The Science Behind It All...The Differences Between Introverts and Extroverts Biologically

Introverts and extroverts have been shown to differ in brain processing and function.  This difference may also be the underlying factor for their overall behavioral differences.  (Jarrett)

Over the past few months, I have explored what the behavioral differences between introverts and extroverts are, and I have debunked some myths/fallacies regarding the two groups.  Moreover, I have addressed some of the reasons and factors behind these behavioral differences, those being environment, base arousal level, and genetics.  However, I do not feel as if I have thoroughly explained what really causes an individual to be an introvert or an extrovert, or what causes their typical behavioral differences.  One of the leading causes in this phenomenon is difference in brain processing.  Introverts and extroverts have been found to register and process information differently, which likewise can lead to their differences in behavior.

This is a sample of what a PET (positron emission tomography) scan might look like, with the different colors representing different levels of brain activity.  ("Positron Emission Tomography Facilities Through Imperial Consultants")

According to Debra Johnson, Ph.D., from the University of Iowa, and John S. Wiebe, Ph.D., from the University of Texas, there is a correlation between personality and brain activity.  In their studies, these researchers have found that introverts and extroverts use different parts of their brain in processing information, as evidenced by differences in increased brain flow.  Asking individuals (some were introverts and others were extroverts) to "think freely," the scientists used positron emission tomography (PET) to measure cerebral brain flow, which is an indicator of brain activity.  After comparing the results that they yielded from the two groups, Johnson and Wiebe found that "introverts showed increased blood flow in the frontal lobes, the anterior hypothalamus, and other structures associated with recalling events, making plans, and problem-solving," whereas "extroverts displayed more activity in the posterior hypothalamus and posterior insula, regions involved in interpreting sensory data."  By looking at these differences, the two researchers deduced that this difference in brain activity confirms that introverts have more of an inward focus and extroverts have more of an outward focus, both as a result of how their brains function.  Whereas the brain function of introverts complements attention to internal thoughts, that of extroverts is driven by sights and sounds, in lieu of sensory stimulation.  This study was published in an article by Michelle Gallagher in Psychology Today, and even though the article is admittedly a bit dated (first published on July 1, 1999) and somewhat biased (the author assumes that introverts have to be quiet thinkers and extroverts have to be partygoers), the research itself still reveals that the differences in behavior between introverts and extroverts are due to differences in brain processing.  Not only do these differences in brain processing and function determine how an individual will behave, but they also thereby lead to the individual's classification as an introvert or an extrovert.  Fortunately, individuals can still fight this disposition (even though the author of the article mistakenly asserts one's behaviors and classification are set in stone).     (Gallagher)

("Psychic Energy and MBTI")

Another example in which introverts and extroverts generally differ in brain activity, other than the regions in which they show increased processing, are their dopamine/neurotransmitter systems.  Among other neurotransmitters, dopamine is responsible for giving the individual the experience of pleasure and happiness.  When an individual's brain registers a certain experience as satisfying, it releases dopamine, which essentially communicates to the individual as a whole that they are/should be pleased and happy.  Placing individuals under a brain scanner, researchers have found that, when taking gambles, extroverts show "a stronger response in two crucial brain regions: the amygdala and the nucleus accumbens."  While the nucleus accumbens affects how individuals learn and "is generally known for motivating individuals to search for rewards," the amygdala "is responsible for processing emotional stimuli."  In essence, because extroverts exhibit a stronger response to dopamine in their amygdala and nucleus accumbens, their "brain tends to push them towards seeking out novelty, taking risks, and enjoying unfamiliar or surprising situations," giving "that rush of excitement when they try something highly stimulating that might overwhelm an introvert."  This stronger response in the dopamine systems of extroverts versus those of introverts is likely due to the fact that, as previously explained, these two groups process information differently.  The pathway for processing information for extroverts is shorter than that of introverts.  This pathway for extroverts "runs through an area where taste, touch, and visual and auditory sensory processing take place.  For introverts, on the other hand, this pathway is more long and complicated, running through "areas of the brain associated with remembering, planning, and solving problems."  Because the processing pathways for extroverts are shorter, they receive more instant gratitude, and thus they also crave/need this instant gratitude more than introverts.  Introverts can be overwhelmed by some situations that extroverts flourish in, and their processing pathway leads them to evaluate the quality of an experience, before receiving gratitude.  Thus, whereas extroverts can and will act more on the spur of the moment, introverts usually need more time to assess a situation.  At times, introverts will remove themselves from a situation that extroverts will actually throw themselves into.     (Cooper)

