DNA has been proven to be hereditary, and epigenetic material is also passed on,
"which helps guide how the genes will be expressed. While genes
themselves do not change (by and large) from generation to generation,
the epigenetic material can change" (118). While genes can be
changed between generations, the environment seems to be a bit more
decided than previously thought because we tend to, "conform to
established cultural norms" (118). How do these insights change the old
nature/nurture paradigm? How large is the influence of past generations'
environments on a child? If all instructional material is not preset as
it is transferred from generation to generation, what influences the
changes, and how large are the affects? Can the environment of a parent
alter the epigenetic material they pass onto their children, and, if so,
how large of an influence does their environment have?
Jenna Sherman (jsherm013@aol.com)
The old nature versus nurture paradigm has dictated for many years that the way human behaviors behave and what they accomplish in life is either determined by nature, meaning the genes they have been given through “inheritance patterns determining genotypes in a manner often more complex than predicted by simple Mendelian genetics” (Campbell, 271), or by nurture, meaning the environment they have been raised in. This argument “is a very old and hotly contested debate” (Campbell, 275) which for many generations no one has been able to find a “correct solution” to. David Shenk in his book The Genius in All of Us proves that the old nature versus nurture paradigm is no longer relevant, because the real answer to what our accomplishments, characteristics, failures, etc are determined by, is more of a gray area, which Shenk calls the “GxE paradigm” whereby “we develop traits through the dynamic process of gene-environment interaction” (Shenk, 21). This complex process of gene-environment interaction is truly what creates the new epigenetic material that Shenk believes is passed on. In the past, it was believed that pure genetic material contained the instructions for building “your parent’s blue eyes or brown hair” (Shenk, 21). It was a continuous pattern that resulted from our “indoctrination of Mendelian genetics” (Shenk, 21). Every human being’s genetic material contained DNA and RNA, which would direct the production of proteins, creating new genetic combinations only through sexual reproduction or mutations, as dictated by the biological theme of continuity and change.
ReplyDeleteHowever, Shenk’s evidence proves this theory false. Rather, he states that epigenetic material is what can and does change, and is passed on. Epigenetic material accounts for the environment where “genes need to be activated – switched on or “expressed” – in order to initiate protein construction. The environment includes parenting, motivations, experiences, climate, etc are what cause genes to be turned on or off, thus the parent of a child’s environment certainly affects their child’s future. In fact, after 9/11 it was found that mothers who were pregnant with their children and were in or near the World Trade Center during the attack who had developed post-traumatic stress disorder had much lower levels of the hormone cortisol in their saliva. The next year, after their children were born, the children were tested, and it was found that their children also had lower levels of cortisol within their saliva. Interestingly enough, the children whose mothers had been in their third-trimester of pregnancy had lower levels than those who had been earlier in their pregnancies. Hence, the distress response of lowering cortisol levels and the development of PTSD was at least somewhat directly related to their mother’s stage of pregnancy. (http://www.guardian.co.uk/science/neurophilosophy/2011/sep/09/pregnant-911-survivors-transmitted-trauma) Essentially, the epigenetic material of the pregnant mothers had changed as a result of PTSD, and this was thus, inherited by their children. Because the epigenetic material had changed within the mother, the direction of the production of proteins which would contribute to the saliva of the infants had also changed and had been passed on. This is often the case with any disease or psychological problem within pregnant mothers and their children; stress responses affect epigenetic material, creating change within DNA and RNA.
Moreover, as Shenk states, our environment does have a tendency to “conform to established cultural norms” (Shenk, 118) which does explain why epigenetic material may remain seemingly “continuous” or “unchanged” throughout the generations. While many may believe that African-American athletes are simply more talented than their white counterparts because of supposed “hidden genetic advantages” (Shenk, 100), this “talent” is actually the result of conforming to certain social norms in geographical regions, creating a certain “set” environment contributing to success within the athletic realm. In Kenya, it became the established “cultural norm” to want to work to become a great runner. Young men who were good at raiding cattle were able to have what they “needed to pay for a bride” or even have “multiple wives.” (Shenk, 103) Those who had multiple wives had a reproductive advantage, because they were then more likely to themselves survive and reproduce, and also to have children that would survive and reproduce, the ultimate goal of biology. When in later generations, the reward for being a fast runner was prize money which would allow one to buy food for their families and themselves, and also survive and reproduce, the same principle applied. It became the established cultural norm to have a “fierce dedication to running” (Shenk, 103), thus turning on the expression of the special gene variant ACTN3, which although 82% of Europeans have, is not expressed because they do not have this “established cultural norm” to be dedicated to running. This epigenetic material is passed on over generations, making the Kenyans and other groups “better” at running. Because their parent generations had the environment which made them dedicated to running, this environment and the epigenetic material that comes with it is also passed onto their children.
ReplyDeleteIn conclusion, in a GxE paradigm, the environment certainly has a very large impact on the inherited genetic material of the child. Environment can include nurture of those around them, but also the environment and stresses of their parents. It can also include climate, parenting styles, needs to survive and reproduce, nutrition, etc, but genetics are certainly no longer black and white Mendelian genetics which make up “nature” of a human being.
(Michelle Kelrikh, mjkelrikh@gmail.com)
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ReplyDeleteThe old nature/nature paradigm revolved around the argument that the way a person turned out- talents, appearance, personality, etc.- was either a result of the way they were raised (nurture), or the genes they inherited (nature). However, Shenk presents a new way of viewing development: that of GxE, in which the environment is inextricably tied to genetic expression and in fact shapes how genes are expressed. He explains this with the concept of epigenetics, in which traits are not directly passed down as a result of genetic coding but instead “transmitted by mechanisms not directly involving the nucleotide sequence” (Campbell 358). In other words, environmental factors can interact with the “switchboard” that is our genome and influence how that genome is expressed; “human beings are distinct from one another not just because of our relatively few genetic differences, but also because every moment of our ongoing lives actively influences our own genetic expression” (Shenk 23). One gene can be activated or not, and then that can affect other genes’ activation, such as the examples we learned in class of pigmentation in a certain flower or the expression of agouti in rats. Therefore, even if two identical twins had the exact same genomes, if they were to grow up in different environments, different environmental factors would be at play to activate or deactivate certain genes, possibly resulting in two completely different people.
