Friday, March 25, 2011
Owen's Digits
On page 36, Neil Shubin mentions Owen's pattern which instigates the composition of the fin slowly separating into the bones that make up a human hand throughout evolutionary history. However, the fin that Shubin discovered had 8 finger-like bone structures instead of five. Explain why evolutionary history benefited 5 fingers over any other number of fingers. Discuss polydactyly.
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Humans have very distinct actions that they can perform that no other creature can do because of human's unique hands. The main part of the hand that gives it its unique abilities is the thumb as it allows a strong grasp. Four fingers as well allows for the strong grasp and dealing with tedious activities. By having less fingers, they can be both stronger and can be controlled independently and more precisely. Evolution moved towards this hand structure because now humans did not necessarily need physical strength to survive as they could use their hands to outsmart the other creatures. By, "it giv[ing] us both a precision tool and a power grip" (http://www.wsu.edu/gened/learn-modules/top_longfor/phychar/09_hands.html), it allowed for more of the five fingered hand organisms to survive and reproduce causing evolution to occur.
ReplyDeletePolydactyly is when another digit is on a hand or foot and usually is not a fully functional finger. One can notice that there is neither an advantage or disadvantage to having this extra finger in the way that the condition still exists and is autosomal recessive. Obviously this condition cannot be a large disadvantage considering that it has not been fully removed from the human gene pool. One can alos come to the conclusion that polydactyly is not an advantage because it has not become more prominant therefore proving there is no evolutionary advantage. On the other hand, one could also look at the viewpoint that humans are not changing anymore due to new technologies that allow basically anyone to live.
Jackie James
(jackie.james@comcast.net)
As Jackie described, Polydactyly is a condition in which an organism has additional fingers or toes. She also described that it is autosomal recessive and therefore not very common. However, this condition can also occur without a trait for it being passed down from generation to generation of a family. Furthermore, it is a condition most prominent in African-Americans than any other ethnicity (1). I think this can be due to African-Americans past as slaves. In this way, I think it contradicts what Jackie said that the condition doesn’t serve as an advantage. Fingers serve five functions. They flex, extend, abduct, adduct, and circumduct. Flexing and extending fingers relate to strength of the finger muscles while abducting, adducting, and circumducting relate to the positioning of a finger. Like any other muscle, the stronger the muscle, the more it can function. This is where it becomes a unique trait to African Americans.
ReplyDeleteIt is well known that before there were African Americans, there were African slaves in America. White colonists of the New World capture Africans and forced them to work on their plantations harvesting crops. The slaves spent endless days working under the hot sun planting, plowing, and working in the fields. Countless generations of African Americans have a beginning in slave labor. The type of work they did put stress on their hands and fingers and toes that no other ethnicity had ever experienced before. This type of work would have been made easier with an increased number of fingers that were able to handle the stress accompanied with the type of work being done. Therefore, it would become an advantage for slaves to have more fingers.
According to Darwin’s theory of natural selection, a member of a species that acquires a selective advantage will be able to attain necessary resources better. Since there is known competition for resources, especially amongst slaves, those that have a better means of attaining the resources will also be able to more successfully reproduce. This reproduction will lead to the trait that allowed the ability to better obtain the resource to be passed down again and again (Campbell 15). Therefore, if a slave were to suffer from Polydactyly, it might actually benefit the slave. If it actually benefitted the slave to have more fingers, than natural selection would insure that Polydactyly would be passed down. However, if this hypothesis is true, it would seemingly not account for the trait being so rare. Evolution though, is not a short process. For the change to have fully taken place, it would have to have occurred over hundreds and hundreds of years. The fact that the trait is still reoccurring in African Americans actually serves as evidence to the extreme benefits of Polydactyly.
1.http://www.nlm.nih.gov/medlineplus/ency/article/003176.htm
-Robbie Thomashow
(diehardcubsfan93@comcast.net)