The Mariposans were a group of Humans who inhabited the Mariposa colony in the Ficus sector. They founded their colony in the mid-22nd century, on the planet where their ship, the SS Mariposa, crash landed.
Only five colonists (two females, three males) survived the crash landing, including the Mariposa commander, Walter Granger, so they became the first Mariposans. Unfortunately, they knew that two women and three men comprised a gene pool too shallow to sustain a stable population, they looked to cloning as a way to survive. Future generations later referred to the original five as the "progenitors".
As a result of the cloning process, the Mariposans suppressed their natural sex drives through a combination of drugs and punitive laws, to the point that they found sexual reproduction undesirable. Furthermore, over time, they suffered from replicative fading and were facing extinction during the 24th century, unless new genetic material could be obtained.
The existence of the Mariposans was revealed to the Federation in 2365 by the nearby Bringloidi, who were also descended from Mariposa colonists and had recently been evacuated by the USS Enterprise-D. The Mariposans asked the Enterprise crew for DNA which they could use to continue their colony. When they refused, the Mariposans attempted to steal it from William T. Riker and Katherine Pulaski through their epithelial cells, erasing their memories afterwards. However, they eventually found out and considered this a breach of their personal rights, terminating the clones before they reached maturity.
As a solution, Captain Jean-Luc Picard proposed merging the Mariposan population with the Bringloidi. Thirty couples were available between the two groups, which was technically enough to create a viable genetic base; however, Dr. Pulaski recommended to broaden the base for a safer and healthier society. This meant that each woman, from both groups, had to have at least three children by three different men. This, however, also meant that monogamous marriages would not be possible for several generations. (TNG: "Up The Long Ladder")