Human nature is just that. Nature. One could argue that nature is predominantly evil, with hurricanes, poisonous animals, and other things like this. But you can argue the opposite as well, with mothers being naturally caring, the natural beauty of nature, and the circle of life in general. Human nature, and thus nature in general, cannot be defined as good or evil as those are both concepts created by humanity to describe things in more quantifiable terms.
Humans, by nature, are wild, random, impossible to predict. Our civilization is random, chaotic, unpredictable, and other words often given negative connotations but it's also ruled by law, love (paternal, romantic, sexual, etc...), life, and other terms given positive connotations. Humans, like most other animals are afraid of things we cannot understand. Since we cannot accurately define the force of nature, we created the concepts of good and evil. These terms gave us a sort of refuge from the fear. We could now say whether something was good or evil, but this was a problem as each person had or has their own code of morality and ethics.
I believe immediately after birth, a person is inherently good, as they come into this world in the nurturing arms of their mothers, surrounded by people who want nothing but the best for the child. But that can all change the moment the child feels pain or hunger or sadness or any other emotion.