I don't believe in the good nature of the human being. I think we are animals, like many other animals that if not instructed will operate exclusively under the influence of our instincts. The difference, I mean the big difference is in our intelligence.
Look at the small kids and toddlers, how selfish and cruel they are (with smaller ones or weaker) and if there is no do and don't from the parent they won't realize the good from the bad (the human values ) by themselves. Conclusion: the human values and what we know as humanity is the product of the human mind and intelligence, a system of values is a must for social life, otherwise we never could come to have a collective life in a big society.