Shenk addresses the fact that twins that grew up in
different environments showed some extreme similarities; as Shenk states, “They
had each married and divorced a woman named Linda, and then each married a
woman named Betty. They each had an adopted brother named Larry and childhood
dog named Toy…They were each six feet tall and weighed about 180 pounds” (Shenk
75). If the two brothers grew up in different environments, how does the GxE model
explain such coincidences? Shenk later recognizes that while there were some
stark similarities, there were also myriad contrasts between the two such as
hair style, muscle development, and number of marriages (Shenk 83). What kind
of environmental factors could have caused these differences? Please provide
specific examples from the book.
Yiran Xu, yxu135@gmail.com
Behavior, anatomy, and physiology are all determined by interactions between genetic and environmental factors. Our DNA sequences provide the instructions for development, but many environmental factors determine how these instructions are carried out (Campbell 1129). Twin studies are often performed where researchers compare the behavior of identical twins raised apart with those raised in the same household (Campbell 1130). In the book, Shenk talks about the Jim twin study. They had so many similarities but at the same time very noticeable differences.
ReplyDeleteThe similarities can be attributed to the early shared GxE (Shenk 80). Not only do twins have the same exact genes, but they shared the same womb. Therefore, they had the same exact GxE interactions from conception until birth. Prenatal development of the twins exposed them to the same amount of stress, air quality, smoke inhalation, medications, and nutrients. Also, diseases can be spread to both babies before birth. The placenta can’t filter out extremely small viruses and bacteria, so once they enter, both babies are at risk (http://www.livestrong.com/article/233087-environmental-factors-affecting-fetus-development/). Even being separated after birth, they still had many similarities. This after birth coincidence is because of cultural circumstances (Shenk 81). Twins are the same age, same sex (for Jim twin study), same ethnicity, and most likely of same social and economic positions. Jay Joseph explains that these are the factors that increase resemblance of reared apart twins (Shenk 81). Coincidently, the also grew up within a few miles of each other which could have had an effect on the amount of similarities between them. They inherited many things, but they also have the potential to become very different people.
After the Jim twin study, there were observed differences such as hair style, muscle development, and number of marriages (Shenk 83). The obvious reason for the differences between the identical twins is the fact that they were living in different places with different people surrounding them. Even though they are twins, they were shaped by various habits, schedules, expectations, and surroundings (Shenk 119). Some of the factors that cause these differences are food, language, education, entertainment, and hobbies. The twins went to different schools, received different information, ate different things, got different amounts of sleep, and did different activities in their free time (http://www.thetech.org/genetics/ask.php?id=142). For example, one of the twins intensively trained for athletic advantages while the other twin was a long distance runner (Shenk 83). Their varying interests ultimately caused them to have different body structures. The one that trained was very buff while the runner was skinny; their bodies were required to adapt differently due to various genes being expressed. Another reason why the twins showed differences had to do with imprinting period when the babies form long lasting behavioral responses to particular individuals or objects (Campbell 1126). For a human, this critical period takes place around ages 3-5. This is the developmental stage when children begin to imitate what they see and have a large imagination (http://www.support4change.com/index.php?option=com_content&view=article&id=47&Itemid=108). A significant amount of learning takes place and since the twins were in different households, they were exposed to different scenarios that would have influenced this developmental stage.
(Katie Donnowitz kdonnowitz94@aol.com)