Survival of the Sickest Part 3

What did you think about the reading?

From my perspective, “Of Microbes and Men” as well as “Jump into the Gene Pool” were one of the most informative and most fun chapters to read so far. All the topics discussed from parasitic worms to jumping genes truly captivated my attention. I continue to appreciate Dr. Moalem’s evolutionary perspective on all these chapters, for it allows me to view topics in a way I never did. I am looking forward to reading the next chapters.

What did you learn?

Chapter 5 begins by talking about parasitic worms, more specifically the Guinea worm. This worm is eaten by water fleas that fill sources of water in remote tropical areas. These worms stay alive inside humans when we drink this water because our digestive system does not destroy the larvae. The worm then secretes acid to burn the host’s skin which then leads them to use cold water as a relief. Once the larva senses the water, it emits its eggs into the water, restarting this cycle of infection. The chapter continues on by talking about another example of host manipulation in nature, the parasitic wasp known as Hymenoepimecis argyraphaga. This wasp paralyzes a spider who then becomes host of the wasp’s eggs. The larva eventually manipulate the host into spinning a cocoon for them and then the larva kill the spider and develop in the cocoon until it becomes a wasp. Dr. Moalem continues by giving the example of the lancet liver fluke and how it goes from sheep to sheep by going through a snail, and eventually manipulating an ant to be eaten by a sheep. Also, he talks about the parasitic hairworm in the south of France and how it manipulates a grasshopper into drowning itself. He continues by talking about T. gondii and its manipulative process on mice or rats to basically become cat food. What was even more surprising was that T. gondii actually affects humans with a severely compromised immune system. I also found interesting that some events that we think of as symptoms are actually host manipulation of bacteria or virus.

Chapter 6 was all about DNA. Learning that less than 3% of your DNA contains directions for building cells was really surprising. The other 97% isn’t active in building. At first, scientists labeled this 97% “junk DNA” because they thought that it did not code for cellular reproduction, they actually thought it was parasitic. However, after new research began, we learned that this “non-coding DNA” plays a significant role in evolution. I also learned that 1/3 of our DNA comes from viruses. Barbara McClintock discovered whole sequences of DNA moving from one place to another and affecting genes nearby. Today, these are called “jumping genes”. A study demonstrated how much of a difference a jumping gene could make when used right. A jumping gene was able to allow a fruit fly to resist starvation and withstand high temperature and its life expectancy was 35% longer than usual. McClintock also observed that the jumps were not random and she even believed that they would go towards places where mutations were beneficial. Jumping genes are still a topic that is the center of much research. It was also observed that jumping genes are very active in early stages of brain development.

Do you have any questions?

Because these chapters contained much information, I have a variety of questions. Are there other instances that host manipulating parasites affect only humans? What would happen to the parasites if the hosts undergo a mutation that counters the attempt of parasites to manipulate them? Why does T. gondii only have guaranteed survival in cats? What other examples exist, if any, that a jumping gene affected an organism in such a beneficial way as the fruit fly? How have jumping genes affected humans today?

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One thought on “Survival of the Sickest Part 3

  1. These chapters were also my favorite and the Guinea worm was a truly remarkable example of how human have learned to adapt to the problems they face. Your question about “What would happen to the parasites if the hosts undergo a mutation that counters the attempt of parasites to manipulate them?” is kind of what I was thinking. Would the parasite just leave the host or will it too mutate and adapt to again be able to manipulate the host again.

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