In the book of Romans the Apostle Paul writes, “when Gentiles, who do not have the law, do by nature things required by the law, they are a law for themselves, even though they do not have the law, since they show that the requirements of the law are written on their hearts, their consciences also bearing witness, and their thoughts now accusing, now even defending them” (Rom. 2:14-15, NIV, emphasis mine).
This is one of the key biblical passages supporting the idea that human beings have an innate moral sense, that is, an inborn sense of the difference between right and wrong. This is, of course, a controversial idea, but recent studies might actually provide empirical evidence for the doctrine. See this report regarding some fascinating research conducted by Yale University Psychologist Paul Bloom, and draw your own conclusions.