Saturday, April 11, 2009
Any Means Necessary
Carrol discusses on page 186 how natural selection does not create the most efficient solution possible but rather "works with whatever materials are available." In the example of the ice fish, the loss of red blood cells was seen as an advantage in the survival of the species in their surroundings, but there was also the disadvantage of having the red blood cell gene fossilized, making the process almost irreversible. The reasoning given by Carroll is that mutations are "all a matter of the immediate benefits outweighing the immediate costs, if only by a slim margin." Give two examples of a species (at least one that was discussed in the book) that has evolved in a manner that may not be the most efficient. Discuss the advantages and disadvantages of the mutation and an alternate mutation that would have been more beneficial and explain why this was unable to occur. What caused the true mutation to occur even if there was a downfall? Discuss how if those mutations had been beneficial only by a slim margin at that time, how they are now affecting the species.
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In natural selection, mutations that provide an immediate benefit are preserved through the generations. Because of this, traits chosen through natural selection do not display any foresight as to what may be the best adaptation for the future; instead, it only works to adapt to present conditions. In the cases of the blood of the ice fish, the fossilization of the red blood cell gene allowed them to better adapt to arctic conditions, but it may prove debilitating if they must migrate to warmer temperatures in the future.
ReplyDeleteHumans have also adapted certain traits that are not very efficient. Caroll specifically mentions the rise of sickle-cell anemia. The condition is widely considered a disease. Those with sickle-cell anemia have red blood cells that are deformed, so they die out much quicker than normal red blood cells. This causes many medical complications and severely shortens overall lifespan. Despite all these negative effects, the trait for sickle-cell anemia is a selective advantage in certain areas where there is a high risk of catching malaria. Malaria is an infectious disease often transmitted by mosquito bites. The deformed red blood cells of sickle-cell anemia are resistant against malaria. And while sickle-cell anemia can cause difficulties and shorten lifespan, the affects of malaria are far more detrimental. As a result, as a selective advantage against the disease malaria, natural selection chose for a less severe disease, sickle-cell anemia.
Another interesting, seemingly inefficient adapation is the movement of small cats. In most four-legged animals, the movement of the body as the animal walks is energy-efficient. Logically, natural selection has chosen for body movement that preserves energy in order to reduce the amount of muscular work required. This is not the case with cats. Instead, the cat's movement operates at high energy cost and low efficiency. This is counterintuitive because it means that cats are stressed by the same number of strides than other animals, such as dogs. However, this disadvantage does allow for more stealth. The inefficient gait of the cat gives it much more stability and makes less sound. This allows the cat to sneak up on its unsuspecting prey, though if the prey is alerted, the cat's are not as suitable for the chase.
http://www.umm.edu/blood/sickle.htm
http://www.sciencedaily.com/releases/2008/12/081203184533.htm
http://www.plosone.org/article/info:doi/10.1371/journal.pone.0003808
The cheetah, Acinonyx jubatus, is an example of a species that evolved in a less efficient way. The cheetah is the land’s fastest animal without the ability to climb. It is the fastest land animal, reaching speeds between 70 and 75 mph in short bursts covering distances up to 1,500 ft, and has the ability to accelerate from 0 to 68 mph in three seconds. This ability to sprint gives cheetahs a selective advantage when hunting its prey. However, the cheetah’s ability to sprint is not very efficient. Although it can reach high speeds, its body cannot stand long distance running. The cheetah does have adaptations that enable the cheetah to run very fast including large nostrils for increased oxygen intake, enlarged heart, and enlarged lungs.During a typical chase its respiratory rate increases from 60 to 150 breaths per minute. While running, in addition to having good traction due to its semi-retractable claws, the cheetah uses its tail as a rudder-like means of steering to allow it to make sharp turns, necessary to outflank prey who often make such turns to escape. Despite these adaptations, the cheetah is a vulnerable species. Out of all the big cats, it is the least able to adapt to new environments. Also, despite their speed, cheetahs are largely outranked by other large predators in most of their range. Because they have evolved for short bursts of extreme speed at the expense of both power and the ability to climb trees, they cannot defend themselves against most of Africa’s other predator species. They usually avoid fighting and will surrender a kill immediately to even a single hyena, rather than risk injury. Because cheetahs rely on their speed to obtain their meals, any injury that slows them down could essentially be life threatening.The cheetah has an average hunting success rate of around 50%. Running at speeds up to 70 mph puts a great deal of strain on the cheetah's body. When sprinting, the cheetah's body temperature becomes so high that it would be deadly to continue. Therefore, the cheetah’s adaptation to extreme speed is not a very efficient adaptation. It would have been more beneficial if the cheetahs underwent an adaptation that gave it great speed, but also adaptations that allowed cheetahs to have endurance. If they could manage to run pretty quickly for a long period of time, they would have a great selective advantage over other predators in its habitat. This was unable to occur due to the complications of energy expenses of running in great speed for a long period of time. It would require so much energy that it is nearly impossible to achieve. The mutation that allowed the cheetahs to gain great speed was selected for due to the success rate of hunting. In the past there were more prey for the cheetahs to hunt for, so it was a selective advantage to have greater speed, without the need to run long distances to catch a prey. However, with the cheetah’s hunting range decreasing and preys becoming less available today, it is harder for the cheetahs to hunt and catch its prey. It was a selective advantage in the past, and it is becoming more of a disadvantage due to less prey, resulting in the cheetah’s need to run for long distances in order to find and catch its prey.
ReplyDeletehttp://en.wikipedia.org/wiki/Cheetah
http://www.defenders.org/wildlife_and_habitat/wildlife/cheetah.php
(continued from above)
ReplyDeleteHumans, as Nikhil stated above, have evolved in other ways that are not the most efficient. The fossilization of the MYH16 gene provides the protein for muscles, particularly the very prominent temporalis muscle that extends over most of the area of each side of the temporal region of the skull (Carroll 134). Given the large temporalis muscle is involved in movements of the large jaws in apes involved in chewing, humans’ temporalis region muscles are much reduced compared to other primates. The loss of the MYH16 protein, a myosin that forms part of the large fibers within muscles that generate their force, gives humans a disadvantage, since they have weaker muscles for chewing. The loss of muscles in the jaw somewhat limits the humans’ diet. It would have been better for the survival of humans if their jaws were stronger, allowing them to eat harder food. This mutation that resulted in the fossilization of the MYH16 gene may have resulted due to the effect of another mutation that provided a selective advantage. It may have been a by-product. However, since humans obviously survive better than primates due to their domination in the world, this mutation does not affect humans that much. Humans still survive well even though they have weaker jaw muscles. This fossilization of the MYH16 gene also shows that the making of the fittest is not necessarily a progressive or additive process. The selective advantage of a certain gene caused the degeneration of the MYH16, becoming an evolutionary change but not a selective advantage.