This 2011 study published in The Journal of Developmental Psychopathology

investigates children’s prosocial behavior and its relationship to parenting style and child genetic

profile. Specifically, the team looked at gene polymorphisms of the D4 dopamine receptor and

its influence on the prosocial behavior of children. The study joins the growing body of literature

showing that “genetic factors contribute to children and adolescents’ prosocial behavior” (Knafo

et al., 2011, p. 57). Additionally, it contributes to a larger conversation exploring how similar

environmental influences yield varying effects on children’s behavior. This phenomenon has

been called, among other terms “differential susceptibility” (Knafo et al., 2011, p. 57 as cited in

Belsky & Pluess, 2009). The concept of differential susceptibility expands on the prevailing

diathesis-stress model. The diathesis-stress model underscores how some people possess certain

gene variants increasing their likelihood of developing a particular pathology when a certain

environmental conditions occur in their life. Differential susceptibility, on the other hand, moves

away from genetic “vulnerability” mediated by environment, and frames the picture as an overall

genetic sensitivity to environment—both “positive” and “negative” (Belsky & Pluess, 2009, p.

904). This collaborative effort by researchers from Hebrew University of Jerusalem, Duke

University, and The National University of Singapore stands at the intersection of knowledge

based in developmental psychology, molecular genetics, neurobiology, and even

neuroeconomics—an interdisciplinary science investigating human decision making and how

brain functioning informs decision making (http://dibs.duke.edu/research/d-cides).

Methodology

Researchers for this quantitative twin design study wanted to find out more about the

variation in prosocial behavior in children aged approximately 3.5 years (mean age= 43.81

months). Participant families were part of the Longitudinal Israeli Study of Twins, “whose focus

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is on children’s social development as influenced by genetics, abilities and socialization” (Knafo

et al., 2011, p. 57). Of the 168 children included, 19 were a monozygotic (identical) twin pair,

53 were a dizygotic (fraternal) twin pair, and 27 were a singleton sibling pair. Twin zygosity was

measured using parent questionnaire as well as DNA testing. Assessments about each child’s

general cognitive abilities were made, as well as assessments about their prosocial behavior in

the six different laboratory-setting situations.

Assessing prosocial behavior quantitatively

For the purpose of the study, researchers Knafo, Israel, and Ebstein define prosocial

behavior as “voluntary behavior enacted with the intent of benefiting others” (Knafo et al., 2011,

58). The reserachers made a distinction between “self-initiated” versus “compliant” prosocial

behavior as previous work by Richard Ebstein pointed to weak correlations between these two

types (Knafo et al., 2011, 58). “Self-initiated prosocial behavior” was examined in three

situations. They included:

1) Helping: Prosocial behavior was coded if the child helped the experimenter pick up

an object that was “accidentally” knocked over (e.g. a pencil box) without having

been requested to do so, and before the experimenter began picking up the pencils.

2) Providing emotional support: Prosocial behavior was coded if the child helped or

comforted an experimenter pretending to have hurt her knee and vocally expressing

pain for 30 seconds.

3) Sharing: Prosocial behavior was coded if the child shared at least one edible/treat

from a pack of treats that were given to both the child and the experimenter after the

experimenter vocalized disappointment that her pack of favorite snacks only had 3

(versus 20 in the child’s).

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“Compliant prosocial behavior” was also examined in three situations. They included:

1) Helping: Prosocial behavior was coded if the child actively helped to look for a finger

puppet that the experimenter “lost” (but was actually hid prior, requiring the child to

actively look for the object in order to find it) after the experimenter requested “Can

you help me find [the finger puppet]?”

2) Providing emotional support: Prosocial behavior was coded if the child behaved in a

comforting manner after the experimenter indicated that her doll was now “very sad

and wanted to cry” and after the experimenter asked the child “Can you help the doll

feel better?”

3) Sharing: Prosocial behavior was coded if the child shared at least one sticker from a

set of 6 sticker sheets given to the child after the experimenter asked “would you

liked to give any stickers to a child you don’t know who has not gotten any stickers?”

(the presence of sharing and the quantity shared were coded).

Prosocial behavior across the six situations were coded to create two prosociality measures:

compliant and self-initiated. In order to increase comparability, the team coded children’s

responses as dichotomous variables (while acknowledging the fact that in most situations the

child’s behavior could be rated on multiple dimensions). Prosocial behavior was coded “1” and

the lack of it was coded “0.” The measures of compliant vs. self-initiated prosociality was coded

on a range of 0-3 (Knafo et al., 2011, p. 58). Additionally, “mother-rated prosocial behavior”

was also assessed via the Strengths and Difficulties Questionnaire. This 25-item questionnaire

asked parents to “identify whether certain behaviors were ‘not true’, ‘somewhat true’, or

‘certainly true’ for their child (Knafo et al., 2011, p. 58). This questionnaire, however, did not

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differentiate between “compliant” and “self-initiated” prosociality.

