commute
Explanation
The Joke
A man says to a woman, "Help me put this condom on and then we'll make love." The woman, wearing large glasses, asks: "Is that procedure commutative?" The man responds with a confused "What?" The caption below reads: "This is how mathematicians are conceived."
The woman is asking whether the order of operations matters -- in mathematics, a commutative operation is one where changing the order of the operands does not change the result (e.g., 3 + 5 = 5 + 3). She is asking whether they could reverse the order: first make love, then put on the condom. Obviously, in this context, the order very much matters.
The Humor
The humor operates on a brilliant double level. First, there is the absurdity of applying mathematical terminology to an intimate situation where the answer is obviously "no, order matters here" -- making love before putting on a condom defeats the entire purpose. Second, the caption delivers the meta-punchline: the joke implies that people who think this way (applying math to everything, including bedroom activities) are the ones who produce mathematician children. There is an additional layer suggesting that if the procedure were actually performed in the reversed (commutative) order, the resulting unprotected encounter would indeed be how mathematicians (or any children) are literally conceived.
References
In mathematics, commutativity is the property that the order in which two elements are combined does not affect the result. Addition and multiplication of real numbers are commutative (a + b = b + a), while subtraction and division are not.