Like dopamine, acetylcholine is a neurotransmitter.  This visual representation's mention of acetylcholine may be a mistake, but regardless, it illustrates that extroverts have shorter information and gratitude processing pathways than introverts, which may thereby encourage their behavioral differences.  (Cooper)

The behavioral differences between introverts and extroverts are greatly due to the differences in how their brains function and information is processed.  From areas of increased brain activity to length and route of dopamine pathways, introverts and extroverts are different because their brains handle information differently.  At the same time, individuals are not forever fixed in the manner in which they process information.  Often times, brain processing and function has only been found to correlate with, not necessarily cause, an individual's classification as an introvert or an extrovert.  Therefore, to some degree, these differences in brain function and processing may actually be due to the individual's actions (the reverse of the proposed hypothesis), or both items may be similarly affected by a variety of confounding factors.  By and large however, the differences in behavior between introverts and extroverts may be explained by the way(s) in which their brain function and process information.



As a reminder, I could use as many responses as possible to my survey concerning your opinion(s)/public opinion(s) on the behavioral differences between introverts and extroverts, so if you have not participated yet, please consider responding soon.  In addition, I would appreciate it if you would encourage others to participate in the survey as well.  You can reach my survey by clinking on the link, and I thank you in advance for your support/response.

https://www.surveymonkey.com/s/62238YL

If you would like to read the articles that I pulled my information from, please use the following links:

http://www.fastcompany.com/3016031/leadership-now/are-you-an-introvert-or-an-extrovert-and-what-it-means-for-your-career

https://www.psychologytoday.com/articles/199907/the-difference-between-introverts-and-extroverts

Works Cited:

Cooper, Belle Beth.  "Are You An Introvert Or An Extrovert? What It Means For Your Career."  Leadership Now.  Mansueto Ventures, LLC, 21 Aug. 2013.  Web.  27 Feb. 2015.

Gallagher, Michelle.  "The Difference Between Introverts and Extroverts."  Psychology Today.  Sussex Publishers, LLC, 11 Jun. 2014.  Web.  27 Feb. 2015.

Jarrett, Christian.  "What Neuro-Revolution? The Public Find Brain Science Irrelevant and Anxiety-Provoking."  Center for Genetics and Society.  CGS, 5 Nov. 2014.  Web.  27 Feb. 2015.

"Positron Emission Tomography Facilities Through Imperial Consultants."  Imperial Consultants.  IC Consultants, Ltd, n.d.  Web.  27 Feb. 2015.

"Psychic Energy and MBTI."  One Over Epsilon.  WordPress.com, 14 May 2014.  Web.  27 Feb. 2015.

Can Introverts and Extroverts Coexist?

 

Extroverts and introverts are wired differently, but we still have to live in the same world.  Do we coexist,/How well do we coexist, and how can we establish the most successful friendships?  (Ravenscraft)

(Ravenscraft)

This blog post should be quick, right?  Obviously introverts and extroverts can peacefully coexist...it is obvious, right?  In theory, yes, it is quite evident that both introverts and extroverts can successfully coexist in this massive world.  Society has never fallen apart because of a misunderstanding between the two groups, and human life has never ceased to exist.  As explained in previous posts, if the two groups bridge over the misconceptions and misunderstandings that they have about one another, they should be able to tolerate, if not respect, the other group's strengths and weaknesses.  Moreover, the world is large enough that individuals from one group can simply ignore those from the other group if they grow too intolerable.  By and large, American society, although made up of many diverse groups, exists as one cohesive unit, even though there are separations such as the introvert-extrovert divide.

