3modEoEv

One common misconception about evolution is that, “It’s just a theory. Scientists have never been able to observe it happening.” This statement could not be more wrong. In class today, we learned about three modern examples of evolution that have occurred within the course of human history.

The first example was the peppered moth. During the industrial revolution, pollution changed the landscapes in urban England. The white trees that the moths lived on were suddenly covered in black soot. In response, the peppered moths began exhibiting a recessive trait; instead of being white with black flecks, the moths changed to be fully black. This was one of the first examples of evolution observed after Darwin’s theory was published. Ironically, when England began to curb its pollution problems, the moths evolved into their original color!

The second example was one that involved humans themselves: the evolution of human skin. Since the human species left Africa about 200,000 years ago, our skin tone has been evolving. One of the important trade-offs regarding skin tone deals with sunburn protection vs. our ability to capture vitamin-D. A human with dark skin will have a harder time capturing vitamin-D, but will be less likely to become sunburned. And someone with lighter skin will have the opposite problem. As a result, those humans in northern climates (Ireland, Norway, etc.) evolved to have pale skin, while those in sunnier climates (Africa, Spain, India, etc.) evolved to have darker skin.

The last example was certainly the scariest: drug-resistant bacteria. When Alexander Fleming discovered penicillin in 1923, he changed the world. Suddenly, diseases like tuberculosis and pneumonia were entirely curable. And as a result, human life expectancy rose. But there was another result too. Because penicillin is most effective at killing the weakest bacteria, the stronger bacteria were often the lone survivors left to reproduce. Over the past hundred years, the germs have been evolving, getting stronger and stronger each time they are exposed to penicillin or other antibiotics. “It used to be that physicians could select almost any antibiotic to treat a patient,” says Richard Glew, M.D. “But that Golden Age of antibiotic use is over. The germs are winning.”

April 4 – Modern Examples of Evolution (pg 611)

Your HW tonight is to play the Peppered Moth Game (click here to access).
Be sure to read the three pages of instructions and to finish by playing the
computer game at the end (called “A Bird’s Eye View of Natural Selection”)

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