Saturday, April 3, 2010

Natural Selection <--> Immunity

A story of natural selection at work: Jerry Coyne in his book tells a similar story of natural selection acting on the coat color of mice. (pg 116)

Therefore, it can be inferred that natural selection is not solely a mechanism, but rather a process, as Coyne asserts. What are some other examples of selection acting in nature that refutes the misheld notion that “everything happens by chance”? (pg 118) Furthermore, because adaptations increase the fitness of the individual, and thus the chance of survival increases for the individual to pass down “good” genes, Coyne describes an example relating human-induced artificial selection on bacteria; in the end the bacteria was able to “grow on a previously unusable food” source (pg 129). Connecting the idea of selection to immunity: how does the bacteria’s “evolution” relate to antibiotic resistant bacteria? In general, what is the evolution of resistance in your opinion and what are some solutions to counter it? (Would u consider evolution in this sense a curse or a blessing?) How does the immune system of humans specifically cope with such a predicament? (relate to Ch 43 in Campbell if necessary)

1 comment:

  1. First, I would like to establish, in the simplest terms possible, what natural selection really entails. The simplest possible way of describing natural selection is the "non-random survival of random traits" (Coyne 119). That is, new traits show up through mutations and other such changes purely based on chance, but what dictates their survival is whether those traits actually help them survive and reproduce at greater rates than before. That is, previously stated in the prompt, why bacteria evolve to become resistant to antibiotics. Randomly, a bacteria will experience a mutation that causes resistance to antibiotics. However, the trait, even though it arose randomly, will continue to express itself because it makes the bacteria more fit to the environment, and thus the gene is passed on non-randomly. All traits are selected like this, even ones that may seem a bit more esoteric.

    One may say that peacock feathers, with their well-known ornamentation, are an exception to this rule. Huge feathers are often misinterpreted as being like a red flag to predators, saying “eat me!!!” and one might think that this trait survived only by chance. However, not so! This trait is actually selected because “male peacocks display their iridescent feathers for prospective female mates” (Discovery) and give them a greater chance at attracting a mate for reproduction, which goes under the umbrella of “survival and reproduction” that I introduced earlier. But, how is this important to bacterial evolution? It shows that even the most complex, strangest traits are selected for a reason, yet arise randomly. The peacocks developed their ornate feathers over hundreds of thousands of years of generations in evolution, but what is so scary about bacteria is that generations are so short and so plentiful that selection of traits can arise quite quickly.

    That is how we connect natural selection and immunity… because humans create and have been using antibiotics “for decades in human and animal medicine…drug-resistant strains of bacteria are emerging” (CSIRO). Humans are actually creating an environment, with copious amounts of antibiotics, that challenges bacteria to survive and thus creates the potential for these random traits to be selected through non-random means. In this case, evolution would definitely be considered a curse, as switchover to new remedies for bacterial infections is slow and the continued antibiotic use breeds even more dangerous bacteria. However, alternatives exist, such as cytokine treatments. These treatments involve “proteins naturally produced by the body’s immune system following infection by bacteria or viruses” (CSIRO) being introduced into an organism in order to fight the infectious disease without using antibiotics. Cytokines are the natural thing that humans and other organisms use to naturally fight disease, so it makes sense that mass-producing them for widespread treatment is a smart idea. All in all, with the pace bacteria are evolving at to resist antibiotics, it is imperative to find a different way of fighting bacterial infection.

    Page 119 of the book