Understanding the Effects of Genetics and Environment on Behavioral Differences

 ("Genes and Environment")

Are the behavioral differences between introverts and extroverts moreso due to genetics or environment?  In my prior post, I explained that genetics and environment may contribute equally to behavioral differences in individuals, and that most traits are due to one or the other.  After sitting down with my mentor, Dr. John Peles, who teaches behavioral genetics at Penn State University, Greater Allegheny campus, I have gained a better understanding of the subject and how it relates to the differences between introverts and extroverts, as well as the methods through which human behavior is tested for genetic and environmental influences.  Dr. Peles explained to me that most human behavioral traits are actually found in genetic coding, but that they can still be influenced by environment.  In fact, he described that, in the case of most behavioral traits, genetics has fifty-percent, or half, of the influence, while environment has the other fifty-percent, or half, of the influence.  In other words, he explained to me that, in most cases, humans are genetically predisposed to certain behavioral traits (such as those linked to introverts and/or extroverts), but that environment still plays a key role in determining the expression of said traits.  Referring to such relationship as a "genotype-environment interaction" (genotype is defined as genetic makeup), Dr. Peles described that in some cases, our genotypes influence how we respond to situations, but the situation itself sometimes changes how we respond to subsequent similar situations.  As a disclaimer, genetics and environment do not always play equal roles in determining expression of human behavior - in some cases, genetics and instinct override environmental influences, while in others, environment overrides genetics and instinct - but on average, this fifty-percent rule holds true.  This helps to explain the behavioral differences between introverts and extroverts, for it appears that both genes and environment determine which group an individual associates with.  In many cases, an individual who is genetically predisposed to being an introvert or extrovert (based on stimuli need or pure behavioral encoding) will place themselves in a situation that is conducive to their needs and comfort.  This factor, which is also an attribute of the "genotype-environment interaction," can push individuals further into their respective categories as introverts or extroverts.  However, in some cases, individuals become introverts or extroverts as a result of "pure environment."  For example, an individual may be genetically predisposed to being an extrovert, as they require more stimuli than a genetically predisposed introvert, but because of an embarrassing event or social ridicule, they may be pushed to become an introvert.  As another example, an individual may be genetically predisposed to being an introvert, as they require less stimuli than a genetically predisposed extrovert, but because of attention received through peers, they may be pushed to become an extrovert by accepting the situation and appeasing said peers.  On a different note, Dr. Peles and I also examined the different methods through which researchers determine whether a behavioral difference is influenced by genetics or by environment.  This research was necessary for the fact that I may employ similar methods later in my own research in the field, as well as for the reason that I should generally understand how researchers have determined phenomenon such as the aforesaid fifty-percent rule.  Most experts studying the influences on behavioral differences either a method called the "sibling approach" or a method called the "adoption approach."  In the case of the sibling approach, researchers compare behavioral differences between individual siblings and between individual twins, searching for any attributes that may be due to genetics.  Because siblings generally grow up in the same environment, as they are raised in the same household, it is believed that most of the behavioral differences that they exhibit will not be due to environment.  Rather, by comparing such behavioral differences against pairs of monozygotic twins, who both are exposed to the same environment and genes, researchers can determine to what scale certain genes predispose individuals to behavioral traits.  In the case of the adoption approach, researchers investigate behavioral differences between pairs of twins who have been exposed to different families.  If the twins were separated at birth, so long as they are identical and monozygotic, they will have the same genes, but not the same environment.  Thus, researchers can determine if behavioral traits are due to environment by looking at the behavioral differences exhibited by separated identical twins.  Overall, by understanding how behavioral genetics and the influence of environment works, we can logically explain the behavioral differences between introverts and extroverts.  In my next post, I plan to look at some specific examples in which introverts and extroverts show signs of genetic or environmental influence in their behavioral differences.

As this graphic illustrates, most behavioral traits in an individual are a result of a combination of nature (genes) and nurture (environment), as well as individual choices ("Nature? Nurture? Neither? More?").

Also, for an update on my survey, I believe that the one that I previously posted should be sufficient for the beginning stages of this study, so I plan to be distributing it soon to classrooms, throughout communities, and online.  Please keep a lookout for it in the coming weeks; I would greatly appreciate it if you could fill it out when it becomes available so that I can begin some data studies.


Works Cited:
"Genes and Environment."  Academic Help.  Academic Help, 6 Oct. 2014.  Web.  4 Dec. 2014.
"Nature? Nurture? Neither? More?"  PhD in Parenting.  Squarespace, 15 Dec. 2010.  Web.  4 Dec.