1 May 2007

The Nurture Assumption

Filed under: Psychology — ktismatics @ 1:03 pm

[This post is based mostly on The Nurture Assumption, 1998 by Judith Harris.]

Nature versus nurture? We know how to answer such questions: a little of both. As a parent I wonder how much impact my crappy parenting is likely to have on my daughter’s development. We assume there’s a big parenting impact, but even our own experiences aren’t so clear-cut. My father isn’t a particularly warm person, and neither am I. Did I learn to be that way from him, or did I inerit his coolness genes? Similarly, my daughter doesn’t much like hugging, and neither do I. Nature or nurture?

Since most of us are raised by our biological parents, it’s hard to parse apart the influences. All is not lost, though, when we live in a society where it’s possible to identify identical twins who were separated in infancy and raised in different homes. The gist is this: as adults, twins raised apart are quite similar to one another on all sorts of personality measures. So what about twins raised together, in the same home, by the same parents — how similar must they be? In fact, says Harris, they are no more alike than identical twins raised apart. Behavioral genetic studies continue to show that the family home has few, if any, lasting effects on the people who grew up in it.

In the sixties psychologists studied the effects of three contrasting parenting styles: authoritarian, permissive, and authoritative — or what Harris calls too hard, too soft, and just right. The “just right” combines the love and approval of the “too soft” with the setting of enforceable limits of the “too hard.” In short, Just Right parents are exactly what end-of-the-twentieth-century middle-class Americans of European descent think that parents ought to be. There is modest empirical support for the conclusion that children of Just Right parents get along better in social situations and do better in school. However, in Asian-American families the Too Hard parenting style works just as well as the Just Right. In Asian cultures, strict parenting is the cultural norm; in America it’s not. American parents who employ the Too Hard method either are out of touch with cultural expectations — i.e., the parents are social misfits or prone to aggression — or else their kids don’t respond well to the Just Right style — i.e., they’re temperamentally resistant to ordinary techniques of socialization. Or both: inappropriately aggressive adults pass their genes on to the next generation, producing inappropriately aggressive children.

In recent posts we discussed findings showing that parents who are attuned to their infants establish a more effective learning environment for their children. The child senses her similarity to her parent, making it easier to take the parent’s perspective in joint attention tasks. Also, consistent emotional attunement provides a more secure base from which the child can explore the environment. In fact, the attentive, supportive, empathic attitudes and behaviors these parents exhibit are precisely the kind that we would expect to see their children exhibit. Maybe these parents children simply inherit their parent’s orientation genetically rather than learning it from them. Again, the twins-reared-apart studies show no measurable lasting effects of parenting techniques.

Children raised in broken homes are more likely to have difficulties in maintaining stable marriage-type relationships. Again Harris looks at studies of twins and siblings.

The analysis churned out by the researchers’ computer was boringly similar to those of other behavioral genetic studies: about half of the variation in the risk of divorce could be attributed to genetic influences — to genes shared with twins or parents. The other half was due to environmental causes. But none of the variation could be blamed on the home the twins grew up in. Any similarities in their marital histories could be fully accounted for by the genes they share. Their shared experiences — experienced at the same age, since they were twins — of parental harmony or conflict, of parental togetherness or apartness, had no detectable effect… Don’t look for a divorce gene. Look instead for traits that increase the risk of almost any kind of unfavorable outcome in life. Traits that make people harder to get along with — aggressiveness, insensitivity to the feelings of others. Traits that increase the chances they will make unwise choices — impulsiveness, a tendency to be easily bored.



  1. I’m not so certain that this is entirely true. In our experience with kids with developmental disorders, we find that parental involvement in the therapy process makes a huge difference to the rate of progress of kids almost independent of how severely affected they are when first starting. Of course these are not ‘normal’ kids and we deal with 2 to 10 yr olds, but nurture is very important at these age groups.


