We exist before we are birthed... whether you believe the soul enters the body at birth or conception it doesn't much matter because the soul still pre-exists the form.
Its my current opinion that the soul choses a genetic or cultural framework to experience a lifetime in (nature). They may even gravitate to certain families or groups (creating pockets of collective consciousness and bondings)However... from birth onward I feel that the core personality is subject to its environment and choices are considerably reduced. For instance ... lets speculate that the soul carries defining experiences and memories, this entity is now relearning to communicate and interact with this new life ... happiness and hurts form us as we study and assimilate our environment (which is formed by our nuturer's choices and intentions)....the first 9-12 years, maybe?
The road from childhood to adult is an intense one frought with events capable of altering our personality and physiology in a variety of ways. Who we are is chiseled and shaped by our environment, its who we are when we enter adulthood and have grown into our independance and maturing strengths.
Again... all these accumalitive experiences shape human nature as maturity, security and power sails us through lifes waters, we exist in the security of our own existance and our lives. As we age we can look upon the lessons learned or the pains born and perhaps take something from life ...Each stage of our life shapes our nature, and our soul's evolution
When we become elders, its a time of harvest and preparation, we have lived and learned, our goal being to pass on our experiences ... a time of memory and knowledge. All that life, time and experience has nurtured us with has become our nature, the one we will pass from this existance with... perhaps it will be powerful enough to carry onward into future incarnations.
So although our nature is the lens we interact through, our environment that has a equally defining impact on us.