It could evolve over time. I say that from my own experience; not sure proponents of aspects of attachment theory would agree. I am consistently evaluated to have a fully secure attachment style currently, but was most definitely not born into it. I was probably at one time somewhere more in the area of fearful-avoidant, but I was personally determined to be healthy in relationships so that I could both share and derive all the love and satisfaction deserved by myself and by my partner, and just kept re-examining my own behavior and making adjustments. While not every relationship that I was in bore improvement (I'm as apt to run in place as the next guy, at times), I did eventually learn through some trial and error what I wanted to avoid, what didn't work and what did.. so that some of the long-term relationships I was in did represent new stages in my own evolution, from fearful-avoidant to secure.

All things is possible.