    Comment by ponnvandu — 1 May 2007 @ 8:20 pm

  2. It’s possible that there’s something innately different about parents who can involve themselves effectively versus those who cannot. Perhaps this genetic ability to engage has been passed on to the child, letting the child respond to parental involvement. Whether it’s a parent or someone else, the adult participating with the child in a “referential triangle” of joint attention remains the critical learning context for all kids, including those with learning disorders. Harris’ position is that most adults are “good enough parents” to get the job done. And also, she emphasizes that the cause of learning disability cannot be attributed to parents who are not “good enough” nurturers.


    Comment by ktismatics — 1 May 2007 @ 9:26 pm

  3. Throughout your past several posts I keep thinking about the question of whether or not there is a “core” self. Is there something that comprises the “essence” of “me”? Or am I the product of a myriad of forces and desires and inputs and genetic programing – nature and/or nurture?

    Locke suggested something to the order of a “blank slate.” I wonder how much this Modernist/Enlightenment/Empirical philosopher’s conception of self-hood parallels with our current discussions and also with the postmodern (Lacan in particular) conception of the self. Perhaps there is a certain continuity between Locke and postmodern psychology?


    Comment by Jonathan Erdman — 2 May 2007 @ 2:02 am

  4. On parental response, we see three scenarios, first are the parents who say “do your job, take this kid off my hands” then the laid back ones who don’t seem to change much and finally the fully involved ones who jump in and get going. Sometimes one spouse is one way and the other is another.

    This response could be genetic but the effect of the type of response is consistent. Involved parenting, even if it just one spouse, results in much faster change.

    Certainly with developmentally challenged kids, parental involvement in nurture makes a big difference. Oddly enough, this is even true when the involvement gets adversarial, the parent and the therapist disagree and seem to fight over every little thing!


    Comment by samlcarr — 2 May 2007 @ 7:55 am

  5. I also echo Jon’s excellent question on tabula rasa.


    Comment by samlcarr — 2 May 2007 @ 7:57 am

  6. Jonathan and Sam –

    It is a good question. For Locke there are no innate ideas, and to that extent the research I’ve been summarizing accord’s with Locke. On the other hand, Locke doesn’t presume much active construction of ideas. A blank slate is a passive receiver of impressions coming in from the outside. Impressions from the world inscribe themselves as ideas in the brain. Simple impressions become connected to one another by association, and so simple ideas assemble themselves into complex ideas.

    What seems more accurate is that the brain has an innate capability of manipulating impressions it receives from the world, actively transforming these impressions into thoughts and ideas. The human brain is also innately equipped to receive and transform not just raw impressions from the world, but also thoughts and ideas that other people have created from raw impressions. Language is the primary means of transmitting and receiving ideas. Using language demands joint attention between speaker and listener, as well as joint intentionality toward understanding the world and one another.

    The innate capability to think and to use language does not develop spontaneously and in isolation, like physical growth. Rather, it emerges only through social interaction — which makes sense, since language is itself a means of social interaction.

    This post points to something else that people are equipped with: genetics. Our genes don’t provide us with innate ideas, but they do express themselves in things like competencies, desires, motivations, attitudes. All these genetic predispositions also affect what we pay attention to, how we interact with others, what kinds of ideas we’re capable of thinking up or learning from others, and so on.

    So: No innate ideas. Our brains receive sensory inputs, but these inputs don’t inscribe themselves on the brain as ideas. We use our ideational apparatus actively to transform inputs into other things like simple and complex ideas. Associations between things/ideas are part of the move from simple to complex ideas, as Locke said. But association isn’t just a passive linkage — we construct and experiment with different links. And, importantly, we are able to receive pre-thought ideas via language. We acquire input sensorially, we develop our innate cognitive processing capabilities through interaction with the world and especially with others, what our processing apparatus constructs is determined in part by our genetic predisposions. Hopefully I understand this correctly, and that my explanation is at least partly intelligible.


