Sunday, March 17, 2013
Darwin and Lamarck
Big Idea 1 (the process of evolution drives the diversity and unity of life) is addressed on pages 134-135. Jean-Baptiste Lamarck and Charles Darwin are famous for their theories and work on evolution. What were their theories? How did Lamarck and Darwin prove their theories (explain their research)? What did Darwin prove that made Lamarck’s theory fail? Compare and contrast the theories of Lamarck and Darwin.
What book did Charles Darwin write? Explain the concept of ‘survival of the fittest.’ Explain the concept of ‘inherited acquired traits.’ Provide two examples of natural selection. How does natural selection drive diversity in the environment? What factors (genetic drift, bottleneck, etc.) play into diversifying populations?
Sigal Sasson (ssasson3@students.d125.org)
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The discovery of evolution by natural selection by Charles Darwin is one of the most fundamental aspects of biology. Big Idea 1 states, "the process of evolution drives the diversity and unity of life", and this is what Darwin was able to figure out. Darwin learned how populations adapt and evolve. According to his theory, there are naturally variations in a population due to random mutation and meiosis. Depending on many environmental factors called selective pressures, certain variations will be selected for and certain variations will be selected against. The individuals who have the variation that is selected for will be more likely to survive and reproduce; this concept is known as survival of the fittest. Over time, the population's gene pool will shift towards the variation that is selected for, which is adaptation, or microevolution. Over an immense amount of time and with biogeographical, pre-zygotic, and post-zygotic isolation, speciation can occur, which is called macroevolution. Before Darwin, many people followed Lamarck's ideas in which he proposed the idea of inherited acquired traits. Lamarck thought that traits that were acquired during an organism's lifetime would then be passed on to the organism's offspring. The classic example of this is the giraffe who stretches its neck. Lamarck would say that if the giraffe stretches its neck enough, its offspring will have a longer neck.
ReplyDeleteWhile Lamarck's theory was disproved by Darwin, scientists are now beginning to figure out that Lamarck's theory isn't completely wrong. Epigenetics is the new field of study that shows that certain environmental factors can make an imprint on one's DNA, which can be passed on to one's offspring. For example, if someone heavily smokes, a certain "tag" could be placed on his or her DNA, altering gene expression. DNA could be methylated at certain nucleotides, in which a CH3 group is added to it, and the DNA is not expressed. Histone acetylation can also occur in which a -COCH3 group is added to histone proteins, which causes the shape of the histone to change and DNA to be gripped less tightly, and the DNA is expressed (http://www.sciencemag.org/content/330/6004/611.short). Some of these epigenetic tags can stay in place and can be passed on to a person's offspring, rather than the epigenome being completely erased like earlier scientists used to think and which should be true if we completely reject Lamarck's theory of inherited acquired traits (http://learn.genetics.utah.edu/content/epigenetics/inheritance/). (Jeremy Bush jbush3@students.d125.org)
Jean-Baptiste Lamarck’s theory (or at least the one he wrote about) promoted the idea of the inheritance of acquired traits. This theory proposed that if an organism acquired a certain feature during its lifetime, then its offspring would obtain that feature as well. On the other hand, Charles Darwin is known for his idea of natural selection. This theory stated that the organisms that are better suited for their environment would be the ones who would survive and reproduce, thus passing on the beneficial trait to its offspring. Darwin ultimately proved that traits gained during an organism’s lifetime could not be passed down to future generations. One way he studied this was through pigeon breeding. http://evolution.berkeley.edu/evolibrary/article/history_14 The trait of a “neck ruffle” was selected for in the pigeons, and this became the predominating trait in the pigeon population. The breeder was similar a selective pressure in a natural environment. Lamarck’s and Darwin’s theories obviously rely on different mechanisms, but they both served to introduce the idea of evolution to the public in a convincing way. On page 135, Dr. Moalem even notes that at the time, Darwin even held the idea that inherited acquired traits were reality.
ReplyDeleteDarwin wrote the book the Origin of Species. This book championed the idea of survival of the fittest. This term means that organisms that fit best to their given environment will survive, and thus reproduce and pass on their fitting traits. Inherited acquired traits, on the other hand, was the idea that Lamarck has been credited with. This idea says that characteristics that organisms developed during their lifetime were passed onto their offspring, and that this was how evolution occurred.
One example of natural selection is the growth of antibiotic resistant bacteria. As we use more antibiotics, this kills off the weaker bacteria. Over time, we select for the bacteria that are resistant to antibiotics, and these are the bacteria that survive and reproduce. Another example is Darwin’s Galapagos Finches that he so closely studied. The 13 different species of finches all have different beaks. These evolved due to selective pressures in their particular environment, which was the food source. For instance, those with tougher beaks could eat large seeds, and those with long beaks could reach for insects. http://dsc.discovery.com/tv-shows/curiosity/topics/10-examples-natural-selection.htm This example also showcases how natural selection drives diversity. Different selective pressures allow different traits to flourish, and so many different species develop. Factors such as genetic drift and bottleneck can also diversify populations. These factors occur independently of selective pressures. Therefore, changes in the population can occur without certain selective pressures being present.
All of these ideas relate to Big Idea #1 (the process of evolution drives the diversity and unity of life). Darwin’s theory of evolution has shaped our understanding of how the diversity of the world came to be. Through the different selective pressures that power natural selection, biodiversity on earth can flourish.
Carolyn Fan (cfan3@students.d125.org)