The Nurture Enigma – How Does the Environment Influence Human Nature?

Ms Smarty-Pants

Historical Background

As some of you are well aware, a predominant idea among intellectuals has been that human nature is shaped by the environment, commonly known as the Tabula Rasa or in English, the Blank Slate. This has been the cornerstone of the Enlightenment, the political and philosophical movement of that grew out of late 1600s England and spread throughout the world (although mainly to countries of Northwest European origin). It was an idea that justified social reforms that greatly improved life for most people who were affected by them.

The Tabula reigned pretty much until 1975 when biologist E. O. Wilson wrote Sociobiology, a book that attempted to use evolution to explain not only animal but also human social behavior. Although this book shook things up in Academia it didn’t make that much impact elsewhere. It wasn’t until the 1980s that the reaction against the Blank Slate began to get serious. At this point in time people in the field of behavioural genetics conducted studies on the heritability of things like personality and intelligence that were so extensive and of such quality that they simply couldn’t be ignored. And they showed substantial heritabilities of not just some traits but all of them, something that still holds today. There were some die hard blank slatists, like biologist Stephen Jay Gould, who persisted but most of the resistance to the idea of an inheritable human nature had waned by the mid 1990s (at least that’s my impression).

So the general idea of all nurture and no nature was losing the battle but the vast majority of people were still unaware of this and continued their lives as if nothing had changed – carefully rearing their children during their “formative years” according to “expert” advice, and feeling great when they turned out good, and feeling guilty when they didn’t.  Then in 1998, a text book writer named Judith Rich Harris wrote a book called The Nurture Assumption, summarizing and popularizing the findings of behavioural geneticists, focusing especially on the implications for child development. This was followed in 2002 by psychologist Steven Pinker’s book The Blank Slate, a broad exposé of the whole nature-nurture issue that in its informative and entertaining style became popular in wider circles. People still talk of the formative years even today (I just got a comment from one of them), but by now the tide has irreversibly shifted.

The Post-Slate Situation

So, what does the “new” research from the 1980s, that is now finally beginning to reach public awareness, tell us about human nature? The most obvious part is that nature is a major factor. This is typically summed up in textbooks in the 50/50 rule, claiming that genes and environment can explain about half of the variance each of things like intelligence, personality, psychopathology etc. Which is easy to remember – but also incorrect. This is due to the fact that there is something called measurement error. Most studies are done in a way that doesn’t distinguish this error from the environmental factor. So it’s 50 percent nature and 50 percent environment plus measurement error. Studies that have managed to minimize measurement error typically yield heritabilities for personality traits and similar characteristics around 70 percent. You also have the fact that some of the traits linked to the most important life outcomes, like intelligence and impulsiveness, have even higher heritabilities, around 0.75-0.80.

Equally important – and especially problematic for the adherents of Enlightenment –  is the distinction between shared environment and non-shared environment. It’s the shared environment – family, school, neighbourhood etc – that would lend itself to social reforms. But the research has consistently shown that this factor is very small, often close to zero. As behavioural geneticist Robert Plomin says,

‘Nurture’ in the nature–nurture debate was implicitly taken to mean shared environment because from Freud onwards, theories of socialization had assumed that children’s environments are doled out on a family-by-family basis.

So while there is still a fair amount of environmental influence, it’s not coming from parents, schools, teachers etc. Some people will never accept this; they are too stuck in their political views, they like to blame their parents for how they turned out or take credit for the success of their children. But rational and intellectually honest people will be forced to accept it.

Judith Rich Harris and the Enigma of Non-Shared Environment

But this still leaves us with a substantial environmental influence of the non-shared variety, the unique experiences of the individual, that undeniably affects our personality and intelligence. So what experiences are we talking about?

Oddly enough, 30 years after behavioural geneticists uncovered the importance of non-shared environment, we still don’t know anything about the nature of this influence. This great mystery that goes right to the heart of human nature seems to be uninteresting to both psychologists and the media. Possibly because of the political implications but it might be that they simply lack ideas or intellectual curiosity. After all, personality psychologists – 95 percent of whom identify as liberal – do not praise the Big Five model for all the theories it has generated but for all the consensus it has achieved. Yay…

But one woman, the above mentioned Judith Rich Harris, is actively searching for answers. In a chapter in the anthology The Evolution of Personality and Individual Differences by psychologists David Buss and Patricia Hawley, she reviews the evidence, the old theories and proposes a new one that could explain the nature of the non-shared environmental influence.

Gene-Environment Interactions

This is not to say that she is the first to have attempted this. Some have claimed that parents, school and all that may still be important because of gene-environment interactions: the fact that the same environmental factor will affect two persons differently because of their different DNA. This would mean that the environment believed to be shared is really unique and non-shared and possibly very important.

While gene-environment interactions do occur, Harris argues that it’s highly unlikely for these interactions to cancel each other out. Would an overbearing teacher make one child anxious but the other calm and confident? Even if some children would become angry by such a teacher this would not be the opposite of anxious but rather two expressions of neuroticism. Apart from being implausible, Harris also points to the fact that interactions seem to be rare and most of the documented cases involve sensitivities in which people have the same reactions in varying degrees, not opposite reactions that would cancel each other out.

Even more damning to this theory is the research on identical twins. If things like family was in fact unique and non-shared due to gene-environment interaction for siblings it could not be that for the twins since they have identical DNAs so no interactions are possible. This would mean that parents, school etc would have a profound effect on all people with the exception of identical twins for whom it would mean little or nothing, which would make them fundamentally different from the rest of us. At the same time identical twins have the same size of shared and non-shared environment influence as everyone else. So even though it would be made up of completely different experiences it would still by some happy accident add up to exactly the same size. It just doesn’t make much sense.