Obviously, introverts and extroverts can coexist in peace (well, at least it seems obvious), but can they coexist in friendship, and how?  ("Green Peace Signs")

However, I am asking whether introverts and extroverts can cooperate on the small scale.  I am asking whether they coexist on the small scale (personal relationships), and if so, what the methods are for which they can enjoy each other's company.  An individual may attempt to quickly answer the first question, stating that they are an extrovert, yet they have many introvert-type friends.  I myself believe that I am a slight introvert (shocking!), but I do have extrovert-type friends.  On the other hand, how close do we really feel with these "friends" who are of the opposite type than us.  By and large, do not introverts typically feel closer to introverts and extroverts typically feel closer to extroverts?  Generally, yes, but there are rare coincidences in which an extrovert will feel as close with their introvert-type friends as they do with their fellow extrovert-type friends, and versa.  What is the cause behind this phenomenon?  The key to successful comradery and friendship between individuals from the two groups is communication.

The first step to respecting the differences between introverts and extroverts is understanding these differences.  (Schwerty)

According to one online source (and most of my blog posts), the difference between introverts and extroverts is the way that they recharge.  Being an introvert does not necessitate a hate for all people, and being an extrovert does not necessitate a love for all people, but introverts do need to recharge by having alone time while extroverts have to recharge by staying in the company of others.  At times, introverts can become overwhelmed if they have not had their time to recharge and are constantly thrusted into social situations, and extroverts can become drained if they are denied the company of others and left alone.  However, this does not mean that introverts cannot (theoretically) handle large, intense social situations.  Before and after entering such situations, however, introverts need time to recharge.  Likewise, extroverts can exist in solitude, but they still need to recharge as well.

Can you guess whether this individual (drawn by an artistic master) is an introvert or an extrovert?  ("Introvert/Extrovert")

Thus, awkward situations can ensue at times when two friends, one an introvert and the other an extrovert, have a misunderstanding about the quality of their friendship.  For example, this pair of friends may have spent a grueling week at the office, and as a result, they are looking forward to different outcomes for their weekend.  The introvert wants nothing more than to go home and relax, whereas the extrovert cannot wait to go out and party, or at least go to some sporting event.  Being that they are friends, the extrovert may ask the introvert to go out with him.  By and large, there seems to be an unwritten understanding between members of the same group, in that introverts understand other introverts and their need to recharge in solitude, and they are therefore not extremely offended when one turns down their offer to go out, as extroverts understand other extroverts and their tendency to go out in society often for recharging, and they are therefore not extremely offended if they are not invited to every outing that this individual goes on.  However, because introverts and extroverts undeniably do function differently, they often do not see such behaviors/situations in the same manner, and they usually fear the worst.  Moreover, because individuals often feel unable to communicate their needs so that members of the other group will understand them, a lack of communication occurs, which leads to further misunderstanding.  The introvert, upon receiving the offer, may politely deny it, informing the extrovert that they need time to spend at home.  The extrovert, accepts the introvert's explanation/excuse, but they then think back on the fact that they have invited the introvert to go out with them three weekends in a row, and their offer was only accepted once.  Thus, the extrovert, even though they consider the introvert a friend, may believe that the feeling is not mutual, and may further decide whether or not they should invite the introvert out anymore.  Whatever the decision, the introvert may also recognize, over time, that the extrovert may only invite them out once or twice a month, yet they are still always going out every weekend, albeit with different people.  The introvert may mistake this for the idea that the extrovert and them may not be as close of friends anymore, although the extrovert's reason is really not to cause offense (either because they simply go out all the time and thought nothing of it or because they had sensed that the introvert's recurrent excuses were a signal for the end of their close friendship), and, thus, when the introvert does decide to go out, they may go out with other individuals as well, but never with their extrovert friend.  Because the two individuals struggle to communicate their needs and feelings related to such situation(s), they may have possibly ruined a once close friendship.

