In chapter 6 of Making of the Fittest, the author, Sean Carroll goes in depth about evolution and why it repeats itself. Chance, selection and time are the main pattern of evolution. Mutations occur by chance because it is random, and selection is reliable for keeping or getting rid of mutations. These mutations will continue to occur. However, if the mutation is not beneficial for the species, then it will get rid of it. If it is useful for other species, it will be selected and kept.
Carroll begins the chapter discussing about howler monkeys and how they developed trichromatic vision independently of Old World Monkeys. Both Howler monkeys and the old-world monkeys carry trichromatic vision in their DNA. However, the gene in howler monkeys occurred 20 to 25 million years after the traits were evolved in their ancestors. Due to similar conditions in different parts of the world, traits are gained and lost. The author states that howler monkeys are a widespread phenomenon in nature called convergent evolution. Convergent evolution takes places when species evolve similar traits as independent inventions from different lines of descent. They originally did not have such traits. An example that Carroll gives, “The flippers of penguins, seals, and dolphins, for example, all serve a similar purpose in swimming, but each group of animals evolved from different ancestors that did not have flippers”. Convergent evolution is significant because when species are put into similar conditions, they come up with similar solutions in adapting with the conditions.
Next, Carroll discusses about the Arctic and Antarctic fish species evolving “antifreeze” independently. We know these fish species developed antifreeze independently because they are distant on the family tree and are from different orders. Also, the time of water temperature lowering are different, “ the freezing of the North Atlantic and North Pacific oceans occurred much more recently, about 2.5 million years ago, indicating that the driving force for evolution of antifreeze was separate from that in the Southern Ocean, which dropped to freezing temperature about 10 to 14 million years ago”. Lastly, there is no similarity to the original digestive enzyme DNA that the antifreeze gene originally came from. The two sorts of antifreezes are made by up of two completely different processes. In the section about “Chance, Necessity, and the (Re)Making of the Fittest”, the author explainshow approximately once in 750 years a herring gull will be born able to see UV light. Having the UV opsin mutation is 1 in 500 million offspring bases and mutation happens when there is a Thymine at the site instead of an Adenine, which gives violet vision. The possibilities are multiplied by 3 (Thymine, Guanine, or Cytosine) which gives 750,000,000 offspring. Then dividing 750 million by the 1 million offspring equals 750. This number shows the chance of having herring gull chick with the UV mutation is once every 750 years.
To sum up, evolution repeats itself because of chance, selection and time. Due toconvergence of similar adaptation, repeating of events occur. My opinion about the quality of the writing is that it is all over the place and gets the reader lost. It jumps from one example to another which gave me a hard time to follow along. The author seems to have a lot of examples about the topics which makes it convincing. Also, the genetic diagrams that are shown in the book make it more academically credible.
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