You have learned that the organisms best suited to survive in their particular circumstances have a greater chance of passing their traits on to the next generation. But plants and animals interact in very complex ways with other organisms and their environment. These factors work together to produce the amazingly diverse range of life forms present on earth. In this activity, you will learn more about natural selection.

Natural selection happens when the environment "selects" which individuals will survive long enough to breed. You have already looked at this a little in earlier lessons. There are many examples of natural selection, but one of the most interesting is in the gypsy moth in England. The following is an excerpt on the gypsy moth and natural selection.

The best example of a quick change in the environment and a species ability to adapt concerns the color of the Gypsy Moths in England. When the industrial revolution occurred, coal and other industrial factories spewed out massive amounts of air pollutants, so much so that even during the day the skies were as dark as night. The original color of the gypsy moths was a light gray; such a color blended in with the trees in their environment and acted as camouflage against predators. With the change in the environment, the camouflage adaptation no longer functioned because the tree trunks were darker colored from the air pollution. The dark gray gypsy, once at a disadvantage and quickly eaten by predators, now survived and bred, while their lighter counterparts were eaten. As a result the gypsy moth, through adaptation and natural selection, was able to change its coloring gradually to a dark gray-black to match the surface of the trees covered in pollution. The gypsy moths did not just decide one day to change their color; at the basis of such a change was the concept of natural selection.
 

From: http://www.mnsu.edu/emuseum/biology/evolution/genetics/naturalselection.html

 

     

 

To put this in simple terms, various coloured moths were living at the same time in the same habitat; some were light-coloured and some were dark-coloured. Originally, the light-coloured moths survived better than the dark-coloured moths because their colour was similar to the trees. Predators had difficulty finding them. The dark-coloured moths were easy to see, so they were eaten. Then, the trees became dark due to air pollution from factories. The situation was reversed. Now, the light-coloured moths were easy to see and were eaten, but the darker moths survived. This event changed the habitat of the moths, and natural selection occurred to change which type of moth dominated the habitat.

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A natural disaster can cause fairly quick natural selection. For example, an unusually heavy snowfall can cause natural selection. Animals that need to get to the ground below the snow to eat may be affected because they cannot dig far enough to access food. If you have two animals that are basically the same, one might live while the other dies. The difference could be as simple as one is slightly bigger and has more fat on its body. The fat allowed it to survive, and therefore, it might reproduce and pass on its traits to the next generation.