Communication is the key to successful friendships between introverts and extroverts (in other words, an individual must speak their mind).  ("Communication")

How are such situations avoided?  How is it that there are still close friendships between introverts and extroverts in existence?  Communication is the key to success.  In order to understand each other, two friends that belong to the separate groups must speak their minds, telling the other about their needs/feelings, and the listener must be willing to receive, understand, and accept their friend's feelings as legitimate fact and not shaky excuses.  This does not mean that introverts can never go out, but they still need their time alone, which extroverts need to accept.  Likewise, because they will not be going out all of the time but their extrovert friends still need company, introverts need to accept that their extrovert friends can have other friends and go out without them.  Moreover, extroverts should accommodate for their introvert-type friends, giving them prior notice of when they can go out together so that the introvert(s) can make plans revolving around this and suggesting options that may not always include just the packed club.  Again, introverts can also accommodate for their extrovert-type friends, making sacrifices to go to events where there may be many people and recognizing that they will not die on the spot from too much stimulation.  Basically, in order for an introvert and an extrovert to coexist in a close, peaceful, successful friendship, both individuals must exercise understanding, communication, and planning.

(Jackson)

It may be a cliche phrase to use, but it has always been said that opposites attract.  Obviously, if an individual is an introvert, they can still have introvert-type friends, and if they are an extrovert, they can still have extrovert-type friends.  However, it is also not taboo to have extrovert-type friends when an individual is an introvert and to have introvert-type friends when an individual is an extrovert.  On the other hand, such friendships can be littered with awkward situations and misunderstandings when communication and accommodation are not used.  If both groups can understand each other as a whole through bypassing the misconceptions that society teaches them about one another, individuals should also be able to avoid such misunderstandings that they have with friends from the different "camp."  Introverts and extroverts may be/can be/are behaviorally different, but by understanding such behavioral differences and recognizing one's similarities with the other individual, successful friendships/relationships can still be made.

(Ravenscraft)

Believe it or not, I have decided to extend the deadline for collecting the results of my survey for yet another week.  Currently, I already have a whopping three responses to my survey, but I feel as if I could probably use at least a couple more responses (like, maybe two hundred more) in order for my results to be accurate.  Thus, I ask those who have not participated in my survey yet (everybody) to please take a couple minutes to submit their opinions and then encourage others to participate as well.  In order to reach my survey, just click on the link below, and it should (magically) take you to (the wonderful land of Narnia and) my survey concerning the behavioral differences between introverts and extroverts.  I thank you in advance.

https://www.surveymonkey.com/s/62238YL

Works Cited

"Communication."  Study Hungary.  McDaniel College, n.d.  Web.  20 Feb. 2015.

"Green Peace Signs."  ClipArtBest.com.  ClipArt Best, n.d.  Web.  20 Feb. 2015.

"Introvert/Extrovert."  The Five Basic Temperaments.  The Five Basic Temperaments, n.d.  Web.  20 Feb. 2015.

Jackson, Michael L.  "Do Opposites Attract? The Extrovert/Introvert Dichotomy."  GoodTherapy.org.  GoodTherapy.org, 19 Feb. 2014.  Web.  20 Feb. 2015.

Ravenscraft, Eric.  "How Introverts and Extroverts Can Peacefully Coexist."  Lifehacker.  Kinja, 2 Jul. 2013.  Web.  20 Feb. 2015.

Schwerty, Scott.  "Presentation Skills for Introverts and Extroverts."  The Blog.  Ethos3, 5 Nov. 2014.  Web.  20 Feb. 2015.

Revisiting: Genotype-Environment Interaction

How do the environments that you subsist in interact with your genes to influence behavior (environments of any kind, from social to ecological, count)?  ("Environment and Natural Resources")

(Plomin, DeFries, Knopik, and Neiderhiser)

As described in last week's post, I am revisiting the concepts of genotype-environment correlation and genotype-environment interaction for two weeks as I attempt to qualify/fix the definitions and explanations that I had used in prior posts.  Last week, I covered the subject of genotype-environment correlation, and this week, I plan to cover the subject of genotype-environment interaction.  This concept relates to and explains the behavioral differences between introverts and extroverts in that it reveals the tendencies of individuals to act based upon their genotypes, depending on their expression in the current situation.  The central idea behind the concept of genotype-environment interaction is that individuals are genetically predisposed to certain conditions (say, introversion or extroversion), and upon assimilation into the environment, depending on the situation, these predispositions may tend to come out.  Unlike genotype-environment correlation, the point of focus in genotype-environment interaction is not the fact that genotype plays a role in determining one's environment (although this is still significant), but it is instead the individual's reaction to such environment and the tendencies and predispositions that bear fruit without actually manipulating the situation.

