I apologize for the wrong answer. The corrected answer is:
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Instincts are behaviors that are innate and unlearned, and they are typically present in animals from birth. These behaviors are believed to be controlled by a combination of genetic and environmental factors. In the case of genetic factors, instincts are encoded into an animal's genetic code through the process of evolution.
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Over time, certain behaviors that provide a survival advantage for an animal become more prevalent in a population. This occurs because animals that exhibit these behaviors are more likely to survive and reproduce, passing on their genes to their offspring. As a result, the genes that are responsible for these behaviors become more common in the population.
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In some cases, specific genes have been identified that are responsible for certain instinctual behaviors. For example, in fruit flies, a gene called "period" has been found to control their circadian rhythm and mating behavior. In other cases, multiple genes may be responsible for a particular behavior, or it may be more difficult to pinpoint the specific genes involved.
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It's important to note that genetic factors alone do not determine instinctual behavior. Environmental factors can also play a role in shaping behavior, such as the conditions an animal is exposed to during development or the social environment it is raised in. Additionally, not all behavior is purely instinctual - some behaviors may be a combination of instinctual and learned components.