in which the change, can be environmentally caused
the idea of random is believed, as the 'cause' is unknown......
Not exactly Bishadi,
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.
There are different ways in which evolution occurs, the most noted are natural selection and adaptation, change also occurs through sexual selection.