Opportunity costs of romantic evenings and IQ of babies

Couple of months ago we were talking with my girlfriend about the impact of season of your birth on your intelligence, and health. My theory was that less educated, poor people are more likely to conceive a child in the winter. Children born in fall and early winter underperform their peers simply because they are more likely to come from a family with low socioeconomic status.

Guess what, NBER published a paper "SEASON OF BIRTH AND LATER OUTCOMES: OLD QUESTIONS, NEW ANSWERS, 2008" that is supporting my theory. The sad thing is, that I am not the author of the paper, the cool thing is that they got it wrong (or so I believe)! They argue that less educated, poor man are more likely to be exposed to temperature extremes. Such exposure lowers their sperm count and they are less likely to conceive a child. Fine, but I think I have a more plausible explanation.

In my opinion the differences are caused by opportunity costs of making a baby. The less intelligent baby is likely to be conceived in december, january, february , and march. All of these are rather cold months.
In my opinion richer people have significantly wider choices of entertainment during the winter, but the gap narrows during the summer. In the summer you can hike, go to a park, sun bath, swim in the lake, jogg all of these without having to pay a single penny. What can you do for free in the winter? Virtually nothing! While the rich ones have wide range of possible pastimes in the winter (skiing, snowboarding, going to movies, going for a dinner and thousands more) and would have to give them in order to have a romantic evening, the poorer ones have way simpler choice: "Shall we watch TV or make love?". And this is what in my opinion drives the difference, opportunity costs of romantic evenings! On average smartest children are conceived in the months when the gap between opportunity costs of making a baby for a rich and poor are smallest. The least intelligent are conceived when the gap between the opportunity costs is the largest...