Examples of Evolution
12/12/2010 § 1 Comment
Our last lecture was titled “Examples of Evolution” and talks of … examples of evolution. During this lecture, we (and the textbook) discussed different ways to see evolution on this world. The forms of evolution we discussed were Darwin’s finches and tuberculosis, a type of disease.
(Revisiting earlier ideas) Malthus once said that “People and organisms will always starve in the world. There are more animals than there is supply of food.” And although what Malthus stated was rather negative, (I do believe that he was just a negative person), it was also very true. So again, we revisit the idea that the individuals who survive the best in their current environment will be chosen to continue living, while those who don’t have the right characteristics will… be chosen to die. This is the survival of the fittest phenotype. This is also what we’ve studied as natural selection.
An example of natural selection (one of the biggest ideas we discussed during the 80-minute class) is tuberculosis. In the past few decades, tuberculosis has evolved. According to section 13.3 in the textbook, cures were found for tuberculosis during the 1950s: antibiotics were the way to keep people from getting diseases like tuberculosis. Yes, they were drugs and the type of drugs used to fight tuberculosis in the 1950s were specifically isoniazid and rifampin. It worked. For a while. By the 1980s though, stronger TB began to appear and these were immune to isoniazid and rifampin and pretty much all of the other drugs used previously to fight the bacteria in tuberculosis (called the mycobacterium tuberculosis bacterium – MTB).
What happened was one switch in the DNA. (This is where our knowledge of DNA structure and molecular genetics applies to this unit of evolution.) What used to be a Cytosine nucleotide in a link of DNA, on the specific gene called the rpoB, had mutated into a Guanine nucleotide. Before the mutation in the bacteria, rifampin could bind to the rpoB gene and stop the multiplication of bacteria, killing the MTB. After the cytosine base mutated into a guanine base however, the gene mutated in a way that the rifampin was not able to bind itself to it anymore and the bacteria was able to multiply.
(At least that’s what I understand from the book.)
That is one way that evolution exists, in tuberculosis bacteria. The disease itself is very threatening because it is an airborne sickness and in this part of the unit, we see why evolution matters. In this example, doctors can study and make sure they’re following the bacteria as it evolves so that they—the doctors—can also find cures and ways to keep up with the bacteria.
We also learned of Darwin’s finches—a type of bird. In the Galapagos Islands, finches were studied by Peter and Rosemary Grant and their characteristic were watched; their beaks, in particular, were monitored. The Grants noticed that during dry years, the beaks actually get bigger. (Actually, not get bigger but since the successful birds were the ones with big beaks, the percentage of big beaked birds increased above the small beaked birds.) Because the birds with bigger beaks were superior in surviving in their current environment, they were chosen, through natural selection, to continue their alleles for that year. However, when the years were wet, the smaller beaks outcompete the bigger beaks. This is because softer nuts (those easier to eat) were abundant during wet years and the birds didn’t need to waste energy growing a big beak (birds need ATP to make big beaks; it’s a tiring process for them).
Once again, this is an example of evolving to adapt to a particular environment.
Also, we saw an example in class that showed reproductive isolation which eventually leads to the formation of new species, or speciation. One example is birds again, like those on the Galapagos Islands. When one species (species A) moves to an island off the coast of the mainland, they start evolving to adapt to their new environment. Eventually, they’ve changed to a point where they’re similar to the original birds but quite different and are now species B. A selection of species B then migrates to another island nearby, one with different environmental conditions. Species B then becomes Species C, a new species. If species C tries to go back to the island species B resides on, the two species cannot interbreed anymore because they are different species now. Reproductive isolation has lead to speciation and we now have two new species of birds on the Galapagos Islands (B & C, the new species and A, the original species).
Test on Thursday. The essay question is How do things change? and since I’ve studied this unit last year, too, I’m confident with the knowledge I have now. I think, to answer the essay question, however, I will be choosing between the two sub-questions: a) How did eukaryotic cells originate? (from chapter 12) and b) How are new species formed? (from chapter 13). At the moment, I’m leaning towards b) How are new species formed? but I might decide against this tomorrow.