Family Interactions

Another couple of theories that both try to save the idea of family as an important influence on human nature, are those of differential parental treatment and birth order effects. While it has been found that parents do treat their children differentially, Harris mentions research on this that showed no effect of this on the children. Instead it suggested that parents do this as a response to the children’s varying behavior. Which sounds very plausible: you would not expect a parent to lose his or her temper as often with a quiet and conscientious child as with an impulsive and emotionally unstable one.

Research has also failed to provide support for any effects from sibling interactions, a very popular theory. Sibling rivalry is something most people can recall from their childhood. It may seem only natural that all that bickering would have some impact. But to date, there is no evidence of that. Identical twins again provide further evidence to the contrary, since they have been found to compete less with each other (as they should according to the laws of evolution). This would mean that the sibling interaction effect would be smaller on them and we again end up with the idea that identical twins have a different shared environment than the rest of us but that it serendipitously adds up to the exact same size.

The Three Systems Theory

Instead of these half-hearted attempts at rescuing any possible remains of the Blank Slate, Harris proposes a different theory based on evolutionary psychology and especially on the observation that traits or mechanisms tend to evolve to solve specific problems and that they for this reason often are largely independent of each other.  So, what problems and what mechanisms?

Well, we know that personality is more malleable in childhood than in adulthood. This is most likely because the brain’s plasticity gradually decreases over the life span. So the environment should exert most of its influence during childhood. This means that we should look for basic adaptive problems that children face. Harris identifies three such problems: how to form personal relationships, how to fit in among your peers, and how to compete among your peers. To solve these problems she hypothesizes that the brain has evolved three mechanisms or systems which she calls the Relationship System (RS), the Socialization System (SS), and the Status System (STS).

The RS is basically an ever-growing database of information on people along with judgments of them based on that data. Since these judgments are used to relate to people they tend to be emotional – who we love, hate, fear, pity and so on. Another characteristic is that the data collected is consciously retrievable. The RS is the base of gossip; we talk about people we have stored information on and compare notes. Although in the modern world this is often done about celebrities that aren’t socially relevant to us.

The SS also collects data but on social categories – male, female, adult, child, rich, poor etc. This is essential information if you want to fit in because you need to know where to fit in – which social categories apply to you. Unlike the RS that looks at personal experiences of specific individuals, the SS generalizes about groups, stereotypes you might say. It’s the basis of our ingroup/outgroup distinctions, according to Harris. But when did we learn about these categories? At no particular time, it just builds up gradually. So unlike the information in the RS, there is no consciously retrievable memory of it.

Finally, we have the STS which collects information about where we stand in comparison to other people in our social category – because that’s where the competition takes place. The reason for keeping track of all the possible status hierarchies – being funny, smart, tough etc – is that it enables the child to find an optimal competitive strategy. So this system looks for things like respect, appreciation and recognition.

So which of these systems is the most likely mechanism by which non-shared environment can influence personality? Although Harris doesn’t say much about why the RS couldn’t do this, we already know that some central relationships in a child’s life are those with family members – which is shared environment and thus of little importance. Still, close friends seems like a possible candidate here… She points out that the least likely mechanism would be the SS, since this is a process by which the social environment (peers) reduce variance in personality as it makes children conform to the people in their social categories. But the STS looks very promising. When a child looks for an optimal strategy for competition, it isn’t looking to conform but to stand out. And if one niche is taken it will have to look for other venues. Like if you’re a big boy who is moderately funny in a peer group of plenty of really big guys but no one who can tell a joke, you may go against your genetic disposition and become the comedian rather than to assert yourself physically.

Evidence

Now that sounds like a plausible theory, but is there any evidence?

Harris agrees that her theory needs to be tested but she does have some evidence too. She mentions the fact that men who were tall as boys grow up to be more assertive and confident as adults. That height in adolescence predicts salary better than height in adulthood. Although she admits that the same thing that makes a person grow fast (androgens) may also be causing their assertiveness. To get around this Harris suggests that we look at relative age within peer groups. One important peer group is that of classmates in school, in which children can differ in age up to a year. This makes for differences in size and maturity that are unrelated to hormones or other biological factors. This relative age effect can be seen in sports where the older boys in groups of selection are picked up by better teams. This may seem stupid if all you do is select players who happen to be older than their peers. But what if being bigger also give them confidence that in turn make them better players?

A study by Dr Chris J Gee at the University of Toronto, published in the International Journal of Coaching Science gives some support for this idea. Gee has followed promising young hockey players over 15 years in order to see if personality can predict success in the sport. According to the study a composite measure of the typical traits thought to be linked to success – self-confidence, need for achievement, competitiveness etc – did in fact predict success. And in regard to the relative age effect common in drafting, Gee writes,

Interestingly, when height and weight (both commonly cited anthropometric indices used when scouting amateur hockey players) were entered into each of the previously mentioned regression models, they failed to significantly increase the amount of variance accounted for.

This strongly suggests that coaches pick the boys who are oldest in their age group, not because they are bigger or have more androgens or something like that, but because they have certain personality traits associated with athletic success. How did they get those traits if all that distinguishes them from other boys is that they happened to be born earlier? It seems to me that Harris’ theory fit these data very well: these boys became confident and assertive through their social environment of peers who couldn’t push them around. This put them on the track to athletic careers, while others who might have been of average size for their age but the youngest in their age group turned to comedy or some other way of becoming popular and getting status.

I think Harris may be on to something.