“This gives weight to the fact that helping my relatives helps preserve my genes.”
Helping your relatives may or may not help preserve your genes. If you read this whole New Yorker piece, you see that the writer isn’t expressing this concept as fact. It’s a theory, perhaps, but not something we know for sure.
We often use fact when what we really mean is notion or idea. (And that’s a fact.)
As to the theory itself, my interest in preserving my genes is tempered by the question of exactly how much money my relative is asking for.
English Is A Complicated Language 