Friday, March 13, 2015

Nature vs. Nurture: Potential Physiological Differences in Adoptees

Theories of ‘nature vs. nurture’ have been debated since before the turn of the nineteenth century, but professionals have yet to come to a consensus regarding the matter.  Perhaps one of the best ways to study this phenomenon is by assessing and analyzing adoptees.  If either nature or nurture were to have a distinguishably significant impact on character development, the changes would be most evident in individuals who were raised by people other than their biological parents, allowing for the separation of genetic and environmental factors in the evaluation of their impact.

Various studies have been done to analyze the role of adoption in child development, including studies regarding domestic and international adoption.  Research groups such as van Londen et al.[1] have demonstrated that the majority of internationally adopted infants are able to form familial bonds of secure attachment following adoption. In addition, adolescent and young adult adoptees have been studied regarding social performance and externalization of behavior following cognitive maturation. One of the longest studies analyzing the development of adopted children through young adulthood is the Colorado Adoption Project (CAP)[2], which has longitudinally studied behavioral development of adoptees since 1975.  In this study, there are two divisions of the analysis: Classic CAP, with subjects of ages 0-16, and Current CAP, of subjects of ages 17 until now.  The studies of the CAP investigate 
externalized effects on adopted subjects, such as relationships, milestones, and education.

While studies of adoptees in their behavioral tendencies have been done for a while, it was not until recently that studies were conducted regarding the physiological changes and variations in reflexive responses to stimuli.  These types of studies arguably fit into the ‘nature’ category of the nature vs. nurture debate.  Schoenmaker et al.[3] explores the influence of adoption experience on basic physiological reflexes that are expected in young adults. The group looked at various aspects of normal maternal/paternal instincts of adoptees, including attachment security, perceived urgency, and respiratory sinus arrhythmia in the subjects.  These variables were assessed with relation to a cry paradigm, designed by the researchers to evoke certain reactions from the participants.  The most remarkable impact identified was the ‘secure’ and ‘insecure’ attachment classification of the individual. It was ultimately deemed that insecure attachment adoptees responded with significantly lower urgency to the cry paradigm than securely attached adoptees; furthermore, what can be described as a “higher tolerance” for infant distress, decreasing the likelihood of a response. 

In order to understand what the above conclusions are suggesting, it is necessary to distinguish between secure and insecure attachment in individuals.  Secure attachment, as outlined by Schoenmaker et al., secure attachment is rooted in a consistent base of support beginning in the early developmental ages, instilling the confidence that support will be there.  In contrast, an insecurely attached individual is someone who lacked consistent and coherent support at a young age, and is therefore less motivated by personal relationships and less likely to support others.  Based on these definitions, along with the adoptee status of participants, it can be argued that this is caused by nurture. 

The difficulty in determining whether the differences between securely and insecurely attached adoptees stem from nature or nurture lies in the juxtaposition of the explanations as to why the distinction occurs.  The potential difference in physiological changes based on attachment representation addresses the involvement of the parasympathetic nervous system in emotional and physiological response to attachment stimuli (ie, the cry paradigm).  The decreased emotionality displayed by the insecurely attached individuals supports a distinction between secure and insecure adoptees. 

Studies of adopted individuals such as this one performed by Shoenmaker et al. inform and suggest theories that could be useful to further research.  However, the clinical analysis also adds another layer of complication to the nature vs. nurture debate.  How can someone classify one way or the other when both mechanisms have such an influence on the individual? This article reinforces the battle between nature and nurture, which highlights the difficulty in coming up with a decisive explanation.  Many people interpret lack of concreteness to be an indication of a marriage between the two theories. Regardless of the medical, evolutionary, and scientific advances that have been made in the past century, each study and article regarding human psychological development adds complexity to the ongoing debate of ‘nature vs. nurture’ – a debate that does not appear close to being resolved.