    Comment by ktismatics — 2 May 2007 @ 10:47 am

  7. What seems more accurate is that the brain has an innate capability of manipulating impressions it receives from the world, actively transforming these impressions into thoughts and ideas. The human brain is also innately equipped to receive and transform not just raw impressions from the world, but also thoughts and ideas that other people have created from raw impressions.

    Now I’m starting to think Kant with his categories of Reason. Rather than the outside world imposing itself upon the mind, the mind imposes structure upon the external world. We do not know the thing in itself, but only our impression of the thing.


    Comment by Jonathan Erdman — 3 May 2007 @ 12:18 pm

  8. On a side note:

    Is it possible that the nature/nurture debate is somewhat relative to the person?

    Some personalities seem to be born with the ability/energy/drive/etc. to shape and mold the world around them to fit into what they think it should be like. They just seem born that way: By nature they are world changers, leaders, champions, the Nietzschean Ubermen.

    Other personalities seem more pliable. They are molded by their environment and seemed to be born to be the followers.

    Perhaps the rest of us fit somewhere in the middle.

    Am I oversimplifying here?


    Comment by Jonathan Erdman — 3 May 2007 @ 1:50 pm

  9. Jonathan –

    Good question about Kant. Let’s assume that we receive impressions of things and that we infer properties of the thing in itself from those impressions. The kinds of impressions we receive are probably not much different from the impressions other animals receive. They, however, probably never worry about the thing in itself. The impressions are good enough to act on: walk on that surface, eat that substance, flee from that creature. It’s this inferential link from impression to substance that’s characteristic of, and probably unique to, human cognition.

    Locke recognized that humans had ideas about things, but he believed that the content of ideas was conveyed in the impressions that inscribed themselves on the mental slate. Kant (whom I haven’t read) pulls impressions apart from ideas. But how do the ideas take shape? He posits a set of idea-categories that are pre-structured in the human mind. But I don’t think that’s right either. The human ability to conceive of ideas matures over time, and like language it requires interaction with the world and other people to develop. Still, only humans are able to develop their ideational capabilities in this way. Here’s Tomasello on the human ability to infer intentionality in other humans:

    Briefly said: nonhuman primates are themselves intentional and causal beings, they just do not understand the world in intentional and causal terms… They do not understand these things, in my view, because they do not understand that the conspecific has intentional and mental states that can potentially be affected… Nonhuman primates see a conspecific moving toward food and may infer, based on past experience, what is likely to happen next, and they may even use intelligent and insightful social strategies to affect what happens next. But human beings see something different. They see a conspecific as trying to obtain food as a goal, and they can attempt to affect this and other intentional and mental states, not just behavior… Nonhuman primates have many cognitive skills involving physical objects and events — including an understanding of relational categories and basic antecedent-consequent event sequences — but they do not perceive or understand underlying causes as mediating the dynamic relations among these objects and events.

    I don’t think it’s necessary to posit that the human brain has an innate idea of intentionality or causality with which we transform sensory input. Intentionality is a plausible description of why beings do what they do; causality is a plausible description of why things follow one another in sequence. But, neither causality nor intentionality can be observed through the senses — they must be inferred. Humans gradually develop the ability to draw such inferences about themselves and other things and beings. It’s an incremental improvement over the basic primate brain, but it makes a lot of difference in the ability to understand phenomena and to learn from one another.


    Comment by ktismatics — 3 May 2007 @ 1:56 pm

  10. Jonathan –

    I think it’s likely that we inherit genetic predispositions toward being leaders or followers. I’d say that both leaders and followers are members of the pack; their identities are established relative to one another in the social system. Presumably the leader is just as driven by her genes as is the follower.

    Leaders might be dominators but they aren’t generally innovators. Even in nonhuman species the discoverers of new food sources are usually the ones who are lower on the group hierarchy, incented to use cleverness rather than strength and numbers to get what they want. This drive and ability of the underling to discover and to create is acknowledged even by Nietzsche, whom I believe had equal disdain for leaders and followers in his own time.


    Comment by ktismatics — 3 May 2007 @ 3:51 pm

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