J. T. Fuller | August 2, 2021
Genes form behaviors through their expressions as modified by epigenetic marks. Genes provide the blueprint for human behaviors, but those plans can be modified through epignenetic expressions. The nurture versus nature question, whether behavior is determined by genes or the environment, has been pondered by many; modern thinking has evolved to a resounding “yes.”
Gene expression does not guarantee a specific behavioral outcome. The study of these variable outcomes is epigenetics, where differences in gene expression is studied in the context of environment and experience. DNA interacts with smaller molecules, called epigenetic marks, that have the ability to turn genes on and off. Genes are expressed when the DNA is read and transcribed into RNA, and translated into proteins by ribosomes. Proteins largely determine a cell’s characteristic and function, and therefore have the potential to impact every part of a person’s existence and behavior. Genes influence behavior by providing the instructions for the body to follow, but there is some interpretation of these instructions.
Twins are often studied because they have identical genes or, in the case of fraternal twins, as close to the same environment as possible without being genetically the same. Twins have the same genetic code, but we see in time they don’t end up in the same condition because of external factors. On a genetic level, these variations in expression are attributed to epigenetic marks, which influence gene activity. These epigenetic markers are sometimes passed down from parents (although most are erased when the sperm and egg come together), otherwise come from the external environment.
Genes control behaviors to the extent they provide a starting point for behavior. There are other factors beyond genes that interfere along the way, such as inherited epigenetic marks and environmental factors. Twins have been studied extensively to better understand how far genes reach in controlling behavior, and one study showed by age 50, identical twins were as epigenetically different as non-twin siblings are in childhood. That is to say that there are many intervening factors between genes and the ultimate displayed behavior, such as trauma, drugs, disease, or chronic stress.
For example, a stress-protective gene in rat pups is activated when raised by nurturing mothers, but rat pups with inattentive mothers do not have this gene activation and experience a stronger stress response later in life. An interesting study on the cloning of working dogs highlights how even with genetically identical dogs, trainers appear to be able to train suitable dogs 80% of the time or more from clones, whereas the average litter is expected to contain 20-40% suitable dogs. This suggests that if the environment is held reasonably constant, identical genes will largely display in the same way even if raised apart. However, the genetic traits do not develop in a vacuum and will always be impacted by the environment in some way.
The nurture versus nature debate has been argued for a very long time, but earned its moniker in 1871. Contemporary research is more focused on how nurture and nature work together rather than which is responsible. Neither is able to create behavior alone and both are involved with the ultimate display of gene-based instructions.
In conclusion, genes are at least partially responsible for human behavior, but not completely. Genes do control human behavior, but only like a recipe book where the cooking still needs to be done. Human behavior is dictated by both genetic material and the person’s environment, which work inextricably together.
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TED-Ed. (n.d.). What is EPIGENETICS? - Carlos Guerrero-Bosagna. TED. https://ed.ted.com/lessons/how-the-choices-you-make-can-affect-your-genes-carlos-guerrero-bosagna#watch.
Branwen, G. (2018, September 18). Dog Cloning For Special Forces: Breed All You Can Breed. Gwern.Net. https://www.gwern.net/Clone#clone-success-rates
Mcleod, S. (2018, December 20). Nature vs. Nurture in Psychology. SimplyPsychology.org. https://www.simplypsychology.org/naturevsnurture.html
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