ReplyDeleteOn the flip side of that, Shenk acknowledges that many times, people with different genetic codes (as much variance as our genetic code allows for- “between any two humans, the amount of genetic variation… is about 0.1 percent”)- can turn out similarly (http://science.education.nih.gov/supplements/nih1/genetic/guide/genetic_variation1.htm) . For example, even though obviously not all Jamaicans are related, as a population they produce more world-class sprinters than any other country. Shenk then goes on to explain why, if Jamaicans don’t share the same genetic codes, and in fact compose a “quite heterogeneous genetic group, (Shenk 108) they as a whole succeed so fully in running. His assertion is that it is not purely genetics that give Jamaicans this “edge” in world competition but rather the environment in which they grow up and train. Shenk acknowledges that indeed there is some kind of genetic component to it: 98% of Jamaicans possess the gene variant ACTN3, which is said to produce proteins that aid in “forceful, speedy muscle contractions”, apparently contributing to sprinting success (Shenk 101). However, he then goes on to dismantle the easy belief that it is purely this genetic twist that gives Jamaicans their edge, because 80% of Americans also possess ACTN3 yet haven’t achieved the same level of success.
. Instead, he argues that the GxE interactions of the Jamaican culture of success have stimulated this success. So, perhaps the reason that more Jamaicans possess ACTN3 is a result of the intense training environment that promotes sprinting as the highest honor; “The reality of GxE assures that each person’s genes interact with his climate, altitude, culture, meals, language, customs, and spirituality-everything- to produce unique life trajectories. Genes play a critical role, but as dynamic instruments, not a fixed blueprint” (Shenk 107). Therefore, even though more Jamaicans possess ACTN3, this is not the key to success. Their true key to success is the E in GxE, which shapes them both on a genetic and a mental level. It not only plays a role in epigenetics, in activating certain genes to be expressed that may not be expressed in different environments- that would be the natural environment of Jamaica at work- but also in shaping the mindset of Jamaican athletes, who are encouraged from a young age to excel and realize that successful sprinting can be the key to prestige and economic success. For example, world’s fastest sprinter Usain Bolt said that spriting provided him a way of achieving his dreams of a big house and fame (http://proquest.umi.com/pqdweb?index=1&did=2615890861&SrchMode=2&sid=1&Fmt=3&VInst=PROD&VType=PQD&RQT=309&VName=PQD&TS=1334014500&clientId=15232). “In context of the developmental dynamic, psychology and motivation become vital” (Shenk 110). This connects to Shenk’s description of what “talent” truly is: not an innate skill set but rather the product of intense, laborious training. Jamaicans have the mindset and environment to promote the development of this amazing talent.
ReplyDeleteHowever, many times the environmental effects on epigenetics that are passed down through the generations look genetic since they appear so consistently and appear to have been passed down rather than shaped. This is misleading, however. Part of the apparent inherited talent is, indeed, the result of genetics since genes activated in previous generations are then passed on to the next generations in the same state, supporting Jean-Baptiste de Lamarck’s much vilified theory of inheritance of acquired characteristics, in which he argued that “an organism could pass modifications to its offspring” (Campbell 454). Most famously, he argued that giraffes passed longer and longer necks on to their offspring as a product of years of reaching for higher leaves. While this obviously is not correct, in Shenk’s partial defense of Lamarck, he states how “what an individual does in his/her life before having children can change the biological inheritance of those children and their descendants” (Shenk 161). As proof, he cites the various studies by respected scientists/institutions that demonstrated how choices made by one generation affected descendants: for example, “London geneticist Marcus Pembrey presented data… to show that nutritional deficiencies and cigarette smoking in one generation of humans had effects across several generations” (Shenk 160). From there, it is reasonable to assume that activation of certain genes, such as to cause increased ACTN3 prevalence in Jamaicans, can be passed on. If the Jamaicans who have ACTN3 are successful sprinters and thus achieve economic success, they can survive and reproduce and pass that ACTN3 on to their offspring; this natural selection winnows the gene pool down until the majority of Jamaicans have the ACTN3 that is so beneficial to survival in their society. But another part of “inheritance” is still due to the environment. However, this part is invisible and hard to distinguish from the genetic part. This is because environments tend not to shift drastically from generation to generation. Therefore, children’s epigenetic information is shaped much the same way as their parents’ was and they turn out similarly. As Michelle said, it is not truly due to any genetic superiority that Jamaicans are faster sprinters or Kenyans are better long-distance runners, no matter how much we’d like to tell ourselves that; not only did natural selection act to choose those who were fast enough to raid cattle and eat in Kenya, but in more modern times the culture in which they are raised and the fact that they exploit the ACTN3 gene to their advantage, while other cultures do not, contributes to success. In conclusion, “while the genome provides the possibilities, the environment determines which genes become activated”, and this is applicable to both a parent’s genetic legacy and to a child’s own genetic expression (http://www.school.eb.com/eb/article-288098?query=epigenetics&ct=). A parent’s environment can definitely shape their child’s and grandchild’s epigenetic expression, but an equally if not more important role is played by the environment itself reshaping the child’s genes; however, many times this reshaping is passed off as genetic because of the homogeneity of environments across generations.
ReplyDeleteVivian Wang (vivian.wang9895@gmail.com)