Economic Population Control

Senator Fowler nodded. "One other little point, Charlie. Just how often do your reproductive castes breed, anyway?"

It was Jock who answered. When Charlie hesitated, David Hardy watched with interest-was there communication by gesture? "When they are allowed to," the alien said smoothly. "Don't yours?"

"Eh?"

"You control your populations through economic incentives and forced emigration. Neither alternative is available to us, yet our reproductive drives are no less strong than yours. Our Masters breed when they can."

"You mean you have legal mechanisms to restrict population?" Horvath asked.

"Essentially yes."

[...]

The Moties twittered for a moment. "Abstinence is common," Jock said. "We also have chemical and hormonal methods like yours. Do you wish the mechanics discussed here?"

"I'm more interested in the incentives," Senator Fowler said heavily. "What happens to Masters, or Browns, or whatever, if they start having children every six months?"

"Would you not define that as an action placing independence as more important than the interests of the race?" Jock asked.

"Yeah."

"So do we."

"And that's how you get wars started," Dr. Horvath concluded. "Senator, with all respect I think we've got the answers to our questions. The Moties control their populations. When individuals fail to go along, there's conflict. Sometimes that leads to wars. Just how is this different from humans?"

The aliens use war as a form of population control, while humans use economics.