Lectures 1 2 Monday November 2 2009 Wednesday November 4 2009 An example of the relevance of evolution today The usual story is that Alexander Fleming accidentally discovered penicillin the story is that Fleming working in St Mary s hospital in London was working with a culture of Staphylococcus aureus a pathogenic bacterium on which he was doing some research when he noticed that it had become contaminated by a species of Penicillium He noted that the mold was inhibiting the bacterial growth He writes a paper on his finding in 1929 and the rest is history The actual story is a little bit different Fleming was searching for antibacterial agents as early as 1920 and was largely motivated by his World War I experience where he witnessed the deaths of many soldiers from septicemia blood poisoning In 1922 Fleming discovered lysozyme an enzyme that lyses bacteria In 1928 while researching staphylococci he benefited from chance and a well conditioned mind that was looking for agents that inhibited bacteria His lab evidently was not a very orderly one and cultures he worked on were often forgotten and hence contaminated eventually After returning from a month long vacation Fleming found many of his plates contaminated with a fungus He noticed a zone of inhibition around the fungus He thought he was on to something and eventually isolated an extract from the mold that by itself could inhibit the growth of bacteria He named the inhibitor Penicillin By 1943 drug companies were mass producing penicillin for the war effort Thousands of lives were saved by this miracle drug over the course of the war And of course the lives of perhaps millions of people were saved by penicillin and related drugs after the war For us it is difficult to imagine living in dread of dying of a bacterial infection of any kind But of course this was not always the case The last 50 years has been termed a golden age in medicine mostly because of the better treatment of bacterial pathogens 1943 marks the beginning of the antibiotic error 1947 however marks the beginning of the emergence of antibiotic resistant bacteria 1947 saw the first penicillin resistant pathogen Staphylococcus aureus By 1967 penicillin resistant pnemococci had surfaced and American military personnel in Southeast Asia were starting to bring home penicillin resistant gonorrhea The response by the medical community was a natural and reasonable one If penicillin doesn t work as effectively let s find another antibiotic The 1950 s saw chloramphenicol neomycin streptomycin tetracycline erythromycin and cephalosporins added to the list of antibiotics The 1960 s saw the addition of several new aminoglycosides but resistance to one aminoglycoside was often accompanied by resistance to other aminoglycosides An aminoglycoside acts by tightly binding to a structural component of the 30S ribosomal subunit to inhibit protein synthesis The 1970 s were bleak in terms of adding new antibiotics but the 1980 s saw the addition of an important new class of antibiotics called the fluoroquinolones of which Ciprofloxacin is probably the most familiar Fluoroquinolones inhibit gyrase in bacteria which is an enzyme that is necessary to separate DNA during cell division Over the past 60 years bacteria that are resistant to new drugs consistently appeared within a few years of the introduction of those drugs into clinical use By 1994 researchers had identified in patient samples bacteria that were simultaneous resistant to all currently available drugs Why First the emergence of antibiotic resistance is an example of evolution Biological evolution is the change over time of the traits of a species The trait that the bacteria differ in is their individual resistance to antibiotics Some bacteria are less susceptible than others to treatment by antibiotics The observation is this 60 years ago antibiotics like penicillin were widely in fact wildly successful at treating pathogenic bacteria Today those same drugs are less successful because the proportion of resistant bacteria out there has increased Evolution in this sense is a statement of fact not of theory A fact is something that can be observed We have observed unfortunately the evolution of antibiotic resistance in different bacterial species We have also observed evolution in other species over longer periods of time and have direct evidence in the forms of fossils that creatures in the past did not look like creatures alive today Second the evolution of traits such as antibiotic resistance is often caused by natural selection This is one of the big ideas that Charles Darwin had The idea is really simple 1 Individuals within a population are variable 2 The variations among individuals are at least in part passed from parents to offspring That is to say offspring resemble their parents 3 In every generation some individuals are more successful at surviving and reproducing 4 The survival and reproduction of individuals are not random and are tied to the variation among individuals The individuals with the most favored variations those who are better at surviving and reproducing are naturally selected Components of a successful theory of evolution 1 The fact of evolution We can observe that organisms change over time 2 The pattern of evolution How exactly do species change over time Is the change abrupt or do species change gradually 3 The mechanism process of evolution What causes species to change over time Also note that evolutionary biology is a historical science it attempts to explain events that occurred in the past It seems quite simple to explore the fact and pattern of evolution through direct observation using for example the fossil record However establishing a mechanism is not so easy In order to establish a mechanism that caused a historical event one must make an assumption The assumption is this Processes we see acting today also acted in the past This is not a particularly controversial assumption but it is key It underlies the sciences of geology astronomy and evolutionary biology among others The assumption of uniformity of processes over time is so important that the concept has a rather imposing name Uniformitarianism A couple of notes about the idea of uniformitarianism 1 The alternative to uniformatarianism is the idea that processes in action in the past were different than those today This is a variant of supernaturalism I think 2 Uniformitarianism does not mean that all changes have to be slow
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