 

("Behavioral Genetics")

To start from the beginning, according to Behavioral Genetics, Sixth Edition, by Plomin, DeFries, Knopik, and Neiderhiser, genotype-environment interaction is defined as "genetic sensitivity or susceptibility to environments."  In theory, both cognition (thinking) and genetics (inherent instinct) determine behavioral traits, thereby suggesting that one's behavioral traits, or at least the predispositions to express such traits, are inherited from the individual's parents.  These traits, which can also be expressed as genetic sensitivity or susceptibility, play a role in determining one's behavior in certain environments.  The focus of genotype-environment interaction is the individual's response(s) to a variety of environments (taking into account both environment type and individual's reaction/response), as affected by genetic predisposition.  This concept, in integrating both genetics and environment into explaining one's behavior(s), thereby suggests that behavioral traits, such as social introversion or social extroversion, are products of both nature (biology) and nurture (environment).  One of the basic theories of genotype-environment interaction, as articulated in Behavioral Genetics, is that, "when considering the variance of a phenotype, genes can affect the phenotype independent of environmental effects, and environments can affect the phenotype independent of genetic effects.  In addition, genes and environments can interact to affect the phenotype beyond the independent prediction of genes and environment."

Adopted, separated identical twins are often used in genotype-environment interaction research studies.  ("Genetic research-twin studies, family studies and adoption studies")

For example, research has shown that adopted children whose birth parents had criminal convictions have an increased risk of criminal behavior, thereby suggesting genetic influence (in terms of aggression and obedience).  In addition, research has shown that adopted children whose adoptive parents had criminal convictions also have an increased risk of criminal behavior, thereby suggesting environmental influence.  However, adopted children have been shown to be at an increased risk of criminal behavior when both their adoptive and biological parents have had criminal convictions in the past, thereby indicating genotype-environment interaction.  Not only do genetics affect the individual's behavior, but so does environment.  When individuals exhibit a genetic predisposition to a behavior, any corresponding environment amplifies this tendency/behavior.  Similar studies have indicated links between genotype-environment interaction and depression or alcoholism.  Further studies have been conducted concerning genotype-environment interaction making use of separated, adopted identical twins.  Research has revealed that when a pair of identical twins are separated by adoption, the two individuals are subject to exhibit similar yet slightly different behaviors due to their environment, with the individual whose environment encourages this behavior more to exhibit it more often (for example, two twins may be separated at birth by adoption; one goes to a family where the parents have exhibited criminal behavior(s), while the other one goes to a law-abiding family; both can still become criminals, but the one subjected to the environment with criminal adoptive parents is more likely to exhibit criminal behavior; the child living with adoptive parents who have exhibited criminal behavior may grow up to hold up banks and assault pedestrians, whereas the child living with the law-abiding adopted parents may grow to steal candy and gum from gas stations and commit tax fraud).  Further research into such subject has also shown that the likelihood of either member of this pair of twins exhibiting the behavior is greater if their biological parents exhibited such behavior, as compared to the likelihood of either member of a separate pair of twins exhibiting the behavior if their biological parents did not exhibit such behavior.  The point/findings/result of twin adoption studies are that biology and genetics can create a predisposition to a behavior, which is then fulfilled/amplified if the environment is related to/accommodates the situation for such behavior.

Therefore, in essence, if an individual is dissatisfied with being an introvert or an extrovert, they have both their parents and their environment to blame.  Individuals inherit predispositions to behavioral traits, such as being an introvert or an extrovert, from their parents, and depending on their environment, which may encourage or discourage such behavior/identification, the behavior can be amplified.  Because individuals have genetic predisposition to behave instinctively, depending on the situation, their behavioral traits are influenced by both nature and nurture.  Thus, this concept is termed as "genotype-environment interaction" in that an individual's genotype and environment factor in, or interact, to determine the individual's normal behavior, such as acting as an introvert (speaking little, avoiding eye contact, keeping head down, etc.) or as an extrovert (speaking loudly and quickly, pursuing social contact, keeping head up, etc.), in such situation.  However, because genotype and environment affect and influence, but do not determine, behavior, their actions in certain situation are ultimately up to cognitive reasoning and processing (although this can also be affected by nature and nurture).  Therefore, the individual truly may only have themselves to blame for when they complain about being introverted and extroverted; nature and nurture are simply biased third parties that influence behavior, whereas cognition is the ultimate factor.

