true or false?

The necessity of origin thesis says that a necessary condition for being who you are is that you came from the particular parents that you actually came from.  Thus construed, the necessity of origin thesis entails the truth of the following subjunctive conditional:

Had your parents not, you know, got it on, then you would not have existed.

Apparently, the Nobel Laureate poet Wislawa Szymborska disagrees:

I am who I am.
A coincidence no less unthinkable
than any other. 
I could have different
Ancestors, after all. 
I could have fluttered from a different nest 
Or crawled bescaled from under another tree.