I do not think that people are "naturally" either polyamorous or monogamous. It's dependent on your personal circumstances, your experiences throughout your life, and the things you learned, your attachment style (which develops from how you're raised by your parents as a child) etc. Someone with secure attachment may be more likely to be comfortable in polyamory than someone with anxious attachment for example.

I also don't believe that people "choose" whether they feel attraction to other people or not. Monogamous people feel attraction to others all the time, they just choose not to act on it.

I think the more important reason to care about regarding polyamory is whether you seek other partners out of a sense of lack, vs a sense of abundance. If you feel your existing partner has something lacking, and you seek it elsewhere, that's likely to not work out well for the health of your existing relationship. If you feel content in your existing partnership for what it is, and then you wish to share your love with people that you organically develop feelings for (rather than seek out simply because one person is not enough for you, and so you need someone to be a "third" rather than just for themselves), it's more likely to be healthy.