"- oh? Why?"

"Because they're mostly religious groups that are declining in popularity and the biggest ones in my country suck in other ways." 

"So the variance appears to be mostly memetically driven?"

"Oh! Yeah." 

"That's amazing! What's wrong with them apart from the irresponsible - and not so irresponsible, in their environment - encouragement of having children?"

"They're conservative nutjobs who hold onto theologically obsolete scientifically nonsensical worldviews of varying unpleasantness and obviousness of how dumb they are." 

"- theologically obsolete?"

"They're one faction of a religion and most of the other factions have moved on already." 

"Huh. All right then. No obvious sign of biologically driven uptick in desire for children?"

"Not yet. I did say--oh. Right. So, when I said 'decades,' I forgot to mention that one of our years is only the length of one of your seasons."

"...Ah. Yes, that would make it pretty hard to notice an effect that was anything less than staggering."

"Yep! It might become a problem in the future, but we don't have the springing thing so we've got a lot more habitable area to spread out into, so I'm not worried." 

"Population grows exponentially, though."

Shrug. "We'll figure something out. Less of a time crunch, is all. And at some point I bet we're gonna terraform Mars, it'll be great." 

"Mars is suitable enough to work well for the purpose?"

"Yeah, probably, it doesn't have much magnetic field but it has its own water--frozen right now, but--and may have had life at some point! Not complex life but oh well. I don't think we're likely to terraform Venus anytime soon, hoo boy, that atmosphere." 

"And it doesn't matter how long its seasons are, to you, I suppose."

"Yeah, we're fertile year-round. And less crazy in the head about it than Amentans are during spring." 

"Is there much variance there? Any obvious trend?"

"In, what, libido? Hopelessly confounded by cultural factors." 

"If that was running all your reproductive drive for so much of your evolutionary history... where do the cultural factors come in exactly...?"

"Humans like sex a lot. Who likes it how much compared to who else is the kind of thing it's next to impossible to collect data on because different cultures have way different taboos on the subject." 

"Huh! Taboos like what?"

"Well, like, most of our cultures have historically had strong monogamy norms, or strict polygyny or occasionally polyandry--the fertile year-round thing caused some weird gender differentiation in terms of sexual norms--in some cultures this is taken so strongly that a woman being alone with an unrelated man she isn't married to is seen as dishonorable, and if you showed up at her door asking questions about her sex drive her brothers would probably shiv you. And then in more progressive countries a lot of the old taboos and norms are breaking down in some subcultures, and you have a lot of exploration-of-sexuality happening there, and some people in them would probably overreport their sex drive and kinkiness to a surveyor." 

"Huh," he says. "- may I sit down?"