Assessing parenting style quantitatively

Researchers used the Robinson, Mandleco, Olsen, and Hart (1995) scale to assess

“warmth, induction and reasoning, autonomy support, punishment, verbal hostility, and physical

coercion” (Knafo et al., 2011, p. 58) in parenting style. Researchers felt this particular scale had

good breadth, reliability and validity and specifically chose it for their study. In an additional

assessment, mothers also had the opportunity to describe their behavior toward each twin using a

scale assessing love-withdrawal that was adapted from one of Ariel Knafo’s previous studies

(Knafo et al., 2011, 58). Even still, the researchers had a separate scale to assess for

“unexeplained punishment” (due to their interest in unexplained punishment’s affect on children

with a variant allele of the dopamine receptor D4 also referred to as the DRD4-III

polymorphism). The unexplained punishment scale was kept independent of all other parenting

style scales; the other scales were put through a factor analysis where two factors emerged;

“warmth, induction and reasoning, and autonomy support all loaded positively” on a factor the

researchers termed “maternal positivity” and “verbal hostility, physical coercion and love

withdrawal all loaded positively” on a factor the researchers termed “maternal negativity (Knafo

et al., 2011, p. 58). The two factors correlated moderately negatively (r= -.22p<.01) pointing to

their related but independent aspects of parenting.

D4 gene polymorphism

In order to test for the DRD4-III polymorphism, researchers extracted each twin’s DNA

using a “Master Pure” kit. The “Master Pure” Complete DNA and RNA Purification Kit is

described as a kit using novel technology that enables efficient purification of intact total nucleic

acid (TNA), DNA, or RNA from every type of biological material”

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(http://www.epibio.com/applications/nucleic-acid-purification-extraction-kits). A Polymerase

chain reaction (PCR) test was done to copy and locate the DRD4-III polymorphism on each

twin’s DNA: after this procedure, a chart was created in order to indicate the distribution of the

DRD4-III polymorphism within their sample size.

Key Findings

Interestingly, researchers found no correlation between “self-initiated” and “compliant”

pro-social behavior; this points to the notion that the factors are “substantially different facets” of

children’s prosociality (Knafo et al., 2011, 59). In addition, no linear correlation was found

between mother-rated and observed prosocial behavior, however, highly prosocial children (as

defined as “children who behaved prosocially in at least 5 out of the 6 observational tasks”) were

rated by their mother as more prosocial than other children (M= 1.63, SD= 0.30). Children

performed, on average, 0.53 self-initiated prosocial behaviors (out of the possible 3), but

performed a statistically significant 2.19 compliant prosocial behaviors. On average, girls

performed more compliant prosocial behaviors than boys—a finding that replicated Eisenberg’s

past findings of “higher prosociality in girls” (Knafo et al., 2011, 59). It should be noted that no

significant sex differences were found for self-initiated prosocial behavior.

Genetic and environmental influences on prosocial behavior

The team found that all three measures of prosociality showed “substantial heritability”

but, interestingly, showed differing patterns of genetic influence. Heritability for compliant

prosocial behavior was “modest, accounting for a third of the variance” and indicated an additive

genetic influence (Knafo et al., 2011, 60). Self-initiated prosocial behavior was stronger and

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represented “non additive effects” as was the case for mother-reported prosocial behavior. The

team found interesting results after comparing the twin carriers of the DRD4-III 7-repeat alleles

with DRD4-III 7- absent twins. For 7-abset children, no significant relationship at all was found

between parental style (e.g. positivity, negativity, or unexplained punishment), and any of the

measures of prosocial behavior. When the team looked at the relationship between parenting and

child prosocial behavior of twins with the 7-present allele, however, “mother-rated prosocial

behavior correlated positively with maternal positivity, and negatively with maternal negativity”

(Knafo et al., 2011, 61). Furthermore, the team also found a positive linear relationship between

maternal punishment, and self-initiated prosocial behavior, but again, only with 7-present allele

holders; 7-present children with the most positive mothers were the most prosocial and children

with the least positive mothers were the least prosocial (Knafo et al., 2011, 61). This pattern,

again, points to the effect of differential susceptibility to parenting that has been previously

studied by Jay Belsky, professor of Human and Community Development at UC Davis (Belsky

& Pleuss, 2009).

