In my own case, I certainly chose to enter into a plural relationships, however I think that everyone has the inate capacity to love more than one person. Wither we do so one person at a time, or multiple partners at the same time depends on a variety of conditions, beliefs, life experiences, and or societal/religious expectations.
I think it's important to clearly define what you mean by "being polyamorous." Do you mean "having polyamorous relationships" or do you mean "having the capacity to love multiple people simultaneously?" One is a choice, the other is innate.