What is natural selection?
natural selection is basically certain traits that have changed in animals as they have evolved. These traits have helped animals survive. Only the animals with the best traits survived and produced so that these animals would survive for much longer.
here is basically how natural selection works
1. There is variation in traits.
For example, some beetles are green and some are brown
2. There is differential reproduction.
Since the environment can't support unlimited population growth, not all individuals
get to reproduce to their full potential. In this example, green beetles tend to get eaten by birds and survive to reproduce less often than brown beetles do.
3. There is heredity.
The surviving brown beetles have brown baby beetles because this trait has a genetic basis.
4. The more advantageous trait, brown coloration, which allows the beetle to have
more offspring, becomes more common in the population. If this process continues, eventually, all individuals in the population will be brown.
The environment of earth is in a constant state of flux, but changes in an environment generally occur within time spans of tens of thousands of years, save for a few examples where changes occurred in an interval of a 100 or 200 year time span.
The best example of a quick change in the environment and a species ability to adapt concerns the 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 gradually change it's coloring to a dark gray-black, to match the surface of the trees covered in pollution. The gypsy moths didn't just decide one day to change their color, at the basis of such a change was the concept of natural selection
sources:
http://www.mnsu.edu/emuseum/biology/evolution/genetics/naturalselection.html
http://evolution.berkeley.edu/evolibrary/article/evo_25
http://anthro.palomar.edu/evolve/evolve_2.htm
http://en.wikipedia.org/wiki/Natural_selection
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