In the argument section of Shenk's book, he discussed the incident of when two identical twins named Jim were separated at birth and then reunited; there were a number of striking similarities much more than just looking alike and talking alike such as "they had each married and divorced a woman named Linda... they had named their respective first children James Alan Lewis and James Allen Springer," and more (75). Shenk attributes their similarities to early shared GxE as well as shared cultural circumstances. For example, he states that both Jims have the same genes and shared the same womb for 9 months as well as growing up in similar "working class towns seventy miles apart" (83). Why, then, do siblings, who also have very similar genetics due to having the same parents and who have shared the same maternal womb as well as the same household and cultural environments, turn out so differently sometimes? Shouldn't they be very similar according to Shenk's argument? Bring in how inheritance works and the passing down of genes from parent to child. Also include the potential genetic differences in siblings due to the complexities of genetics. Does this disprove Shenk's idea or strengthen it?
(Yanfei Gao, feifeiyg@yahoo.com)
Twins have a 100% match of DNA with one another, this contrasts with the 99%-50% percent similarity of DNA that siblings have (http://www.eupedia.com/forum/showthread.php?25375-Unequal-genetic-similarity-between-one-s-mother-and-father). This is important to Shenk's argument because it shows that although siblings share the same womb, environment, and up bringing they do not have EXACTLY the same DNA. Shenk's GxE model states that "Genes. proteins, and environment signals constantly interact with one another...which forms traits" (Shenk 31).Because siblings do not have the exact same DNA, the environmental signals have different effects in each sibling. The traits of both siblings are interdependent of nature, yet the adaptions that are caused by this dependence are different due to the difference of DNA. In the case of Jim and Jim, because the have the exact same DNA and have almost identical environmental stimuli, the two twins had the same adaptions due to their dependence of nature.
ReplyDeleteThe fact that siblings who have lived in similar environments yet do not develop the same traits, supports the argument Shenk makes throughout his book. Shenk argues that "Gene activity is regulated by the intracellular environment... [which is] influenced by the environment of the individual" (Shenk 125). This shows that gene activity is dependent on the environment of the individual. For example, the amount of hormones released by endocrine organs or the amount of cytokines released from the immune system (Campbell 933) all are regulated by genes who are effected by the environment. Since the environment helps determine the genes that are expressed that means people with different DNA will have different reactions due to the environement because the DNA that is expressed in one person may not be expressed in another person. The biological theme of interdependence of nature shows the reason why siblings of a common environment do not share all the same traits. The reason for this is because although the siblings share the same environment, they do not share the same DNA; therefore, the expression of one type of gene in response to the environment may not occur in a sibling because he or she may not have the gene. This also relates to the GxE model because although siblings share a common environment, the environment has different effects on the genes of each siblings therefore creating different traits between the siblings. Jim and Jim developed almost identical traits because their DNA is exactly the same and their environment was very similar, therefore the same genes were expressed in each Jim causing similar traits between the twins.
The close parallelism between the traits of Jim and Jim, and the not so similar traits between siblings helps support Shenk's argument. These relationships relate to the GxE model and the biological theme of interdependence of nature, therefore, improving Shenk's argument
Joseph Hugener (jah1112@comcast.net)