Two things that INCREASE population, would be an increase in leisure space. Another is if the area is sustainable for life. Two things that would DECREASE population, would be a scarcity of any required resources. A decrease in space, and not a sustainable area.
More recently, stem cells from the blood stream (called peripheral blood stem cells) and umbilical cord stem cells have been used to treat some of the same blood-based diseases.
If I had to guess it would be C metabolism
The purines-adenine and guanine