("Gene-Environment Interaction")

As a side note, yet another individual has participated in my survey comparing behavioral differences between introverts and extroverts as well as public opinion of the two groups!  Thus, I now have three responses to my survey!  If you can find some time to participate in this "overwhelming movement," please feel free to click on the link posted below and take my survey!  In all honesty though, I really would appreciate, if you are reading this blog post, that you take a few moments to participate in my survey and then encourage others that you know (family, friends, pets, inanimate objects, etc.) to do so as well.  I thank you in advance.

https://www.surveymonkey.com/s/62238YL

Works Cited:

"Behavioral Genetics."  Macmillan Education.  Macmillan Education, 2013.  Web.  13 Feb. 2015.

"Environment and Natural Resources."  University of Wisconsin-Extension.  University of Wisconsin System, n.d.  Web.  13 Feb. 2015.

"Gene-Environment Interaction."  National Institute of Environmental Health Sciences.  Department of Health and Human Services, n.d.  Web.  13 Feb. 2015.

"Genetic research-twin studies, family studies and adoption."  ISE IB Psychology 2012.  Tangient LLC, n.d.  Web.  13 Feb. 2015.

Plomin, Robert, John C. DeFries, Valerie S. Knopik, and Jenae M. Neiderhiser.  Behavioral Genetics.  6th ed.  New York: Worth Publishers, 2013.  Print.  Pages 118-127.

Revisiting: Genotype-Environment Correlation

("Gene-Environment Interaction"; This is the name of the article that I got this picture from, but my post itself focuses on genotype-environment correlation.)

Previously, I wrote a post describing the concepts of genotype-environment correlation and genotype-environment interaction as well as their application(s) to the behavioral differences between introverts and extroverts.  However, after speaking with my mentor, I find that I may have glazed over some of the more important points to these concepts and/or misinterpreted their application(s).  Thus, I plan to revisit the concept of genotype-environment correlation in this post, and I will revisit the concept of genotype-environment interaction in next week's post.  In revisiting these concepts, I believe that I can provide more comprehensive and accurate explanations, which will not only allow my audience to better understand these topics and their application(s) to the behavioral differences between introverts and extroverts, but it will also provide me the chance to ensure that I have a firm grasp of these concepts as well.  For my post today, I will be using the textbook Behavioral Genetics, Sixth Edition, by Robert Plomin, John C. DeFries, Valerie S. Knopik, and Jenae M. Neiderhiser as my main source of information.

The driving idea behind the concept of genotype-environment correlation(s) is that "we create our experiences in part for genetic reasons."  In other words, the environments that individuals are subjected to and/or create, whether willingly or inadvertently, are partially products of the individual's genotype/genetic traits.  As previously discussed, the definition of a genotype is "the genetic constitution of an individual organism."  Thus, even by the name of the concept itself, one can reason that the genotype-environment correlation is a concept in which the environment that one lives in is a product of their behavioral tendencies, which are coded for in their genetic makeups.  In some instances, what may seem to be an environmental influence may simply be a reflection of genetic influence/identity.  Individuals may assume that being subjected to a certain environment affects a certain trait, but it may be the trait itself, coded for genetically, that leads to the individual being subjected to the environment.  Due to its nature, "genotype-environment correlation has been described as genetic control of exposure to the environment."

