Paul Bloom studies the moral lives of infants:
[O]ur initial moral sense appears to be biased toward our own kind. There’s plenty of research showing that babies have within-group preferences: 3-month-olds prefer the faces of the race that is most familiar to them to those of other races; 11-month-olds prefer individuals who share their own taste in food and expect these individuals to be nicer than those with different tastes; 12-month-olds prefer to learn from someone who speaks their own language over someone who speaks a foreign language. And studies with young children have found that once they are segregated into different groups even under the most arbitrary of schemes, like wearing different colored T-shirts they eagerly favor their own groups in their attitudes and their actions...
The aspect of morality that we truly marvel at its generality and universality is the product of culture, not of biology. There is no need to posit divine intervention. A fully developed morality is the product of cultural development, of the accumulation of rational insight and hard-earned innovations. The morality we start off with is primitive, not merely in the obvious sense that it’s incomplete, but in the deeper sense that when individuals and societies aspire toward an enlightened morality one in which all beings capable of reason and suffering are on an equal footing, where all people are equal they are fighting with what children have from the get-go.