Hi doma,
That's not science. It's corruption. Fortunately, poor quality studies usually get discovered, even if there is sometimes a delay. I know it's all an illusion, but as illusions go, it's a fairly consistent body of work.
Methinks the Trobriand islanders get married pretty swiftly when they find their lover is pregnant so as not to trespass upon their taboo. Folks who don't know what causes pregnancy surely don't count the months. Probably don't have 'em in the first place. I daresay these kinds of folks operate on the same principles the rest of us do, all the same. But personally, I don't plan to test the proposition.
Seems to work much the same way for most mammals, by the way.
| 
They would also