("Heredity")

A crucial point to note about genotype-environment correlation is the individual does not necessarily have to subject themselves to said environments willingly in order to display a correlation between their genetic tendencies and choice of environment.  Environment amplifies the behavioral differences between individuals in that the environments that they subsist in are a reflection of their genetic tendencies, and the fact that the individual is genetically suited for such environment further illustrates variance in behavior.  In order to organize the different ideas surrounding the central of concept of genotype-environment correlation, researches and scientists have designed three types of genotype-environment correlations for different situation to fall into:

1. Passive Type
"The passive type occurs when children passively inherit from their parents family environments that are correlated with their genetic propensities."  In simpler terms, because many of our traits are genetic, and because we inherit our genes from our parents, we share many of the same traits with our parents, whether we like it or not.  Although individuals may look physically different from their parents, their actions and behaviors will always exhibit some influence from their parents' genes.  As a child/adolescent, one's parents subject themselves to an environment that suits the parents' needs as well as the kid's/kids'.  In other words, parents actively create an environment of their liking at home that suits their genetic tendencies and normal behaviors.  Whereas the parent is actively creating this environment, however, the children are simply forced into the environment.  At the same time, because this environment is based on their parents' genetic tendencies, behaviors, and interests, and because individuals inherit many of their genetic tendencies, behaviors, and interests from their parents, they passively subsist in this environment as well.  Although this environment is likely not created with their "genetic propensities" in mind, this environment still accurately meets the individuals genetic tendencies.  As a result, one's demonstration of behavior and genetic propensities is amplified, as they are comfortable in an environment that suits their behavioral needs (at least for the most part).  In the previous post, I mentioned the textbook's example of a musically gifted child.  The musically gifted child has it in their genes to express musical talent, and they inherited this predisposition to musical talent from their parents.  Their parents, who thereby would also have to be musically gifted, would provide their children an environment conducive to the development of musical ability, as they themselves would feel best comfortable in such environment.  Because this environment suits the parents' behaviors, genetic tendencies, and interests, it will also suit the child's genes and predispositions, as they inherited their genes from their parents.  An individual could have musical ability, but if they are not subjected to a home environment that is conducive to music-making, they will not be given the opportunity to display this ability.  However, because in this situation the home environment is conducive to the development of music, the child's behavior(s) and predisposition to musical talent will stand out.  Likewise, the probability is that if you are an introvert/extrovert, your parents will likely demonstrate the same leanings as you.  Given that many/most traits are heritable, it is safe to assume that introversion/extroversion, the results of biological functions, are heritable by effect.  In passive type genotype-environment correlation, the child does not create the environment, but the parent does.  Obviously, introvert-type parents would conduct environments conducive to introverts (through rules, mannerisms, traditions, etc.) whereas extrovert-type parents would conduct environments conducive to extroverts.  By effect, as introvert-type children will likely be born to introvert-type parents and extrovert-type children will likely be born to extrovert-type parents, each child would usually be subjected to the environment conducive to their behaviors.  The child does not necessarily change in respect to introversion/extroversion because of their environment, but because of their environment and its accommodation to their genes, they feel more freely to express their innate behaviors, which are amplified.  Thus, even as children, introverts and extroverts will demonstrate their respective behaviors, coded for in their genes, because of the conductivity of their environment, created by their genomically equal parents.

2. Evocative Type
"The evocative, or reactive, type occurs when individuals on the basis of their genetic propensities, evoke reactions from other people on the basis of their genetic propensities."  Once again, in this situation, the individual does not intentionally create the environment for themselves.  Rather, based on the behaviors and predispositions that they express, individuals evoke a response from others, who react and adapt to create an environment "fitting" for that individual.  In other words, the individual does not actively seek out an environment conducive to their interests, talents, genes, etc., but they instead let it come to them.  In most instances, adults will recognize the genetic tendencies that a child or peer express and recommend them for some program/opportunity/activity that they believe will fit their makeup, or children and/or adults may simply recognize these expressed genetic tendencies, and, recognizing that these traits are similar to their own, they make friends with the individual.  In essence, the individual does not intentionally create the environment.  Other individuals, who recognize the individual's talents and behaviors, instead react and create the environment; in other words, the individual's genes, by effect, create the environment.  At this point, once again, the situation that the individual is placed in is again representative of their genetic tendencies and behaviors, without even looking into how the individual acts in such environment.  By studying how the individual subsists in such environment, however, their genetic tendencies, talents, and behaviors are amplified, putting more emphasis on the correlation exhibited.  The textbook continues the example of a musically gifted child by mentioning that they may be "picked out at school and given special opportunities," such as entrance into music festivals that they did not even apply to.  This is an example of evocative type genotype-environment correlation in that the child does not intentionally expose themselves to such environment(s), but others instead adapt in recognition of the individual's talents.  Likewise, introverts and extroverts do not always have to actively seek out environments conducive to their needs.  Fellow introverts/extroverts may recognize their behavioral similarities with the individual and select them as a friend, or superiors (teachers, bosses, etc.) can recognize these behavioral tendencies and adapt the environment (class, workplace, etc.) so that it its most conducive to their needs.  These behavioral differences are thus amplified in that the individuals are placed in situations where the traits are most blatant and exposed, not to mention in that it is a testament based upon which environment they were placed into in the first place.

