Some food preferences may be acquired through learning, rather than being innate. Humans often learn what is good or not good to eat from those around them (e.g. parents and peers). Parents have a large influence on food preferences, as they buy and serve the food that young children eat. They also positively reinforce children for eating certain foods (operant conditioning). Children may also learn their food preferences through social learning. They may observe and imitate their peers, or their preferences may be shaped by media advertising.