the rats’ physiological makeup.
A pattern was emerging. The rat pups’ parents’ behavior—the pups’ environment, their nurturing—was affecting their very nature.
In order to make sure it was the actual behavior of the parents that became part of the genetic code, and not something permanently inborn, Meaney switched pups at birth and had them raised by a different kind of licker, and lo and behold, pups conformed to the kind of care they received from their foster parents, even carrying their newly taught high- or low-licking responses to their pups when they had them.
* * *
—
IN A 2019 editorial called “Healthy Parenting in the Age of the Genome: Nature or Nurture?” Saoud Sultan explains that environment does not change DNA; rather, “epigenetics refers to the role of environmental factors on gene activation or silencing, without changing the DNA nucleotide sequence.” He adds, “Maternal behavior is also considered to be transmitted in this manner across generations.”
How does this happen? Through a complex interplay of our environment and our bodies:
Studies in both animals and humans have shown that the quality of parenting is affected in mothers who had received poor care during childhood. Hormones play a significant role in maternal behavior. However, for example, levels of oxytocin, which stimulates and maintains maternal behavior, have been found to be lower in mothers with insecure attachment after interaction with their infants than mothers with secure attachment. In addition, adverse parenting received during the early years of life negatively influences women’s brain morphology, such as the hippocampus, as well as maternal brain activations to child stimuli, such as in the hippocampus, nigrostriatal pathways and insula.
While wise scientists (and writers about science) usually resist the urge to make connections between, say, rats and people, animal studies can serve as windows into an aspect of our own behavior, if not exact replicas. As Swiss scientist Marialuigia Spinelli wrote in 2017, “Intriguingly the results of Mean[e]y’s [rat] experiment appear very similar to John Bowlby’s ethological theory of attachment.” She goes on to describe the social-releasing, back-and-forth process of a sensitive caregiver attuning to an infant’s signals as “the basis on which the child develops…a set of [attachment] behaviors that help keep the caregiver nearby in order to be protected and supported while exploring the environment.” In other words, the co-regulation that happens between baby and caregiver is like the grooming and licking that helps cue attachment epigenetically, i.e., through the impact environment has on genes.
Spinelli goes on: “It can be argued that this spectrum of [secure-base] behaviors descripted by Bowlby [and Ainsworth!] is the consequence of the epigenetic footprint provided by mother [caregiver] to offspring,” which means that we learn how to be sensitive not just by way of the gaze we receive when our parents look at us, but because it becomes expressed through our genes.
While epigenetic experiments are tricky to perform on people, in that they require shifts in environment radical enough to test the impact on one’s genetics, there is a naturally occurring “experiment of opportunity” that has been studied by attachment researchers: foster care, the common practice of children being raised by people other than their biological parents. And indeed, the latest research on foster parents found that the correlation between a foster infant’s Strange Situation and the foster parent’s state of mind was 72 percent, almost exactly what is found in biological families. The authors of the study believe that “these data argue for a nongenetic mechanism for the intergenerational transmission of attachment,” which is to say, what we do matters. Big-time. But what we do is not just a list of behaviors. It’s a way of being. And being is anything but simple.
As one scholar writes:
It should be noted that although extensive studies have been conducted to determine the epigenetic influences on maternal behavior, there have been inconsistent results, and thus this research area has remained complex. Furthermore, it is difficult to ascertain the extent to which parenting behavior is influenced by epigenetics alone and to analyze this separately from the influence of environmental factors. Therefore, it is challenging to integrate the genetic and environmental principles and identify all factors that influence the processes