In 1920, John B Watson of Johns Hopkins University, showed that we are born with the ability to feel fear. These days his experiments with infants would be considered unethical and could not be conducted. Anyway, he found that although a baby will show fear of a loud noise, it will not show fear of a close naked flame until it is brought close enough to be uncomfortably hot. A baby is able to feel the 'fear emotion' but fear will only be manifested once the danger source is physically experienced. Anticipation of danger will only manifest fear once the danger has been associated with an unpleasant physical outcome. I suspect that a similar pattern applies to all the emotions. The capacity to have them is innate; the manifestation is associated with experience. Initially pleasant/unpleasant physical experience and, later, anticipated physical experience. The role of emotion is to guide behaviour. It also signals our feelings to others. It evolved simply because it was 'adaptive' ie, it was conducive to survival and eventual procreation.
I believe that a pattern similar to the one I describe above applies to adaptive behavioural characteristics such as; language, ethics, intelligence, religious belief, morality and conscientiousness. I have suggested that the human genome has been 'primed' into gene-variants that support/ encourage these adaptive behaviours but that their precise nature and particular manifestation is dependent on the 'triggers' that are experienced by developing children. They are born with the pre-dispositions but life-experience determines the detail.
This is my 'Genetic Priming' theory in a nut-shell. In a more technical paper available on the Internet at http://tinyurl.com/l6bure I explain how this priming has occurred over evolutionary time.