Details: According to the Theory of Evolution, Natural Selection is the mechanism by which evolution occurs.
The process of Natural selection is based on the following four postulates (listed in your textbook on page 288):

Postulate 1 - Individual members of a population differ from one another in many respects.

Postulate 2 - At least some of the differences among members of a population are due to characteristics that may be passed from parent to offspring. That is, they are heritable or genetic.

Postulate 3 - In each generation, some individuals in a population survive and reproduce successfully but others do not.

Postulate 4 - The fate of individuals is not determined by luck. Instead, an individual's likelihood of survival and reproduction depends on its characteristics. Individuals with advantageous traits survive longest and leave the most offspring, a process known as Natural Selection.

Choose an animal species. Your goal is to describe the way in which an evolutionary change might occur for a particular characteristic (trait) of that species as a result of natural selection. The characteristic could be something like coloration pattern, length of the limbs, or size of the teeth or beak, or any measurable trait that is inherited.

The organism you choose should be a real one but the evolutionary change you describe can be real or theoretical.

Remember: evolution occurs at the level of the population. Individuals do not evolve, populations evolve.

describe how the change occurs in terms of the four postulates listed in the book.

You will describe what the population starts out like at time zero and then what it will look like at a later time, as a result of natural selection. Make sure to describe the process by which the changes occurred.

What is the selective pressure? describe why the change might confer more fitness to a particular environment?