Monday, March 8, 2010
Evolution Today
Many ID proponents refute the evidence for evolution by saying that its not readily observable. While evolution is the gradual divergence of a species from its previous form due to adaptive advantages from genetic variation among individuals, Jerry Coyne mentions an example of the production of lactase (an enzyme used to digest milk) in humans beyond infancy is due to the rise of "pastoral" farmers. Another example of modern evolution mentioned by Jerry Coyne--is the increased presence of allele CCR5-Δ32 in humans, which provides significantly increased resistance to AIDS virus. (pg. 217-9) Why is this information important? How can small adaptations today turn into a bigger evolutionary change in the future (give examples of how this could happen)? Where is evolution still occurring today--not just in humans? (Hint: Why did we discuss the need for vaccinations and seasonal flu shots in biology class?)
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Modern evolution is apparent in the form of microevolution. This refers to the change in gene frequency within a given population. For example, House sparrows were introduced to North America in the 1800s. Now, sparrow populations in the north have larger bodies to withstand colder temperatures while sparrows in the south still have smaller bodies. Examples of microevolution can even be seen within one lifetime. For example, whiteflies microevolved resistance to pesticides. Modern evolution is apparent in the form of microevolution. This refers to the change in gene frequency within a given population. House sparrows were introduced to North America in the 1800s. Now, sparrow populations in the north have larger bodies to withstand colder temperatures. Examples of microevolution can even be seen within one lifetime. For example, whiteflies microevolved resistance to pesiticides. Macroevolution differs from microevolution due to speciation. Speciation involves extensive genetic variation within a species resulting in an inability for two organisms to reproduce. I.D proponents argue that since macroevolution is difficult to observe, it must not exist. However, if genetic variation occurs within species, it does not seem impossible to acquire variation that inhibits species reproduction ("Understanding Evolution"). Grasping evolution today is essential for various technological implications. For instance, vaccines and pesticides must be altered frequently to adapt to microevolving organisms. Evolution today is even more important because it tells us the direction the species of the world are headed.
ReplyDeleteI agree with Dani (very well thought out)...
ReplyDeleteIn the world today, humans are what control many instances of modern evolution, which is classified as microevolution. Modern technology has major influences on the environment, which causes species to adapt to stay alive. Also, our breakthroughs in science and medicine have caused us to not only live longer, but fight natural selection of our own kind. Along with this fact, the uses of gasoline and our everyday energy expenditures fluctuate many different habitats and cause modern species to become increasingly adapted to a dynamically changing environments. For example, in a previous JAE I completed, urban house sparrows were better at problem solving than rural house sparrows because they are better suited to an environment, which is different from day to day. Like Dani said, what we see today is microevolution, but over millions of years, these small changes will eventually lead to the point where reproduction cannot occur among the evolved species and the modern-day species (speciation). In this day and age, artificial selection by humans proves to be very powerful. Darwin described this as "the selective breeding of domesticated plants and animals to encourage the occurrence of desirable traits" (Campbell et al., 2008). We can grow genetically modified fruits and vegetables (ProQuest) and produce vaccines to combat infectious diseases like the flu. This is a good topic for us to discuss in class because each year, although people may not realize, their seasonal flu vaccine has changed in order to keep up with the presently evolving influenza virus. According to the CDC, a "seasonal influenza vaccine [should] be administered to all age groups as soon as it becomes available. Antibody to seasonal inactivated influenza vaccine declines in the months following vaccination." This means that once you receive a flu shot, it will eventually wear off in the future simply due to the idea of microevolution: "the occurrence of small-scale changes in allele frequencies in a population, over a few generations, also known as change below the species level" (Wikipedia). This is a prime example of natural selection because it exemplifies the survival of the "most fit" RNA viruses of the family Orthomyxoviridae (Wikipedia). The most fit are able to survive the medicinal vaccine and continue to infect the body. Our medical research must keep evolving to continue to maintain this disease from becoming a world-wide epidemic, which it caused in the past before the great age of technology.
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ReplyDeleteAs an add-on to Max's previous comment, it is important to realize that "microevolution" occurs not only in viruses but in bacteria as well. This is demonstrated in MRSA, properly known as Methicillin-resistant Staphylococcus aureus, which is resistant to almost every antibiotic developed save Vancomycin, according to a video shown earlier in the year when discussing Prokaryote organisms. The "microevolution" that occurred over time was driven by the inadvertent selection of traits expedient to the Staph's survival in harsh conditions, which in this case is during exposure to antibiotics! In short, the use of antibiotics over time killed off the weak bacteria and left the "fitter" bacteria surviving. Needless to say, large-scale antibiotic use actually inadvertently caused humans to evolve such bacteria into a more dangerous form. Ironic, to say the least.
ReplyDeleteThe phenomenon of humans selecting traits in bacteria is nothing new. According to a UC Berkely article about the so-called “superbugs,” all the way back in the early 1940s “penicillin-resistant strains of S. aureus were unknown – but by the 1950s, they were common in hospitals.” This just goes to show the speed at which this type of microevolution occurs, as a prominent trait like antibiotic resistance could not develop in any other type of organism in the span of time given. Ten years would not even be a single generation in most species, whereas bacteria such as Staph experience millions upon millions of generations in that sequence of time. That, coupled with the high probability of random mutations, means that microevolution can occur. But, what exactly is microevolution?
In the simplest possible definition, microevolution “refers to changes in the frequency within a population or a species of its alleles (alternative genes) and their effects on the form, or phenotype, of organisms that make up that population or species” according to a TalkOrigins article about the subject. As such, it is not the speciation per sé that occurs in macroevolution due to many traits separating organisms to the point where they can’t reproduce, but the gradual change of a species within itself to become fitter to the environment, as stated on page 133 of the book. Going back to MRSA, then, one can say that microevolution has occurred as the trait towards antibiotic resistance is in higher prevalence, yet there is nothing preventing normal Staph from “reproducing” (as in sharing DNA through transduction because bacteria really don’t reproduce sexually) with MRSA successfully. In conclusion, the evolution that is strictly visible today is microevolution in the case of MRSA, while the real deal, macroevolution, is Darwin’s true implication and takes much longer.
Sources:
http://evolution.berkeley.edu/evolibrary/news/080401_mrsa
http://www.talkorigins.org/faqs/macroevolution.html
Page 133 of “Why Evolution is True”