It sounds like the original colony was flirting with being below the minimum viable population sufficient to prevent extinction, especially on a new world where the colonists would inevitably face unforeseen challenges. As a biological matter, they should have placed a high value on maximizing the genetic diversity of their limited population, yet they did the opposite. Earth almost certainly saved them from extinction.

I'm reminded of an early episode in the amazing reboot of Battlestar Gallactica (the Edward Olmos version was so much better than Lorne Greene's cheesy Star Wars knock-off) where the woman who survives the destruction of the colonies to become the presdient of the fleeing remnant of humanity looks at the low and declining number of people in the fleet and says, "We're going to have to start having babies," and a startled Colonel Tigh (played by Michael Hogan) looks at her and says, "Is that an order?"