Tuesday, September 21, 2010

Introduction to the Evolution of the Human Body

This blog will be covering how the human body has evolved over time. Over the past 7 million years, the human body has evolved to adapt to climates and various geographies. The human race has its roots in Africa but as groups of people traveled and spread out further around the globe, each group developed its own unique characteristics for survival. The gradual changes led to the differences in humans around the globe today. Although we may all look, talk, and act differently, each human is still 99.9% similar in our DNA makeup. We are not only similar to each other, but we are also extremely similar to chimpanzees. In fact, “Studies indicate that humans and chimps are between 95 and 98.5 percent genetically identical,” (National Geographic).

However, the human body has evolved in several ways that make it completely different from all other species.  One of these distinctive characteristics is bipedalism, which is the ability to walk on two legs as opposed to four.  Bipedalism was the first physical characteristic that marked the difference between humans and other animals.  There are several theories about why humans switched to bipedalism, but all point to selective pressures that caused the evolutionary change.  These possible selective pressures include access to food, increase in offspring, and energy and water conservation.

The next major development that marked the difference between the human body and that of other animals was the loss of a honing canine tooth.  Apes have a honing canine to shred their food during chewing.  Humans developed nonhoning chewing because they gained the ability to make and use tools that could preprocess their food.  The nonhoning canine is smaller than the honing canine, does not project out as far, and is also not sharpened against the lower premolars.

A third, and much more recent, development that distinguishes humans from other animals is speech.  The development of the hyoid bone allowed for this characteristic.  The hyoid bone is a part of the human vocal structure.  The shape of the hyoid bone is unique to humans and reflects their ability to speak, whereas other animals can only make noises to communicate.

Although the human body has evolved over time, humans still have many functions and parts that were once important to survival, but are now essentially useless. We still get goose bumps when we are afraid or cold, but why? When early hominids had thick hair covering their bodies, goose bumps could keep them warm by trapping air between the hair and skin, which created insulation. Goose bumps also made the hair stand on end to frighten any threatening animal. In present day, however, we do not have enough hair for insulation, or to make us seem larger.

Extra ear muscles, the plantaris muscle in the foot, wisdom teeth, the third eyelid, and the tailbone are other examples of superfluous body parts left over from ancestors who lived millions of years ago. We no longer need the muscles to wiggle our ears, though some people still have them. The plantaris muscle was used for gripping and manipulating objects with our feet, something most modern-day humans no longer do. Wisdom teeth became unnecessary when our diets changed, and the third eyelid is now only common in birds, reptiles, and fish. Our tailbone (coccyx) is still believed to be used to support muscles, but is no longer an aid for swinging through trees and can be surgically removed without any effect to our health.

Related Links:

Evolution video:  http://www.youtube.com/watch?v=b1Ozky8xeFQ


Atheists, By. "Top 10 Signs Of Evolution In Modern Man - Top 10 Lists | Listverse." Top 10 Lists - Listverse. Web. 19 Sept. 2010. <http://listverse.com/2009/01/05/top-10-signs-of-evolution-in-modern-man/>.
The Human Family Tree. National Geographic, 2009.
Larsen, Clark Spencer. Our Origins: Discovering Physical Anthropology. New York: W.W. Norton &, 2008. Print.
"The Origin of Bipedalism." Web. 20 Sept. 2010. <http://www.jqjacobs.net/anthro/paleo/bipedalism.html>.
"Useless Body Parts: Human Evolution | DISCOVER Magazine." Science and Technology News, Science Articles. Discover Magazine. Web. 20 Sept. 2010. <http://discovermagazine.com/2004/jun/useless-body-parts/article_view?b_start:int=0&-C=>.

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