[1] Londen, W van (11/2007). "Attachment, cognitive, and motor development in adopted children: short-term outcomes after international adoption". Journal of pediatric psychology (0146-8693), 32 (10), p. 1249.
[2] Rhea, S.-A., Bricker, J. B., Wadsworth, S. J., & Corley, R. P. (2013). The Colorado Adoption Project. Twin Research and Human Genetics : The Official Journal of the International Society for Twin Studies, 16(1), 10.1017/thg.2012.109. doi:10.1017/thg.2012.109
[3] Schoenmaker, C., Huffmeijer, R., van Ijzedoorn, MH., Bakermans-Kranenburg, M.J., van den Dries, L., Linting, M., van der Voort, A., & Juffer, F. (2014). Attachment and physiological reactivity to infant crying in young adulthood: Dissociation between experiential and physiological arousal in insecure adoptees. Physiology & Behavior. pp. 549-556. Elsevier. *Main article on which this post was based


  1. I think the debate between nature and nurture is fascinating and find it compelling that some adopted children are insecurely attached while others are securely attached. It seems that the nature with which they were born (poverty stricken village in Vietnam vs. a US house) before being adopted plays a big role in effecting their development, but also the way they are nurtured by the parents who adopted them. It seems these two factors go hand and hand, which I think is intriguing. Also I think it is cool that the level of nurture, and support, given to a child will not only impact their development, but impact the level of support that they, in turn, give to their kids. Nurture level given from parents seems to be stay the same from generation to generation as a sort of cycle.

  2. This post does a great job at showing the complexities of the nature v. nurture argument. It shows the behavioral tendencies of adoptees depending on the support they received as children. While the secure and insecure attachment influences an adoptees tendency to cry, it does not account for hereditary factors that may influence an adoptee’s development. Considering that “tendency to cry” is a personality trait, one should consider that personalities can be attributed to genetic factors that are passed down. These genetics factors, however, are impacted by environmental factors; therefore, I believe that our development as people involves a complex interaction of both, nature and nurture. In order to better clarify the separation of genetic and environmental factors, it would be interesting to look at identical twins.

  3. There has always been the nature vs nurture debate. With adoptees and their attachment, I think part of it has to do with the age in which they are adopted. I think that children that are adopted at a very young age and receive a lot of attention from their adoptive parents will become attached to them opposed to those who are adopted at a later age or receive more attention from a nanny rather than their adoptive parents. Also, there is a chance that the environment they were in before can effect the way that they bond with others. If they witnessed very traumatizing events, then that would have an effect on their behavioral tendencies. Following adoptees for a period time would be a very interesting thing to be involved in.

  4. One point of conflict I have with the paper is that it's really hard to separate the effects of nature versus nurture. Without an identical twin to compare to, there's really know way of knowing for sure is there? Also, I wonder how the adopting parents' attitudes might change the child's physiology. That might drastically change adopting criteria.

  5. I've always thought those who boil down changes in our physiology to "nature vs. nurture" aren't seeing the full picture. Both effect us, and those who say otherwise are simplifying it and ignoring the complexities of the world. I have certain traits because genetically they were passed down to me. Genes can determine intelligence, personality, and emotions to an extent. But these things are also shaped by our experience, how our caregivers treat us, and our education. I think boiling it down to an "either/or" doesn't respect the complexity of what makes us individuals.

  6. I think these studies would be improved by having a genetic control for each subject... an identical twin! There have been studies using identical twins that were separated at birth, and I think these studies might hold more weight in their arguments than the current one. Nonetheless, this research is interesting!

  7. This post reminds me of correlational research showing that mothers of securely-attached babies have parenting styles that are more responsive and sensitive to the baby's needs. A study (Van den Boom 1994) suggested that naturally cranky/irritable babies are more difficult to raise, resulting in reduced sensitivity of the parent which leads to insecure attachment. This hints on the interaction between "nature" (basic personality variation among infants) and "nurture" (parenting style) on attachment development, and I think it is promising for adoption because it shows that good parenting style can shape secure attachment, at least to some extent.

  8. I agree with Haley, I would think that the age of adoption would play a large role in the relationships that they form with their adoptive parents. I also agree with Max's comment in that how are researchers able to compare adpotees when there are so many differences between each of them. I would like to see a study that assesses identical twins that are raised in different environments (basically, recreate "The Parent Trap"). I think a lot of people would be more inclined to believe that nature v. nurture is a real thing if identical twins were compared because there is only one possible explanation for the differences observed.