Evidence:
In chapter four, Shenk reveals a more specific example of the environments influence on a person's physical structure using evidence from Michael Rennie. The human body is made and influenced by the environment and natural endowment (genes). This is how two identical twins can "sculpt their bodies by different training regimes” (266) creating two different body types.
If the environment was the same and people had similar lifestyles could the body structure be the same? How does this idea relate to the theme of 'relationship between structure and function' between the environment and the shape the body?
If the environment was the same and people had similar lifestyles could the body structure be the same? How does this idea relate to the theme of 'relationship between structure and function' between the environment and the shape the body?
Christine Park (go2christine@hotmail.com)
If the environment was the same and people had similar lifestyles, then the body structure would still not be the same. Although the GxE model suggests that environmental influence on genes in the outcome of an individual, “human body size and composition are as much a matter of environment as of natural endowment, with each having about 50% influence” (Shenk 266). Although environmental factors do play a large role in determining an individual, it is impossible for two individuals’ body structures to be completely identical. Michael Rennie describes how two identical twins sculpted their bodies differently due to different training methods; however similar training methods will not result in identical body types. For example, Shenk describes the Jim twins, Jim Lewis and Jim Springer who “shared a womb for nine months…and were raised in working-class towns seventy miles apart…and [had] some of the same habits” (Shenk 83). The alarming similarities were attributed to the similarities in the environments they were raised in; however, they still were not identical. While their genes and environments were similar, they still had different life experiences, which shaped who they were. The influence of many genes can influence behavior, and “many scientists think that…behavior is shaped by a large number of genes that individually have small effects” (Campbell 1132). These single-locus variations in genes can influence the behavior of individuals of the same species, and a variation at a “single locus can cause dramatic differences in behavior” (Campbell 1132). Individuals in different habitats can have significantly different behavior, even if they possess some of the same genes. For example, two species of prairie voles that are closely related demonstrate different behavior in mating and parental care. The male meadow voles do not get attached to their mate or their pups, while the male prairie vole has one mate and invests much care into the raising of the pups (Campbell 1132).
ReplyDeleteRia Singh (riasingsing@gmail.com)
Just like in human twins, even if the genes are similar, and the environments are similar, traits (like body structure) are not guaranteed to be the same. Even in clones, the personalities and physical traits are not guaranteed to be the same. DNA can be cloned using bacterial plasmids to make recombinant DNA. First, the plasmids should be isolate from the DNA intended to copy. Then, both should be cut with the same restriction enzymes, and then some will join by base pairing, and the pairs will be sealed with DNA ligase. Then, the place the bacteria on agar with ampicillin and Xgal, and if the cells had taken up the recombinant plasmid, then they would appear on the plate and multiply, creating many bacterial clones (Campbell 399). Cloning does result in the exact replicated DNA, like the DNA of Dolly the sheep (http://www.ornl.gov/sci/techresources/Human_Genome/elsi/cloning.shtml). Dolly was not an identical clone although her chromosomal DNA was the same (http://www.ornl.gov/sci/techresources/Human_Genome/elsi/cloning.shtml). For example, even carbon copy clones, like the cats Rainbow and CC who shared 100% of the same genes, will not be 100% identical because “the degree to which the GxE dynamic guarantees enormous differences between originals and their copies” (Shenk 73). The cats, Rainbow and CC, have different physical traits and personality traits, which proves that even if the genes are 100% identical, the environment plays a significant role in determining the outcome of the individual because “environment interferes in the pathway from genotype to phenotype” (Campbell 1142). Even if the environment was, in fact, the same, and the lifestyles were similar, two people could not have the same body type because of subtle differences due to varies experiences. Furthermore, the DNA nucleotide sequence provides instructions for the outcome of the individual, “many factors-including the environment of the fertilized egg and the animal’s diet, social interactions, and surroundings-modify how these instructions are carried out” (Campbell 1129). The specific influence of genetics and environment on behavior has been explored by twin studies, and these twin studies have revealed that “the degree of susceptibility governed by genetic differences between individuals…is almost always greater than 20% and less than 80%” (Campbell 1130). The relationship between structure and function determine body type because of the function of the body. For example, if running is a daily part of someone’s life, then his or her heart muscle will be more efficient in transporting oxygen and other nutrients to the tissues because of strenuous exercise having high energy demands. The idea that “form fits function” can be seen in every structural level of life (Campbell 7). Even if two people are in the same environment with the same demands, their body types will not be exactly the same because there does remain genetic difference.
ReplyDeleteRia Singh (riasingsing@gmail.com)