Puppeteer-manipulated experiment in human genetc engineering that set up lotteries for the right to breed. The random drawing guaranteed a flatlander the right to be a parent regardless of the state of his or her genes or social conduct. Only the luckiest flatlanders could breed, selecting successive generations of luckier humans.
On Earth after the reform of the Fertility Laws following a scandal in 2650, each year the number of births assigned by the Fertility Board fell short of the deaths. To keep the population stable, the shortfall was made up by a lottery, with drawings each New Year's Day. Ten to 13 percent of each generation was a result of the lottery. Louis Wu had one child by lottery, and Teela Brown was the descendant of five generations of Birthright Lottery winners. [Spoiler alert: Ringworld] During the First Ringworld Expedition in 2851, Nessus revealed that Puppeteers had manipulated members of the Fertility Board, with bribery and blackmail, to create the scandal, and then to create the Birthright Lottery. He claimed Puppeteers wanted to make Humans luckier.
The Fertility Board was involved to that end.