles were allowed to be much more authoritiarian than what we tolerate here and also where individual behavior is judged and even punished in a group context would make for interesting questions and research as well. Perhaps it isn't that nurture doesn't have an influence, just the U.S. version of nuture with an extreme reliance on individual freedoms. (snicker)



    See before I could insure that my children only watched what I wanted on my television. However now I have to insure the whole peer group that influences my child doesn't watch certain shows and thus must insure the local movie theater doesn't show certain movies either.



    It could lead to some interesting conclusions from various members of society.



    Nick
  • Reply 13 of 50
    pfflampfflam Posts: 5,053member
    Its the kind of reductionism that would seem appropriate from someone who takes his AI name from Bertrand Russell





    So, if the genes are completely responcible for one's greatness then those of us who are descendants of royalty should have a natural advantage since we have always had that natural advantage . . . right?!?!?



    [in stodgy upper-crust Brit accent] yyyaaaarr, old boy, we knew that all along . . . good breeeeeedingg good blooooooood . .yyaawr[/accent]



    No but seriously, there is a give and take between environment and biology. The geneticists see what they behold and everything that they care about is genes and the reduction of experience to a science through which they can make a name for themselves, or, get tenure, or get another research grant etc



    I doubt I would ever live to see a genetic scientist come to a conclusion that acknowledges Freudian metapsychology, much less see them actually expand their insights beyond their horizons and understand the notions of repression

    or even notions of interpretaion that put into question the assumed sovereign authority of the scientist ensconced in his "OBJECTIVITY"

    . . even when they acknowledge that it is a perspective conditioned by the genetics: meaning, that they (the scientist) are perspectives genetically conditioned to make them see the world as genetically conditioned . . .no?!?!?



    anyway, science will try as hard is it can it will still not take the mystery and awesomeness out of Being . . . unless you mistake its descriptions for truth
  • Reply 14 of 50
    Quote:

    Originally posted by Existence

    Genes can be altered by environment.





  • Reply 15 of 50
    alcimedesalcimedes Posts: 5,486member
    for example Agent Orange actually mutated people's DNA, which screwe up their kids.
  • Reply 16 of 50
    chinneychinney Posts: 1,019member
    Quote:

    Originally posted by mrmister

    is there anyone who posts here who works in these fields and knows anything about these matters? that would be refreshing.



    I suppose you could say that about most posts in most threads.



    But if you would think that the comments of persons other than experts are not worthwhile (and I am not saying that you are asserting this), I would disagree.



    I think that we are all interested in the official line from the experts. However, comments and opinions of persons other than experts are interesting and worthwhile as well. Informed general debate is the very thing that should, in my view, be stimulated.
  • Reply 17 of 50
    giantgiant Posts: 6,041member
    Quote:

    Originally posted by BRussell

    Comments? Do you buy it?



    I highly suggest that anyone interested in the validity of genetic determinism read Gould's Mismeasure of Man. I don't think anyone can have a valid understanding of these kinds of studies until both their history and the interpreted nature of science is understood.



    I didn't read the report that gous along with the posted chart, but any study that uses IQ to prove a point, specifically about heredity, resides in a bubble of ignorance. I think more than enough people have thoroughly debunked not only IQ testing but the repeated historical attempts to link it to heredity.



    Another good book is Kitcher's Science, Truth and Democracy, though Gould's specifically discusses attempts to link IQ with heredity.
  • Reply 18 of 50
    thttht Posts: 3,046member
    Quote:

    Originally posted by BRussell

    Comments? Do you buy it?



    This has been my observation for awhile. I probably disagree on some of the details, but overall, I buy it. I think one can start seeing personality traits in kids as young as 2 years old. One thing that is confusing in this discussion is that inheritable personality traits (volitality, passivity, et al) can be overridden or overshadowed, masked, by learned behavior, so, it's hard to determine what was inherited and what was learned.



    But yes, I can buy into 50%.
  • Reply 19 of 50
    I dont buy it. The parents teach the child what is right and wrong. They teach them alot not knowing, children like to copy things other people do because they think it must be right. the right/wrong thinkg greatly determines a persons personality in my opinion. it should be more like 25%.
  • Reply 20 of 50
    I don´t buy anything that tries to put % on what is what.
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