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 the 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. Explain how the change occurs in terms of the four postulates listed above. 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 explain the process by which the changes occurred. What is the selective pressure? Explain why the change might confer more fitness to a particular environment?
This question is quite timely given the present atmosphere of climate change. Changes to the climate will have huge effects on all of the world's species which will spur evolution in numerous populations, particularly in areas at the ends of a species range. Below I've briefly outlined one example for you. To complete this response you will need to expand on this answer in the places I've noted or chose another species and follow the outline I provide below.
The Theoretical Selective Pressure: Global warming has shifted populations of trees in the North East United States such that tree species that used to be at the Northern border ...
In this solution, a butterfly species which is experiencing habitat changes due to global climate change, is used as an example of how a particular selective pressure can cause natural selection to take place within a population. This is all completed in 415 words.