This study possessed clear methodological strengths. Despite what conventional wisdom

says about the fixed nature of prosociality (an either “you are or you’re not” dichotomy), the

research team was willing to challenge that approach. Their varying and multi-method research

design provided new insight about the nature of genetics’ interaction with environment (in this

case parental style). The testing of children’s prosocial behavior went beyond just questionnaire

from their parents, and included testing out scenarios in the laboratory. Linear regression,

comparisons of associations in the two genotype groups, and intrafamily comparisons of

“discordant genotypes” provided “similar directional results” attesting to the internal validity and

attempt to control contaminating influences. Additionally, the use of very different measures

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(DNA extraction, laboratory observation, and maternal questionnaires) reduced the risk of shared

method variance (Knafo et al., 2011, 65). The limitations that exist in the study entail the

relatively small sample size for a twin study (168 pairs). The researchers’ use of mothers’ self-

report to account for parenting style can also, in some ways, be seen as a limitation. Furthermore,

twin studies design relies on the assumption that both twins were exposed to the same or similar

environments and parenting styles; this is perhaps an unrealistic assumption that can—from

below the surface—lead to the variances we see in siblings, even twins.

The overall findings of the paper provide key insights into the interaction of genes and

environments with plenty of room left for exploration into the phenomenon of differential

susceptibility and gene-environment interaction or “GxE”. One way I would strengthen the

research in this paper to consider using a longitudinal emergent methodological design. I think a

twin study could benefit from this approach because emergent methodology can be a way to

make space for the unfolding and continuing interplay between the data and a developing

interpretation of the data. Illuminating information could be gathered by analyzing whether or

not the linear relationship between parenting style and level of prosocial behavior is steady over

the lifespan of the 7-present child; therefore, a longitudinal emergent methodological design

would be valuable. Additionally, I would seek to expand the definition of environmental

influences (in this case parenting style), and measure other environmental influences such as rate

of exposure to home and community violence, and level of food security versus insecurity and

how it affects self-initiated prosocial behavior in children with the 7-present versus 7-absent

allele. Doing so would give another layer of insight around the nature of motivation for the

prosocial behavior that was seen in 7-present children. At present, researchers are speculating

that because the D4 dopamine receptor is linked to the reward system in the brain, perhaps 7-

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present children are “more sensitive to reward try to avoid punishment as much as possible”

(Knafo et al., 2011, 64). Little is known about why 7-present children are rated higher in self-

initiated prosocial behavior (one hypothesis is that these children “are more alert” and more

attuned to the need to behave prosocially (Knafo et al., 2011, 65). Perhaps this is where the

power of mixed-methodologies for twin research designs can come into play. In addition to

quantitative ways to measure student’s prosocial behavior, researchers may benefit from open-

ended questionnaires, as well as interviews that can generate rich data around children’s

experiences and motivational orientations.

To further strengthen the aspect of this study that looks at differential susceptibility and

variation in the dopamine receptor D4 genes, researchers should work to investigate a robust

sample of non-sibling children carrying the 7-allele polymorphism. Given the results of a clear

linear correlation of prosociality mediated by environment on 7-present children, this study’s

findings should theoretically be generalizable to other 7-present children and youth located, in

this case, in a large city in the Middle East. Because little research has focused on the molecular

biology of prosocial behavior until now, it could be meaningful to compare the development of

children from different communities as a way to understand how environment (even when in

utero) affects molecular development. Do children from families with limited access to adequate

nutrition and water, and living in high-stress neighborhoods have the same core endophenotype

(biological markers) as children living 50 miles away in a safe and well-resourced

neighborhood? Are their endophenotypes different? Perhaps mapping the distribution of 7-allele

polymorphism carriers can illuminate a link or pattern to phenomena in other branches of social

sciences.

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Works Cited

Belsky, J., & Pluess, M. (2009). Beyond Diathesis Stress: Differential Susceptibility to

Environmental Influences. Psychological Bulletin, 135(6), 885-908.

Duke Center for Interdisciplinary Decision Sciences. (2013). D-CIDES: Duke Center for

Interdisciplinary Decision Sciences. Retrieved from: http://dibs.duke.edu/research/d-

cides

Knafo, A., Israel, S., & Ebstein, R.P. (2011) Heritability of Children’s Prosocial Behavior and

Differential Susceptibility to Parenting by Variation in the Dopamine Receptor D4 gene.

Development and Psychopathology, 23 (01), 53-67.

Nucleic Acid Purification - Extraction Kits (2011). Nucleic Acid Purification - Extraction Kits.

Retrieved from: http://www.epibio.com/applications/nucleic-acid-purification-extraction-

kits