In footnote 155, Shenk notes Jean-Baptiste Lamarck's belief that future generations are under, "the influence of the predominant use of permanent disuse of any organ," by the prior generation (344). Lamarck supported his theory with the example of the giraffe's elongated neck, which supposedly came to be because it is, "obliged to browse on the leaves of trees and to make constant efforts to reach them." (345) Shenk also mentions in footnote 156 Charles Darwin's popular theory of evolution, citing Douglas J. Futuyma's statement that evolution is the theory, "that populations evolve by changes in gene frequency brought about by random genetic drift, gene flow, and especially natural selection," and that the development of organisms is not at all related to free will. What aspects of the theory of evolution make it more plausible than Lamarckism? Also, how has history supported either Darwinism or Lamarckism (cite specific examples)? Are there examples that could go either way?
(Adithi Rao, adithi.a.rao@gmail.com)
(Adithi Rao, adithi.a.rao@gmail.com)
Among the aspects that make evolution seem more plausible than Lamarck's theory is the understanding that "we cannot change our genes" (Shenk 157). The genes inherited from parent to child in the form of DNA have identical copies throughout an individual's body in each cell throughout an individual's lifetime. The fact that the common understanding is that these inheritable codes are not changed by an individual's actions have led to a mockery of Lamarckism in the face of Darwin's evolution. Historical support of Darwinism is widespread. A specific example of the evolution of a species is John Endler's study of predator's effects on male guppies' coloring (Campbell 460-461). The bright coloring of male guppies attracts both female guppy mates and potential predators. Endler found that in populations that suffered a greater intensity of predation, through the process of natural selection, the new generations of male guppies possessed more drab coloring as it was a selective advantage for survival in their environment and allowed them to live to reproduce more drab colored guppies while brightly colored guppies did not survive as successfully. Other examples of Darwin's theory of evolution are evident in fossil records demonstrating the differences and developments that led to modern-day species or the extinction of those that were not equipped to survive their changing environment.
ReplyDeleteWith our modern understanding of epigenetics or the idea that an individual's actions can "affect [...] gene expression and that of future generation's", Lamarck's theory is no longer as absurd (160). Epigenetics is distinctly different from Lamarck's theory, particularly in the sense that it can coexist with evolution; still, examples of human behavior in a single generation having a lasting inherited effect on offspring such as cigarette smoking and nutritional deficiencies is both remarkable and compelling in the face of Darwinian evolution of heritable traits with the child as a genetic blank slate rather than some developed traits and their effects carrying across the generations.
Kate White (kw2020@gmail.com)
Darwinism is more plausible than Lamarckism because it has been consistently proven by the history of many species of animals. Darwinism is more focused on the ideas that animals have no choice in the matter of evolving, because evolution occurs by natural selection and the “survival of the fittest.” Lamarck’s idea depicts evolution as the result of animals adapting to a certain situation because they have to, which is not true. Just like his idea of the giraffe having a large neck due to the need to reach the tops of trees, evolution simply doesn’t work that way. Logically, Darwinism makes much more sense. 3.8 billion years ago was the start of the appearance of simple cells such as prokaryotes. The appearance of the first anatomically modern humans appeared 200,000 years ago. If Lamarckism was true, evolution would have occurred much faster. Evolution is described to be "genetic variation [driven by] natural selection as individuals with advantageous traits are more likely to reproduce successfully, passing these traits to the next generation, which is called adaptive evolution" (http://www.biology-online.org). Support of Darwinism can been seen in the transition of life to the sea such as dophins and whales. These are fossils found by many scientists that show from the terrestrial ancestor of the whale Pakicetus to the recent wale ancestor Balaena(Campbell, 462). Support for Darwinism can also be found in anatomica and molecular homologies, such as the similarities in mammalian forelimbs from the human arm to a cat’s leg forelimb to a bat’s wing to a whale’s fin. They have have the same basic skeletal elements (Campbell, 463).
ReplyDeleteLike Kate said, in recent years, support for the basic idea of Lamarackism that environment has an impact on genetics has arisen. That support has come in the form of epigenetics, so Lamarckism doesn’t seem as crazy as before. Epigenomes are the packaging that surrounds the DNA. These epigenomes can be changed by the environment, and is, therefore, “an important mechanism for gene-environment interaction” (Shenk, 159). What this demonstrates is that the environment has a perceptible impact on the traits that we express. So, the evolutionary process became to be viewed as a more “interactive” one (Shenk, 161). However, a unique trait of epigenetics that wasn’t discovered until 1999 about epigenomes is that, epigenomes can actually be inherited from one generation to the next. Epigenetic inheritance do not directly involve the nucleotide sequence. However, your epigenetics can be subject to change at any time. The proteins in your epigenomes can turn traits and genes on and off in reply to stimuli from the environment. Thus, epigenetic inheritance is heavily on the environment, which supports Shenk’s idea of GxE, that the environment playing a huge role in the traits we express.
Differing epigenomes do lead to different gene expressions, even in genetically identical organisms. It was observed by scientists that two genetically identical toadflax flowers had different appearances due to differences in environment (Shenk, 157-158). This same phenomenon has been seen in genetically identical twins. These twins with the same genetic sequence have incidences where one twin acquires a genetically based disease such as schizophrenia, bipolar disorder, and cancer while the other does not (http://www.nytimes.com/2005/07/05/health/05gene.html). Epigenomes make it possible for the genome to essentially be responsive to the environment. Thus, in part, epigenomes does support Lamarack. However, the actually process of evolution is much more related to Darwinism opposed to Lamarackism.
(Yanfei Gao, feifeiyg@yahoo.com)