Good morning.
The California
travelogue was frivolity and fun. This
piece turns back to research on a question that has long intrigued me and about
which I've commented and speculated. I'd
never taken a dive into the research, however, but I finally did (a shallow
dive, to be sure). If you are uninterested
in the extent to which personality traits are inherited, you can skip this
entirely. It's a one-topic exposition.
There were
two pieces of research published recently that contradicted a belief I've held
for years (ever since I was a graduate student in Psychology in the
mid-1970s). One was publicized in an
article in Quartz titled "You’re
a completely different person at 14 and 77, the longest-running personality
study ever has found." The other
was "Codevelopment of Preschoolers’ Temperament Traits and Social Play
Networks Over an Entire School Year."
In my view,
based on what I learned as a grad student, personality traits are significantly
genetic. Not exclusively, but significantly. One reason I think that is the simple matter
of how we inherit genetically from our parents.
Our eye color, ear shape, head shape, height, and much more are driven
by genetics. Surely the neurons in our
brains grow as they do because of our genes.
Clearly, our brain functions can be affected by the environment (if when
young we're deprived of food or affection, or suffer concussions or illness,
etc., the adult will be different from the genetically-identical
child-turned-adult who doesn't suffer from those effects). It has, however, always seemed to me highly
likely that fundamental personality traits are shaped genetically as well as
environmentally.
To take the
second study first: I wouldn't change
what I think on the basis of this one study.
It appeared in one of the most distinguished psychology journals, the Journal of Personality and Social Psychology,
and reported on research on two pre-school classes for a year. The authors analyzed "personality traits
and social networks for one class of three-year-olds and one class of
four-year-olds." What they found
was that "children whose play partners were extroverted or hard-working
became similar to these peers over time. Children whose play partners were
overanxious and easily frustrated, however, did not take on these particular
traits." In other words, kids have
an effect on kids, and personality "traits" may be learned—shaped by
the environment, not just genes. One of
the investigators, from Michigan State, agreed that "Our finding, that personality
traits are ‘contagious’ among children, flies in the face of common assumptions
that personality is ingrained and can’t be changed. . . . This is important because some personality
traits can help children succeed in life, while others can hold them
back."
I don't
have any reservations about the study itself; the journal abstract suggests
they did a decent job on methodology.
What I am cautious about is generalizing it. One major question is whether the traits and
networks will be long-lasting or ephemeral; do the 3-year-olds and 4-year-olds
retain the new behaviors over time, into adulthood? From this study there's no way to know. I'd also want to see the results replicated
with different age groups using different instruments.
The second
study was based on a survey first administered in 1950 to 1,208 Scots who were
14 years old at the time. Using a
variety of questionnaires to rate them on personality traits, the results were
consolidated into a combined rating for one trait, "dependability." Over 60 years later, researchers found 635 of
the original participants, of whom 174 agreed to do the testing again (now at
age 77). The individuals rated themselves
and had a friend or relative do the same.
There was
little overlap with the results from 63 years earlier. "Correlations suggested no significant
stability of any of the 6 characteristics or their underlying factor,
dependability, over the 63-year interval. . . . We hypothesized that we would find evidence
of personality stability over an even longer period of 63 years, but our
correlations did not support this hypothesis." This was not the result they expected because
most personality studies (that don't cover this length of time) showed more
consistency in the survival of traits over years. "The findings were a surprise to
researchers because previous personality studies, over shorter periods of time,
seemed to show consistency. Studies over several decades, focusing on
participants from childhood to middle age, or from middle age to older age,
showed stable personality traits. But the most recent study, covering the
longest period, suggests that personality stability is disrupted over
time."
The Quartz author made a couple of
thoughtful points. "It’s disconcerting
to think that your entire personality is transformed" over the course of a
long life. The study authors, quoting
earlier work, note that "Personality refers to an individual’s
characteristic patterns of thought, emotion, and behavior, together with the
psychological mechanisms—hidden or not—behind those patterns." If that's true—and the definition seems
reasonable—if there are such dramatic changes over a lifespan, "can you
truly be considered the same person in old age as you were as a teenager?"
One of the
small ways that this can play out is at high school reunions, which were on my
mind because I'd been looking for "missing" classmates. "Perhaps this [big change in people]
won’t surprise you if you’ve had the experience of running into a very old
friend from school, and found a completely different person from the child you
remembered. This research suggests that, as the decades go by, your own younger
self could be similarly unrecognizable."
After
reading the Quartz article, I went to
the original study. The authors hedged
their conclusion more than the article.
They wrote that if they applied a more complex analytical model to their
data, they found a "significant 63-year stability of 1 personality
characteristic, Stability of Moods, and near-significant stability of another,
Conscientiousness." So while it may
be true that people change markedly, it also appears to be the case that
"some aspects of personality in older age may relate to personality in
childhood." It's interesting for me
that "stability of mood" is the characteristic they found that lasts;
I've long thought of myself (as have others) as having a nearly immoveable
temperament. I'm very sad or jubilant
only for short periods; the vast majority of the time I'm neither up nor down,
just perfectly fine (emotionally). That
stability suggests to me it's inherited; that's certainly the way my father
was.
As with any
study like this, there are qualifiers that one must consider. For example, one, is there anything about Scots
or Scottish society that might be different from, say, people from Japan or
India or Brazil? Two, to what extent
might the time period have an effect?
Would one see the same results if one had studied people over six
decades from 1900 – 1960? Three, was
there anything in the initial selection of people that might bias the results
(even given that they were all Scottish, was it a particular segment of
Scottish society?), and, probably more pertinent, is there something about the
174 who survived and were found who were re-surveyed, out of the original 1208,
that could skew the results? There would
have to be a lot of replication of this study to determine how sturdy the
results are—but there just aren't that many groups of people who've been
surveyed over decades in different places around the world.
