Applied Psychology OPUS

Epigenetic effects of Maternal Behavior... Sounds a lot like Attachment Theory

by Sammy Ahmed

         In the realm of human development, there is large debate as to whether “nature” or “nurture” is more influential to various aspects of human development. The field of developmental psychology recognizes both nature and nurture as deterministic forces, however, places a large emphasis on the influences associated with “nurture”, providing evidence that the postnatal family environment is the primary force in the development of individual differences in personality (Zhang & Meaney, 2010). On the other hand, developmental biologists tend to view human development with a “nature” lens. For example, biological or evolutionary approaches understand the brain and its development as being subject to evolutionary forces outside of immediate environmental factors. Additionally, geneticists provide evidence that variation in behavior is merely variation in DNA sequence (Zhang & Meaney, 2010). Although these two opposing perspectives make the umbrella field of human development very dynamic and comprehensive, the emerging field of epigenetics has the potential to unite these two disciplines and provide a unified understanding of human development.

        Epigenetics is a field of evolutionary biology that focuses on non-heritable modifications in genetic material and the various factors that can alter gene expression (Lillycrop et al., 2007), such as DNA methylation. When regions of genes are methylated, the factors necessary for expression are inhibited. Conversely, the de-methylation of gene regions enhances gene expression (Henckel, Toth, & Arnaud, 2007). In other words, DNA methylation causes certain genes to be “turned on or off” without changing the actual DNA sequence (Moalem & Prince, 2007). To get a better understanding of how epigenetics works, consider the famous ‘skinny brown mouse study’ at Duke University. During this study, a team of scientists utilized fat yellow mice to test their epigenetic hypothesis (Moalem & Prince, 2007). These fat yellow mice typically gave birth to fat yellow mice because of a gene called agouti, which gave them the chubby/yellow characteristics (Moalem & Prince, 2007). However, when the treatment group was fed a different diet, they gave birth to skinny brown mice. Interestingly, when analyzing the skinny brown mice’s genetic code, the researchers found that the agouti gene was still present but the characteristics the gene provided were no longer apparent (Moalem & Prince, 2007). The researchers deduced that altering the maternal mouse’s diet caused the gene to be turned off. In other words, the new diet, which included “methyl donors” triggered the methylation of the agouti genes and suppressed the gene, which led to skinny brown mice (Moalem & Prince, 2007).

        Shortly after the ‘skinny brown mouse experiment’, the field of epigenetics exploded. It was evident that genetic sequence is not set in stone and environmental factors can alter the expression of certain genes. Just a brief overview about genetic coding and expression, the genetic make-up/code is called genotype, this determines the genes that are acquired but not necessarily the genes that are expressed; the expression of genes is called phenotype (Mustard, 2010). For instance, identical twins have the same DNA (genotype) but oftentimes will have different experiences, which leads to differences in gene expression (phenotype). Studies reveal that identical twins can have a 30% difference in behavior as adults. According to the epigenetic theory, this difference is likely to be related with the epigenetic affects in early development (Mustard, 2010). There have been numerous studies examining epigenetic effects on various psychological outcomes. For example, studies have revealed that epigenetics could be a factor in schizophrenia, bi-polar disorders and Attention Deficit Hyperactivity Disorder (Mustard, 2010).

        Whereas the ‘skinny brown mouse experiment’ showed how factors before birth could affect the offspring’s characteristics, studies have also shown that epigenetic modifications can occur after birth. In fact, a study at McGill University set out to examine whether there could there be epigenetic changes after birth. According to Meaney & Szyf (2005), the interaction between mothers and their offspring could provoke epigenetic changes in their offspring’s phenotypes. The results of their experiment reveal that when baby rats received different levels of attention from their mothers, they grew up with relatively different temperaments. Rats who received more attention from their mothers shortly after being born grew up to be relaxed, sociable and handled stress better than their attention deprived counterparts, who grew up to be nervous and more susceptible to stress (Meaney & Szyf, 2005; Moalem & Prince, 2007). To rule out genetic effects, the researchers switched the baby rats; they gave the baby rats from mothers that tended to be less attentive to more attentive mothers. Regardless of the biological mother, the babies who received more maternal care, grew up to be well-adjusted and had ‘better social skills’ (Moalem & Prince, 2007). Furthermore, the follow-up gene analysis revealed that the rats that received more maternal attention had a decrease in methyl makers of the genes associated with brain development, so the researchers concluded that the maternal care removed the methyl markers that would have otherwise caused their nervous temperament (Moalem & Prince, 2007).

