There are a number of mysteries in 1st Stage’s “The How and The Why,” an intellectually stimulating and intriguing play by Sarah Treem. Many of those mysteries can’t be talked about without giving away elements of the play’s deliciously improbable plot. But two facts that are central to “The How and The Why” can be mentioned without fear of spoiling any surprise. The first is an old notion: when it comes to discovering new scientific ideas, women can hold their own against men. The second is that, when it comes to relating to other human beings, people rely on feelings, poetry, even popcorn before they rely on scientific fact.