The “Nurtured Genetics” Hypothesis: Prenatal Testing and The Anchoring of Genetic Expectancies

If polygenic risk scores for traits are to be provided to parents before --as opposed to after -- a child is born, these scores will provide the very first units of information upon which parents will begin to form an impression of their child. On the basis of this distinction, we draw from research in social psychology we formulate three sequential hypotheses that build on each other to conceptualize and introduce the “nurtured genetics” effect along with the psychosocial implications it entails.

• 1)Presenting polygenic scores for traits as the first units of information about a child will lead parents to assign undue weight to that genetic information (primacy effect).
• 2)Parents informed about a future child’s genetic predispositions (before birth) will form “genetic expectancies” (i.e., expectations created on the basis of polygenic scores), and will be less amenable to updating those expectancies based on subsequent environmental information compared to those informed post-birth (anchoring and adjustment heuristic).
• 3)Parents will search to confirm or disconfirm their genetic expectancies and in doing so, they will be exposing their child to environments conducive to the actualization of their genetic expectancies.

Nature first, Nurture second: Primacy Effects

Extensive research from the field of Social Psychology has demonstrated ways in which the order and context in which information is presented can influence the way people interpret and use such information. For example, the mere order in which people process and evaluate a list of personality traits can influence the general impression they form of a particular individual (Sullivan et al 2019). For example, Solomon Asch (1946) conducted a study in which participants were asked to form an impression of an individual based on a list of personality traits. Some participants were presented person A, while others were presented person B, both were asked to form a general impression of the person they evaluated:

Person A: intelligent–industrious–impulsive–critical–stubborn–envious

Person B: envious–stubborn––critical –impulsive–industrious– intelligent

The results demonstrated that person A was evaluated more positively and person B was evaluated more negatively. Interestingly, A and B are the same person – they have the same personality traits - only the order in which positive and negative traits were presented was reversed. The differences in the two impressions are driven by a primacy effect whereby initial information is being weighted more heavily than the subsequent information. The mind processes and assimilates new information in reference to existing knowledge, so secondary information tends to be appraised congruently with the primary information. We use the anchoring and adjustment heuristic to hypothesize how initial (genetic) information is likely to influence the way parents will process subsequent (environmental) information.

Due to advances in personalized genomics, it has become possible to quantify genetic variance and use it as an individual source of information. Polygenic Scores (PGS) are probabilistic scores that can provide information about an individual’s genetic likelihood of developing any (conceivably measurable) phenotypic trait. (i.e., extraversion, intelligence, height…etc.). Not only is genetic variance quantifiable and accessible as a source of information, but it can also precede most sources of environmental variance through prenatal testing. That is, parents can receive probabilistic genetic scores as the very first piece of evaluative information about their child. This genetic information will precede any (observable) environmental influences on their child’s development, and it is upon these initial probabilistic genetic estimates that they will create expectancies as to who their child will become and how they will behave. The concern is that polygenic scores - which only account for a relatively small portion of individual behavioral variability (see Plomin & Von Summ 2022 for recent PGS estimates) - will lead parents to over-value genetic information over subsequent environmental information in forming an initial impression of their child.

Genetic Expectancies: Anchoring and Adjustment

We further hypothesize that these genetically informed priors (i.e., initial impressions formed on the basis of PGS) can, in turn, anchor parents’ expectancies, and on the basis of these genetic expectancies parents will come to assimilate subsequent environmental (behavioral) information in a genetic confirming manner (Miller and Turnbull 1986; Roese and Sherman 2007). The concern is that the genetically informed priors will anchor parents’ expectancies and lead them to insufficiently update their expectancies when encountering environmental information (Eply and Gilovich 2006; Hogarth and Hillel 1992). However, it is important to note that first impressions and their resulting genetic expectancies are malleable. Parents will naturally start to update their genetically informed priors at some point when they are faced with sufficient environmental evidence. But, the primacy effect, anchoring their genetic priors, would require considerably more evidence to update the initially formed impression.

The Nurtured Genetics Effect: A self Fulfilling Prophecy

The most concerning outcome of prenatal genetic testing may result from parents simply wanting to test the veracity of their expectancies – do their children really behave congruently to their genetically informed expectancies – and in so doing expose them to environments conducive to confirming those expectancies. Research studies examining the influence of teacher expectations on student behavior have demonstrated that expectancies, induced on the basis of randomly assigned test scores, could lead to self fulfilling prophecies whereby the teacher’s expectations unintentionally shaped the student’s environment, which ultimately drove the student to behave in accordance with their initial expectations (Rosenthal and Jacobson 1968). A meta-analysis of four studies on self fulfilling prophecies, in which teachers had no prior experience with the student, estimated the effect of teacher expectancies on student IQ to be d=.43 which translates to a difference of 6.45 IQ points (Raudenbush 1994; Jussim and Harber 2005). Furthermore, Raudenbush (1994) found that the effect of expectancies was curvilinear. That is, expectancy effects were found to be particularly pronounced when teachers just began forming an impression of students, but when teachers already knew the students for a certain amount of time, the expectancy effects weakened to the point of vanishing. These findings point to the alarming contextual similarities of prenatal testing, where the child is yet to be born and parents receive polygenic scores as the first units of information upon which they form an impression and therefore provides a context ripe for particularly strong genetic expectancies about their child.

On the basis of genetic scores presented to them, some parents will place their children in environments conducive to confirm or disconfirm their genetic expectancies. For example, exposure to particular environments (e.g, book club vs baseball), selected on the expectation created by a polygenic score (e.g, higher/lower intelligence or higher/lower physical ability), provides the opportunity for a parent to confirm whether their child behaves in such a way (e.g., intellectually or athletically), but in doing so they expose their child to an environment conducive for them to develop that particular trait. Selectively exposing a child to a particular environment may have a greater influence on the expression of their behavioral traits than their initial genetic predisposition for those behavioral traits. For example, research on polygenic embryo screening estimates the effect of embryo selection strategy on intelligence (IQ) to be quite small and imprecise - a predicted mean gain of 2.5 IQ points with a confidence interval of ±27 points (Karavani et al 2019). The IQ gain from the polygenic embryo screening selection strategy (2.5) is 2.5 times smaller than the mean IQ effect of expectancies (6.45) derived from the meta-analysis on self-fulfilling prophecies. Even if the effect sizes for the self-fulfilling prophecies were to be inflated (see Jussim and Harber 2005 for review), they are still likely to be at least comparable to the effects of embryo selection.

The effects of differential environmental exposures onindividual behavioral variability should not be underestimated. For example, a study conducted on genetically identical (clonal) fish – separated immediately at birth into identical environments – found that behavioral variability emerged on the first day of life and gradually increased over developmental time (Laskowski et al 2022). If individual behavioral variability emerges under such controlled conditions in species and environments much less complex than our own, we must carefully consider the costs of presenting polygenic scores as the primary source of predictive behavioral information. Especially when these scores may come to shape our environment in a way that fulfills the genetic predictions.

In conclusion: the nurtured genetic hypothesis predicts that exposure to genetic predispositions will create genetic expectancies, which in turn, will selectively expose an individual to environments conducive to confirm the predicted genetic effects. We further hypothesize that the strength of nurtured genetic effects is curvilinear to the timing of exposure to the genetic information. Therefore, parents who undergo prenatal testing are predicted to elicit particularly stronger nurtured genetic effects.