The
questions these two articles raised sent me to the literature on the
heritability of personality traits. One
article, with four authors from the University of Minnesota, summarized the
state of the research (2008, and not a lot has changed since then, as far as I
can tell).
Individual differences are
heritable, by which we mean that genetic influences make a substantial
contribution to individual differences in peoples’ observable characteristics.
. . . Indeed, this finding is so
universal that Turkheimer enshrined it as the "first law" of behavior
genetics. Turkheimer went on to propose second and third laws as well. The
"second law" states that being raised in the same family has a
smaller effect on individual differences than genetic effects. The "third
law" is that a nontrivial portion of individual differences can be
attributed to effects unique to each individual person, beyond genetic
differences, and also beyond being raised in the same family. These laws are well-supported by an extensive
literature, and they clearly apply to personality as much as they apply to
other individual differences.
They go on to point out that in their view, "the three
behavior genetic laws strike us as vague, albeit of fundamental historical
importance. The 'laws' provided a needed corrective to the idea that people are
puppets with strings pulled by the external environment. Nevertheless, the laws are derived from an
approach to behavior genetic inquiry that estimates genetic and environmental
effects on people in general." The
laws aren't wrong, they are just very general.
("The concept of an overall heritability for a specific
individual-differences variable is meaningful only in a very general
sense. It is akin to estimating, e.g.,
the average yearly temperature for a wide region, such as North America. The
average yearly temperature in North America is not meaningless, it is simply
very general.)
It just happens that in the
last two years there was a major meta-analysis of the research on heritability
of traits based on twin studies (which are, in many ways, the most reliable
studies of human beings). I may have
learned this in graduate school 40+ years ago but I forgot: there is a "big five" in
personality traits, according to one set of authors. It is
one of the most established
and recognized approaches to describe and measure individual differences in
personality, and includes openness to
experience, conscientiousness, extraversion, agreeableness and neuroticism. Although openness captures imagination and
intellectual curiosity, conscientiousness refers to carefulness and
organizational ability. Extraversion is defined by positive emotions, such as
gregariousness and the tendency to seek out stimulation. Neuroticism includes negative emotions, such
as anxiety and depression, and is commonly defined as emotional instability,
and agreeableness describes an individual’s level of cooperativeness and
compassion. (My emphasis, just to highlight
the five.)
These researchers pointed to one study, using about 275
pairs of twins (fraternal and identical, or dizygotic and monozygotic), that
concluded that "broad genetic influence on the five dimensions of
Neuroticism, Extraversion, Openness, Agreeableness, and Conscientiousness was
estimated at 41%, 53%, 61%, 41%, and 44%, respectively."
One needs to be clear, as the
Minnesota authors caution, that "when researchers conclude that 'the
heritability of extraversion is 50%,' they are concluding that 50% of the total
variance in extraversion in their sample is associated with genetic influences.
They cannot conclude that a specific person's extraversion level is '50%
genetic;' the concept of heritability applies not to individuals, but rather,
to differences among many individuals."
(For example, there may be sex differences in the heritability of
"agreeableness," so looking separately at men and women might lead to
different conclusions than looking at the variance for the entire population.)
Given the
methodology and definitional questions, the authors of the meta-analysis looked
at "virtually all twin studies published in the past 50 years, on a wide
range of traits and reporting on more than 14 million twin pairs across 39
different countries." They
concluded: "Our results provide compelling
evidence that all human traits are heritable:
not one trait had a weighted heritability estimate of zero. The relative
influences of genes and environment are not randomly distributed across all
traits but cluster in functional domains."
They didn't attach percentages by trait but concluded that "across
all traits the reported heritability is 49%." (Again, may vary by sex, geographic location,
and so on.)
If those percentages are
correct, that's a big part of our personality that comes from our genes.
A long-time colleague of
mine, and one of his colleagues, provided a concise summary of the state of the
research in the field of behavior genetics, of which the study of personality
is a part:
There is abundant evidence .
. . that personality traits are substantially influenced by the genes. Much remains to be understood about how and
why this is the case. . . . In the long
run, but not yet, approaches via molecular genetics and brain physiology may
also make decisive contributions to understanding the heritability of
personality traits.
What does
this all mean for parents? "For
most adolescents, in families with normative levels of conflict, personality
does result from genetic factors and environments that make people different
from their family members." So
family dynamics, if within the range of "normal," won't differentiate
children from each other. It also
suggests that part of the personality of one's children is driven by their genetic
inheritance—how much, and which parts, likely vary by individual, sex, and
other non-personality differences—and part is by the environment they are
raised in, both inside and outside the home.
So both biological and adoptive parents know they can have an effect
after birth.
What no one knows with
certainty is how much malleability there is.
What we do know is that a child is not a tabula rasa, in the phrase made
well known by John Locke in his 1689 Essay
Concerning Human Understanding. (The
concept has been addressed by Aristotle, Thomas Aquinas, and Avicenna, among
others, and is in essence "the theory that at birth the (human) mind is a
'blank slate' without rules for processing data, and that data is [sic] added
and rules for processing are formed solely by
one's sensory experiences. . . .
tabula rasa meant that the mind of the individual was born
blank, and it also emphasized the freedom of individuals to author their
own soul." We just don't know
how much has already been written on the slate.
I'll return
to more light-hearted topics in the near future!
Today, more
snow for us, then back into the deep freeze over the weekend. Oh joy.
Gary
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