Our nature is our genetic endowment. It determines our basic physical layout, hair and eye color, and form. But more importantly, it determines the types of emotions and motivations we can experience (e.g. happiness, sadness, fear, etc.) which are finite in number. We can never experience any entirely new emotion without an evolutionary change to our genetic material.
Our nurture, then, is the experience we have during our lifetime. But it is not just any experience. It is experience that resonates with our motivations and emotions; in other words, our inner eye. Any other experience we have, we essentially ignore.
Our inner eye draws us toward certain experiences, and ignores others. Society may tell us to act in certain ways, but if our inner eye does not motivate us to do what society tells us, we will not do it. Most people are motivated or guilt-ridden by the dictates of culture, but some are not. How would we know to detect something called "society" and place importance on its messages (as opposed to, say, hyena howls) unless this detection and reaction were innate?
Indeed, should society's messages be considered nature or nurture? On the face of it, they seem to be purely experiential. But this may be too simplistic. What is society, if not a collection of genetic beings? Society formed because people have a genetic impulse to group together. The tendency to feel loneliness and isolation when away from society is genetic, as all emotions are. Culture is an expression of our common tendencies as individuals. So society, at some level, is a complex genetic creature, and the messages it gives back to individuals must be in part genetic as well.
Many people offer rationalizations and justifications for why people are the way they are because of how they were nurtured. This is the tiring fodder of cheap biographies. For example, "Joe is so aggressive because he was the youngest child and had to compete with his older siblings." Does that mean that every youngest child is aggressive? "Bill is constantly seeking to please because his father was an alcoholic." Does that mean every child of an alcoholic seeks to please? No, of course not. These are just after-the-fact justifications. Our inner eye responds in different ways to different environments, but no two people respond the same way in the same situation, due to the distribution of traits across society.
We only retain or seek out experiences (nurture) which resonate with our genes (nature). Parents can try to force their daughters to play with fire trucks and baseball bats, but girls will usually reject them, and return to playing with the dolls they love. Most people deny this simple fact, until they have children and then sheepishly admit it.
The larger question still remains as to what invariants, fuzzy and inexact as they are, the inner eye can recognize in the environment, and what "trigger points" or "branching points" are set up in the inner eye to respond. The inner eye has little power except the recognition of vague landmarks in the environment (as a frog can recognize blurry dots in the sky and associate them with flies for its dinner).