Tuesday, March 30, 2010
Birdy
Coyne offers evidence for evolutions side against creationists that wing development would be a disadvantage rather than an advantage. He states that process would be simple, from the gliding step to the flapping of such wings to be able to fly. He offers proof in the form of the Archaeopteryx, which possesses large feathers and an opposable toe. Why would the development of feathers appear; Coyne says for insulation likely but wouldn't fur act as an equally efficient insulator and also not get in the way rather than large feathers, which would also create wind resistance to slow down the Archeopteryx from running? Also, it is necessary to have enough feathers in proportion to body weight to even glide an effective distance to escape from predators. Is it a possibility that such feather mass appeared simply through evolution for insulation? Offer evidence which provides for a stronger argument for evolution of birds and refute the claims made above.
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The first step to flying, as Coyne stated in the book, is gliding. The development of feathers would appear because furs do not allow the smooth gliding of air current through the wings. In organisms such as bats, they do not have furs directly on their wings. The shape of the wings allow the air current to smoothly flow through the wings, allowing gliding. Also the smooth gliding must have a big enough area to cause a faster current of air on the top of the wing than the bottom. This allows the bernoulli's principle of physics at work to allow the upward force that allows the lift. However,fur does not create such area. With millions of parts and large surface area, feathers act as a physics force that furs cannot create. Also like stated before, the feather mass can be seen as a proportion to amount of surface area it creates. Because larger surface area means more difference in pressure, the feather mass should be proportional to both insulation and the gliding motion. The affect of both of these forces would allow for the evolution of modern birds. If one cannot insulate its body, then it would die. Also if one cannot escape from its predators, it cannot survive.
ReplyDeletehttp://www.answersingenesis.org/tj/v17/i1/feathers.asp
Simply stated, evolution happens for a reason, and to better the surviving chance of the individual. For birds in particular, the evolution of modern day birds characterizes the birds as having double circulation and complex but efficient ventilation (breathing). Like mammals, birds require double circulation rather than the single circulation in bony fish, rays and sharks. Because mammals and birds descended from different tetrapod ancestors, and their four-chambered hearts evolved differently, this goes to show that wing development, like the development of the four-chambered heart, developed at the birds’ advantage. Furthermore, because birds need to fly at high altitudes, their unique gas exchange using parabronchi along with an efficient heart circulation and feathered wings, altogether work in favor of flight. (Campbell 902, 921)
ReplyDeleteIn addition to what liondrummer stated about bats, the same idea goes with squirrels. Because squirrels are able to glide with flaps of skin that extend along their sides, they do not need wings of feather or fur (Coyne 39). Furthermore, the structure specifically of the feathers belonging to the Archaeopteryx need to be examined: according to Coyne, the bird-like reptile had asymmetrical feathers that act like the modern wings of airplanes. This creates the “airfoil” shape necessary for aerodynamic flight. Also, feathers would not create wind resistance because of the thin shape that allows air to flow above and below it (refer to liondrummer’s explanation). Therefore, by using the mechanisms for flight described by liondrummer, the advantage for the Archaeopteryx would be to have feathers for insulation and flight rather than fur for just insulation.
In Coyne’s book pg 40, he also mentions that fossils found in China of feathered theropod dinosaurs having small filamentous structures covering the entire body (possibly early feathers) and one whose body was covered with long, thin feathers but were so small that flight could not have been possible gives evidence for another explanation of the use of feathers. The feathers give birds a skeletal adaptation for better balance and swift strike to capture prey whereas furs may provide a hindrance. Also, as with the peacock, the feathers may have been an impressive display to attract mates. The evolution of the alula later on, a tuft of specialized feathers attached to the thumb that alter airflow and allow control and maneuvering at slow flying speeds, became important for controlled takeoffs and landings. (Source: http://www.pbs.org/wgbh/evolution/library/03/4/l_034_01.html)
“At the southern extremity of the world lives the Emperor Penguin, better adapted to the cold than any other animal on earth. Short feathers made up of tiny filaments that trap the air in a continuous layer all around the body enable the adults and chicks to survive some of the coldest conditions on Earth, the Antarctic ice-cap in winter.” (Source: http://www.pbs.org/lifeofbirds/evolution/)
Therefore, perhaps feather mass appeared though evolution for insulation or vice versa, it is not completely clear. But one aspect for sure is that in bird evolution, forelimbs and thin filaments on the skin were replaced with fingerless wings and feathers that adapted to flight because it was an evolutionary advantage for such development to occur.
While liondrummer and mary both offer great explanations of how and why feathers developed into the great flight aides to birds, I think that there is another possible explanation for why feathers may have appeared in the first place. Much as the horns of rams and the antlers of deer act as a form of defense and a way to attract members of the opposite sex, feathers may have developed in the same fashion.
ReplyDelete"There is evidence that predators are particularly cautious in dealing with potential prey having bright color patterns" (Campbell, 1201). Colorful feathers may have developed as a defense mechanism from potential predators using a form of Batesian mimicry to give it a bright coloration that would fend predators off.
Feathers also could have developed as a way for the individuals to attract members of the opposite sex, so it would be able to pass on its genes to the next generation through reproduction. A modern example of birds using their feathers to attract mates would be that of the male peacock. The male peacock's tail feathers display bright and beautiful colors and designs in hopes of attracting mates for reproduction. This could also be a reason for the development of feathers, as it would be a selective advantage to have a characteristic that would make it more likely to reproduce.
Coyne states on page 53 that "evolutionary change...nearly always involves remodeling the old into the new" and on page 54 says that "natural selection can act only by changing what already exists. It can't produce new traits out of thin air." Such is the likely case with feathers. While liondrummer and mary offer great insight into why feathers are the choice tool of flight, they appear to offer little reason for why feathers developed in the first place. It is possible that they first developed as a form of defense or as a form of attracting mates, and then were chosen to be the tool of flight because they had the characteristics explained by liondrummer and mary.
Other sources:
http://www.livescience.com/animals/080821-peacock-tail.html
http://www.newton.dep.anl.gov/natbltn/700-799/nb730.htm