Good Golly Miss Molly
So I found this astonishing (to me) information today:
Almost all female Mollies are pregnant. [...] most female Mollies will release babies about once a month. Female Mollies can deliver several batches of babies without a male in the aquarium. So once your female Molly is pregnant, you don't really need a male Molly for several months.
I see. I still blame TV's Fish Girl for telling me her life story instead of this, but I guess she might at least indeed have given me only Miss Mollies.