3. Active Type
"The active type occurs when individuals select, modify, construct, or reconstruct experiences that are correlated with their genetic propensities."  This type of genotype-environment correlation is possibly the easiest to recognize and understand in that the individual actively seeks and subsists in an environment conducive to their needs, genetic tendencies, and behaviors.  Although others may not have a hand in creating this environment, as they do in passive type and evocative type genotype-environment interaction, the individual can still actively create the environment on their own.  In doing so, the environment that they choose is once again (almost blatantly) representative of their genetic tendencies and behaviors, and their performance and actions in such environment serve as testament to and amplification of these traits.  For example, the textbook mentions that "even if no one does anything about their musical talent, gifted children might seek out their own musical environments by selecting musical friends or otherwise creating musical experiences."  The action of seeking out these environments and friends reveals the character and nature of the individual, and in subsisting in an environment conducive to their genes, the individual portrays their genetic predisposition to musical talent and interest.  The behavioral differences between introverts and extroverts can also be exhibited in this manner, in that their search for friends and a conducive environment reveals their behavioral instincts and innate tendencies, and that their actions in this environment, which is conducive to their traits, are amplified so as to demonstrate the variance of behavior created by the wide variance in environment.

"Passive genotype-environment correlation requires interactions between genetically related individuals.  The evocative type can be induced by anyone who reacts to individuals on the basis of their genetic propensities.  The active type can involve anybody or anything in the environment."  In being able to recognize the different types of genotype-environment correlation, one can identify how an individual's environment was created, as well as what this type means in respects to the individual's genetic tendencies and behaviors (is the environment simply a creation by the parents? is it a product of the reaction by others based on the behaviors of the individual? is it a deliberate choice that the individual seeks to subsist in? how do the individuals, like introverts and extroverts, seem to vary in behavior based on their environment and the tendencies and interests that are amplified?).  Too often, when analyzing the causes of a behavior, individuals immediately cite environment.  However, as environment is a by-product of genotype and behavior, it is at times a device for amplification rather than for cause and effect.  It reveals the differences in choice(s) and action(s) of individuals, which can be directly applied to the contrast in behaviors between introverts and extroverts.

(Rutter)

Next week, as mentioned before, I will be exploring genotype-environment interaction, the partner concept to genotype-environment correlation.  Also, I would greatly appreciate if, before then, you could please participate in my survey regarding the behavioral differences between introverts and extroverts, as well as encourage your friends, peers, and colleagues to participate in it as well.  The link to the survey is below if you would be willing to participate.  Thank you.

https://www.surveymonkey.com/s/62238YL

Works Cited:

"Gene-Environment Interaction."  National Institute of Environmental Health Sciences.  U.S. Department of Health and Human Services, 28 Aug. 2014.  Web.  6 Feb. 2015.
"Heredity."  Certificate Biology.  Certificate Biology, n.d.  Web.  6 Feb. 2015.
Plomin, Robert, John C. DeFries, Valerie S. Knopik, and Jenae M. Neiderhiser.  Behavioral Genetics.  6th ed.  New York: Worth Publishers, 2013.  Print.  Pages 107-118.
Rutter, Michael.  "Why the Different Forms of Gene-Environment Interplay Matter."  SlideShare.  LinkedIn Corporation, 26 Jul. 2010.  Web.  6 Feb. 2015.