What are the factors that influence the process of evolution?

Evolution occurs when certain random mutations are selectively favoured for as they allow for a survival advantage over other individuals of the same species. For example, a random mutation in one giraffe will have allowed it to grow a longer neck. This giraffe would therefore be better at reaching food compared to other giraffes. This increase in food availablity means the giraffe is more likely to survive and pass on the 'long neck' gene as it is less likely to starve. Gradually, as generations pass and the long neck giraffes are more likely to live to pass on their gene, this presence of the long neck gene increases throughout the giraffe population. Factors such as food availability, predators, climate changes, competition for mate all influence which genes survive in a population. Hope this helps!