[BlackAtrocity]

It all really depends on the size of the animals brain. Animals tend to have smaller brains than humans which means they have less decision making powers. If you took a fish for example, it would act the same way every time almost to whatever stimuli you give it. That's just the way it works. Most mammals however have larger brains than most of the other animals. They therefore tend to have more responses to stimuli. That is probably why most of the instinct you see tends to be in your lower animals because their brains are less developed so they tend to do the same thing every time, hence instinct. This is a topic where my 10th grade biology finally came in handy.