        Interestingly the results of Meany’s experiment appear very similar to John Bowlby’s ethological theory of attachment. The ecological theory of attachment was established in 1969 and has been a prominent theory in developmental psychology, as it attempts to understand how the infant-caregiver bond is related to the child’s feelings of security, emotional development and future relationships. The notion of establishing a secure attachment to the primary caregiver is paramount to this theory and is linked to various social and emotional outcomes. During the pre-attachment phase (birth-6 weeks), having an attentive caregiver is crucial to the establishment of this attachment, as it helps newborns feel connected and comforted (Berk, 2009). According to Sroufe (2005), children who had secure attachments to their caregivers displayed higher levels of self-esteem, social competence and empathy than children with insecure attachments during preschool. When tested again at age 11, the children who had secure attachment to their primary caregiver, displayed better social skills and closer relationships with peers; these children continued to benefit from their secure attachments as children throughout their adolescent and adult years (Sroufe, 2005).

        Although epigenetic principles have revealed some important findings as they relate to psychological development, the challenge lies in integrating genetic and biological principles into a very environmentally based discipline, such as developmental psychology. The findings do not necessarily contract the fundamentals of environmental influences on psychological processes and development; however, reveal how genetics and the environment interact with each other and, together, play a large role in human development. To adopt a holistic approach, is to better understand the dynamics of human development and is crucial in moving forward in both biologically and environmentally based disciplines.


Berk, L. E. (2009). Child development (8 ed.).
Boston, MA: Pearson Publishers.

Henckel, A., Toth, S., & Arnaud, P. (2007). Early mouse embryo development: Could epigenetics influence cell fate determination? Bioessays, 29(6), 520-524.

Lillycrop, K. A., Slater-Jefferies, J. L., Hanson, M. A., Godfrey, K. M., Jackson, A. A., & Burdge, G. C. (2007). Induction of altered epigenetic regulation of the hepatic glucocorticoid receptor in the offspring of rats fed a protein-restricted diet during pregnancy suggests that reduced DNA methyltransferase-1 expression is involved in impaired DNA methylation and changes in histone modifications. Br Journal of Nutrition, 97(6), 1064-1073.

Meaney, M. J., & Szyf, M. (2005). Maternal care as a model for experience-dependent chromatin plasticity? Trends in Neuroscience, 28(9), 456-463.

Moalem, S., & Prince, J. (2007). Survival of the sickest: The surprising connections between disease and longevity. New York: HarperCollins Publishers.

Mustard, J. F. (2010). Early brain development and human development. Encyclopedia on Early Childhood Development. (Published online February 17, 2010)

Sroufe, L. A. (2005). Attachment and development: A prospective, longitudinal study from birth to adulthood. Attachment and Human Development, 7, 349-367

Zhang, T., & Meaney, M. J. (2010). Epigenetics and the environmental regulation of the genome and its function. Annual Review of Psychology, 61, 439–66. doi: 10.1146/annurev.psych.60.110707.163625

Author's Biography

Sammy Ahmed is a senior in the Applied Psychology honors program. He works with Dr. Selcuk R. Sirin on The Meta-Analysis of the Immigrant Paradox Project (MAP) and The New York City Academic and Social Engagement Study (NYCASES). Sammy has recently been awarded the Outstanding Research Contribution Award for his honors thesis and his work with Dr. Sirin, as well as the Founder’s Day Award. He will also be Applied Psychology’s Banner Barer at this year’s Baccalaureate Ceremony. His research interests lie at the intersection of psychology and medicine, with an emphasis on the psychological and socio-cultural triggers for disease. He will be attending Harvard University next fall to continue his pre-medical studies, with the ultimate goal of attaining an MD/Ph.D.