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A note for Lesson no. 3, "Little Brains Wire Themselves to Their World," in Seven and a Half Lessons About the Brain by Lisa Feldman Barrett.
Some context from page 48 is:

To a remarkable extent, a baby’s genes are guided and regulated by the surrounding environment.

Brain development is a constructive process — it is not a pre-programmed unfolding of what is written in the genes. The environment provides inputs that guide genes for normal development, such as the need for retinal input mentioned in this lesson. The field that studies how the environment guides and regulates gene expression is called epigenetics.[1][2]

Your entire body, including your brain, is made of proteins. The recipes for these proteins are found in genes (for an accessible explanation, see Mukherjee, 2016).[3] Having a gene does not guarantee that you will make its associated proteins, however. (See the appendix entries for lesson no. 1 for homology and genes.) Environmental input is also crucial. In fact, most of your genetic material (your genome) makes the chemical compounds that are devoted to regulating the 5% that actually contains the recipes for making proteins, largely under the influence of the environment. The chemical compounds that attach to your DNA to turn genes on and off are called your epigenome. You have genes that regulate how much impact the environment can have on your other genes.[4]

For humans, genes are transcribed and therefore the brain and the body are forged within an environment that is shaped by other humans, a topic we visit in lesson no. 7. [5] Part of what we think of as “heredity” or “hard-wiring” is the result of consistent and repeated inputs that come from an environment that is constructed and maintained by other people, including an infant’s caregivers.[6]


  1. Jablonka, Eva, and Marion J. Lamb. 2014. Evolution in Four Dimensions: Genetic, Epigenetic, Behavioral, and Symbolic Variation in the History of Life. Cambridge, Massachusetts: MIT Press.
  2. Lewontin, Richard. 2001. The Triple Helix: Gene, Organism, and Environment. Cambridge, MA: Harvard University Press.
  3. Mukherjee, Siddhartha. 2016. The Gene: An Intimate History. New York: Scribner.
  4. Caspi, Avshalom, Ahmad R. Hariri, Andrew Holmes, Rudolf Uher, and Terrie E. Moffitt. 2010. "Genetic Sensitivity to the Environment: The Case of the Serotonin Transporter Gene and Its Implications for Studying Complex Diseases and Traits." American Journal of Psychiatry 167 (5): 509–527.
  5. Richerson, Peter J., and Robert Boyd 2006. Not By Genes Alone: How Culture Transformed Human Evolution. Chicago: University of Chicago Press.
  6. Badyaev, Alexander V., and Tobias Uller. 2009. “Parental Effects in Ecology and Evolution: Mechanisms, Processes and Implications.” Philosophical Transactions of the Royal Society B: Biological Sciences 364 (1520): 1169–1177.