Talking over a beer

Two guys were sitting around talking one afternoon over a cold beer.
After a while the first guy says to the second,
"If I was to sneak over to your house and make love to your wife while you was off fishing’, and she got pregnant and had a baby, would that make us related?”
The second guy crooked his head sideways for a minute, scratched his head, and squinted his eyes, thinking really hard about the question.
Finally, he says,
"Well, I don't know about related, but I reckon it’d make us even."